[PATCH v7 00/13] leds: Add support for hardware-initiated hardware control trigger transition

[PATCH v7 00/13] leds: Add support for hardware-initiated hardware control trigger transition

[Rong Zhang]

Some laptops can tune their keyboard backlight according to ambient
light sensors (auto mode). This capability is essentially a hardware
control trigger. Meanwhile, such laptops also offer a shrotcut for
cycling through brightness levels and auto mode. For example, on
ThinkBook, pressing Fn+Space ("shortcut") cycles keyboard backlight
levels in the following sequence:

  1 => 2 => 0 => auto => 1 ...

Recent ThinkPad models should have similar sequence too.

However, there are some issues preventing us from using a private
hardware control trigger:

1. We want a mechanism to tell userspace which trigger is the hardware
   control one, so that userspace can determine if auto mode is on/off,
   as well as turing it on/off programmatically without obtaining the
   trigger's name via other channels
2. Writing brightness has the side effect of disabling hardware control,
   but the hardware control trigger remains active, resulting in the
   software and hardware being out of sync. Most LED drivers that
   supports hardware control also suffer from the same issue
3. Turing on/off auto mode via the shortcut cannot activate/deactivate
   the corresponding hardware control trigger, making the software state
   out of sync
4. Even with #3 solved, deactivating the hardware control trigger has
   the side effect of emitting LED_OFF, breaking the shortcut cycle,
   especially "auto => 1"

This series tries to demonstrate a path on solving these issues:

- Introduce an attribute "trigger_may_offload_to_hw", so that userspace
  can determine:
  - if the LED device supports hardware control (supported => visible)
  - which trigger is the hardware control trigger selected by the LED
    device and offloaded to hardware ("[foo_trigger]")
    - A callback hw_offloaded() is added so that LED triggers can report
      their hardware control state
- Remove hardware control trigger when writing brightness
- Add led_trigger_notify_hw_control_changed() interface, so that LED
  drivers can notify the LED core about hardware-initiated hardware
  control transitions. The LED core will then determine if the
  transition is allowed and switching between "none" (i.e., no trigger)
  and the device's private trigger accordingly
  - This capability is restricted to the device's private trigger. If
    the current trigger is neither the private trigger nor "none", no
    transition will be made
  - This interface is gated behind Kconfig LEDS_TRIGGERS_HW_CHANGED and
    LED device flag LED_TRIG_HW_CHANGED
- Tune the logic of trigger deactivation so that it won't emit LED_OFF
  when the deactivation is triggered by hardware

The last three patches are included in the series to demonstrate how
these interfaces are supposed to be utilized, so that ideapad-laptop
can expose the auto mode of ThinkBook's keyboard backlight. They can be
submitted separately once the dust settles, if preferred.

[ Summary of other approaches ]

< custom attribute >

Pros:
- simplicity, KISS
- no need to touch the LED core
- extensible as long as it has a sensor-neutral name
  - a sensor-related name could potentially lead to a mess if a future
    device implements auto mode based on multiple different sensors

Cons:
- must have zero influence on brightness_set[_blocking] callbacks
  in order not to break triggers
  - potential interference with triggers and the brightness attribute,
    can't solve #2
- weird semantic (an attribute other than "brightness" and "trigger"
  changes the brightness)

< private hardware control trigger (this series) >

Pros:
- mutually exclusive with other triggers and the brightness attribute
  (hence less chaos)
- semantic correctness
- acts as an aggregate switch to turn on/off auto mode even a future
  device implements auto mode based on multiple different sensors
  - extensibility (through trigger attributes)

Cons:
- complexity

[ Previous discussion threads ]

https://lore.kernel.org/r/08580ec5-1d7b-4612-8a3f-75bc2f40aad2@app.fastmail.com
https://lore.kernel.org/r/1dbfcf656cdb4af0299f90d7426d2ec7e2b8ac9e.camel@rong.moe

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Add a new patch to the series to collect existing trigger attribute
  stuff together into led-triggers.c (thanks Lee Jones)
- Leave all new attribute stuff at led-triggers.c (ditto)
- Rename the offloaded() callback to hw_offloaded() (ditto)
- Rename the trigger_may_offload attribute to
  trigger_may_offload_to_hw (ditto)
- Use "[foo_trigger]" to represent a selected and offloaded trigger, and
  no longer use a dedicated container to represent selected but not
  offloaded ones (ditto)
- Remove messages mainly for debugging (ditto)
- Inline led_trigger_{init,destroy}_hw_changed() into led-class.c by
  exporting led_trigger_hw_control_changed_worker() (ditto)
- Rephrase some comments and messages (ditto)
- Constify device attribute trigger_may_offload_to_hw
- Address a concern from Sashiko
  - Fix printf format string
  - https://sashiko.dev/#/patchset/20260902-leds-trigger-hw-changed-v6-0-55693cd78877@rong.moe?part=11
- Link to v6: https://patch.msgid.link/20260902-leds-trigger-hw-changed-v6-0-55693cd78877@rong.moe

Changes in v6:
- New patch in the series to address a concern from Sashiko
  - [PATCH 1] leds: class: Always protect brightness_show() with led_access
  - https://sashiko.dev/#/patchset/20260821-leds-trigger-hw-changed-v5-0-3e00d6c4a936@rong.moe?part=7
- Update Date: and KernelVersion: for the document of
  /sys/class/leds/<led>/trigger_may_offload
- Implement workqueue deferal mechanism
  - Protects ideapad_kbd_bl_led_cdev_brightness_set() with the new mutex
    as well
  - No longer convert last_hw_brightness into atomic_t as it's not
    required now
  - https://msgid.link/e2b081dfd8f96511a73b86ab3ec75e5cd759b79b.camel@rong.moe
- Simplify the auto mode state preservation logic by converting
  `priv->kbd_bl.initialized' into a tristate integer
- Link to v5: https://patch.msgid.link/20260821-leds-trigger-hw-changed-v5-0-3e00d6c4a936@rong.moe

Changes in v5:
- Address a concern from Sashiko:
  - Non-atomic update of led_cdev->flags causes a data race that can
    drop the LED_UNREGISTERING flag
  - Fix it by synchronize the update with trigger_lock
  - https://sashiko.dev/#/patchset/20260802-leds-trigger-hw-changed-v4-0-f97e2ca976fe@rong.moe?part=8
- Address a concern from Sashiko:
  - led_trigger_notify_hw_control_changed() might sleep, but without any
    internal deferral mechanism or annotation
  - Annotate the method with might_sleep(), since the very first users
    of the interface, i.e., ideapad-laptop and (supposedly)
    thinkpad_acpi, will call the interface from work contexts. It does
    not deserve the overhead of internal deferral mechanism
  - https://sashiko.dev/#/patchset/20260802-leds-trigger-hw-changed-v4-0-f97e2ca976fe@rong.moe?part=9
- Update "Changes in v4" to include more details
- Link to v4: https://patch.msgid.link/20260802-leds-trigger-hw-changed-v4-0-f97e2ca976fe@rong.moe

Changes in v4:
- Drop the RFC prefix
- Add a new patch in the series to address a concern from Sashiko
  - [PATCH v4 08/12] leds: trigger: Do not attach trigger to a removing LED
  - Without it, the following patch may expose a race condition if a
    future LED driver synchronizes led_classdev_unregister() and
    led_trigger_notify_hw_control_changed() poorly. The ideapad-laptop
    patches in the series doesn't expose the race condition though
  - In theory, the race condition can also be triggered by a userspace
    program writing to the "trigger" attribute right before
    device_unregister() is called
  - https://sashiko.dev/#/patchset/20260719-leds-trigger-hw-changed-v3-0-5fb55722e36e@rong.moe
- Address other concerns from Sashiko
  - Reject insane hardware brightness
  - Do not notify the LED trigger core when the registration of the
    private trigger has failed
- Enable LEDS_TRIGGERS_HW_CHANGED by default when
  LEDS_BRIGHTNESS_HW_CHANGED is enabled
- Add missing #include (Thanks Ilpo Järvinen)
- Remove needless #include (ditto)
- Remove needless code alignment (ditto)
- Link to v3: https://patch.msgid.link/20260719-leds-trigger-hw-changed-v3-0-5fb55722e36e@rong.moe

Changes in v3:
- Integrate https://lore.kernel.org/all/20260712-leds-hw-control-brightness-set-v1-1-1de593b09d26@rong.moe/
  into the series
  - Adopt __led_trigger_is_hw_controlled() in the rest of the series
- Rearrange the series so that the code using the offloaded() callback is
  introduced before the driver implementation (thanks Thomas Weißschuh)
- Reword documentations and commit messages (ditto)
- Adopt guard() and lockdep (ditto)
- Address concerns from Sashiko
  - Fix a race condition in ideapad_kbd_bl_led_cdev_brightness_set()
  - Fix trigger re-registration of ideapad_kbd_bl_auto_trigger
  - https://sashiko.dev/#/patchset/20260618-leds-trigger-hw-changed-v2-0-c28c44053cf3%40rong.moe
- Make registration failures of ideapad_kbd_bl_auto_trigger non-fatal
- Link to v2: https://patch.msgid.link/20260618-leds-trigger-hw-changed-v2-0-c28c44053cf3@rong.moe

Changes in v2:
- Restrict the led_trigger_notify_hw_control_changed() interface to
  private triggers only
  - Drop PATCH v1 1/9 ("leds: Load trigger modules on-demand if used as
    hw control trigger"), not relavant any more
- Gate the led_trigger_notify_hw_control_changed() interface behind
  Kconfig LEDS_TRIGGERS_HW_CHANGED and LED device flag
  LED_TRIG_HW_CHANGED
- Fix lock ordering inversion
- ideapad-laptop:
  - Only call led_trigger_notify_hw_control_changed() when needed
  - Serialize keyboard backlight notifications
- Reword commit messages and documentations
- Link to v1: https://patch.msgid.link/20260227190617.271388-1-i@rong.moe

---
Rong Zhang (13):
      leds: class: Always protect brightness_show() with led_access
      leds: trigger: Move led_trigger_is_hw_controlled() to the right place
      leds: class: Remove hardware control trigger when writing brightness
      leds: trigger: Move led_trigger_group to the right place
      leds: trigger: Add hw_offloaded() callback and provide trigger_may_offload_to_hw attribute
      leds: cros_ec: Implement hw_offloaded() trigger callback
      leds: turris-omnia: Implement hw_offloaded() trigger callback and declare hw_control_trigger
      leds: trigger: netdev: Implement hw_offloaded() callback
      leds: trigger: Enforce strict checks in led_trigger_is_hw_controlled()
      leds: trigger: Add led_trigger_notify_hw_control_changed() interface
      platform/x86: ideapad-laptop: Serialize keyboard backlight tracking
      platform/x86: ideapad-laptop: Decouple hardware & classdev brightness for keyboard backlight
      platform/x86: ideapad-laptop: Fully support auto keyboard backlight

 Documentation/ABI/testing/sysfs-class-led          |  28 ++-
 .../ABI/testing/sysfs-class-led-trigger-netdev     |   3 +
 Documentation/leds/leds-class.rst                  |  72 ++++++
 drivers/leds/led-class.c                           |  46 ++--
 drivers/leds/led-triggers.c                        | 177 ++++++++++++-
 drivers/leds/leds-cros_ec.c                        |   6 +
 drivers/leds/leds-turris-omnia.c                   |   7 +
 drivers/leds/leds.h                                |   8 +-
 drivers/leds/trigger/Kconfig                       |  10 +
 drivers/leds/trigger/ledtrig-netdev.c              |   8 +
 drivers/platform/x86/lenovo/Kconfig                |   1 +
 drivers/platform/x86/lenovo/ideapad-laptop.c       | 279 +++++++++++++++++----
 include/linux/leds.h                               |  24 ++
 13 files changed, 570 insertions(+), 99 deletions(-)
---
base-commit: 518e5b794c06c0f0eb40df3e202274a66202c137
change-id: 20260506-leds-trigger-hw-changed-96a62188cbdf

Thanks,
Rong

[PATCH v7 01/13] leds: class: Always protect brightness_show() with led_access

[Rong Zhang]

The led_classdev_register_ext() protects transient states when
registering with the led_access mutex and relies on all sensitive sysfs
attribute callbacks holding the mutex to prevent exposing transient
states.

The Fixes: commit broke this as it accessed trigger_lock without holding
led_access. Fix it by protecting brightness_show() with led_access in
all code paths.

Fixes: b819dc7d8fb2 ("leds: core: Report ENODATA for brightness of hardware controlled LED")
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v6:
- New patch in the series to address a concern from Sashiko
  - https://sashiko.dev/#/patchset/20260821-leds-trigger-hw-changed-v5-0-3e00d6c4a936@rong.moe?part=7
---
 drivers/leds/led-class.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index a51b0ed53886..4259533dafa1 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -43,13 +43,13 @@ static ssize_t brightness_show(struct device *dev,
 	struct led_classdev *led_cdev = dev_get_drvdata(dev);
 	unsigned int brightness;
 
-	if (led_trigger_is_hw_controlled(led_cdev))
-		return -ENODATA;
+	scoped_guard(mutex, &led_cdev->led_access) {
+		if (led_trigger_is_hw_controlled(led_cdev))
+			return -ENODATA;
 
-	mutex_lock(&led_cdev->led_access);
-	led_update_brightness(led_cdev);
-	brightness = led_cdev->brightness;
-	mutex_unlock(&led_cdev->led_access);
+		led_update_brightness(led_cdev);
+		brightness = led_cdev->brightness;
+	}
 
 	return sysfs_emit(buf, "%u\n", brightness);
 }

-- 
2.55.0

[PATCH v7 02/13] leds: trigger: Move led_trigger_is_hw_controlled() to the right place

[Rong Zhang]

Currently led_trigger_is_hw_controlled() is placed at led-class.c, which
is not an right place as it falls into the triggers namespace and does
triggers stuff.

Move it into led-triggers.c, and split it into locked and unlocked
variant for convenience.

Fixes: b819dc7d8fb2 ("leds: core: Report ENODATA for brightness of hardware controlled LED")
Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v3:
- New patch in the series, the dependency of the following patches
---
 drivers/leds/led-class.c    | 10 ----------
 drivers/leds/led-triggers.c | 19 +++++++++++++++++++
 include/linux/leds.h        |  8 ++++++++
 3 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 4259533dafa1..7110bfbe3b83 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -27,16 +27,6 @@ static LIST_HEAD(leds_lookup_list);
 
 static struct workqueue_struct *leds_wq;
 
-static bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
-{
-#ifdef CONFIG_LEDS_TRIGGERS
-	guard(rwsem_read)(&led_cdev->trigger_lock);
-	return led_cdev->trigger && led_cdev->trigger->trigger_type;
-#else
-	return false;
-#endif
-}
-
 static ssize_t brightness_show(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index b1223218bda1..bf2543538ed0 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -7,9 +7,11 @@
  * Author: Richard Purdie <rpurdie@openedhand.com>
  */
 
+#include <linux/cleanup.h>
 #include <linux/export.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
+#include <linux/lockdep.h>
 #include <linux/spinlock.h>
 #include <linux/device.h>
 #include <linux/timer.h>
@@ -33,6 +35,23 @@ trigger_relevant(struct led_classdev *led_cdev, struct led_trigger *trig)
 	return !trig->trigger_type || trig->trigger_type == led_cdev->trigger_type;
 }
 
+static bool __led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
+{
+	lockdep_assert_held(&led_cdev->trigger_lock);
+
+	if (!led_cdev->trigger)
+		return false;
+
+	return led_cdev->trigger->trigger_type;
+}
+
+bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
+{
+	guard(rwsem_read)(&led_cdev->trigger_lock);
+	return __led_trigger_is_hw_controlled(led_cdev);
+}
+EXPORT_SYMBOL_GPL(led_trigger_is_hw_controlled);
+
 ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
 			  const struct bin_attribute *bin_attr, char *buf,
 			  loff_t pos, size_t count)
diff --git a/include/linux/leds.h b/include/linux/leds.h
index a515f075c29a..46ad2e03e1c6 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -534,6 +534,8 @@ void led_trigger_set_default(struct led_classdev *led_cdev);
 int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trigger);
 void led_trigger_remove(struct led_classdev *led_cdev);
 
+bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev);
+
 static inline void led_set_trigger_data(struct led_classdev *led_cdev,
 					void *trigger_data)
 {
@@ -584,6 +586,12 @@ static inline int led_trigger_set(struct led_classdev *led_cdev,
 }
 
 static inline void led_trigger_remove(struct led_classdev *led_cdev) {}
+
+static inline bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
+{
+	return false;
+}
+
 static inline void led_set_trigger_data(struct led_classdev *led_cdev) {}
 static inline void *led_get_trigger_data(struct led_classdev *led_cdev)
 {

-- 
2.55.0

[PATCH v7 03/13] leds: class: Remove hardware control trigger when writing brightness

[Rong Zhang]

Since commit b819dc7d8fb2 ("leds: core: Report ENODATA for brightness of
hardware controlled LED"), the brightness attribute becomes write-only
when the LED is controlled fully by the hardware. A write-only attribute
is very confusing.

Moreover, most LED drivers set hardware brightness innocently with the
side effect of disabling hardware control, but the hardware control
trigger remains active, resulting in the software and hardware being out
of sync.

Fix it by removing the hardware control trigger when writing the
brightness attribute.

This should also match the semantics of hardware control:

    When the LED is in hw control, no software blink is possible and
    doing so will effectively disable hw control.

Fixes: b819dc7d8fb2 ("leds: core: Report ENODATA for brightness of hardware controlled LED")
Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v3:
- New patch in the series, integrated from https://lore.kernel.org/all/20260712-leds-hw-control-brightness-set-v1-1-1de593b09d26@rong.moe/
  - The following patches will improve __led_trigger_is_hw_controlled()
    to include offloaded generic triggers and take the advantage of it
---
 Documentation/ABI/testing/sysfs-class-led | 4 +++-
 drivers/leds/led-class.c                  | 3 +++
 drivers/leds/led-triggers.c               | 9 +++++++++
 include/linux/leds.h                      | 2 ++
 4 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
index d4c918cc11a1..f6d4e17e1a3b 100644
--- a/Documentation/ABI/testing/sysfs-class-led
+++ b/Documentation/ABI/testing/sysfs-class-led
@@ -28,7 +28,9 @@ Description:
 		Writing 0 to this file clears active trigger.
 
 		Writing non-zero to this file while trigger is active changes the
-		top brightness trigger is going to use.
+		top brightness trigger is going to use, unless the current
+		trigger is offloaded to hardware (in which case writing any
+		value will deactivate the trigger).
 
 
 
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 7110bfbe3b83..39cc2f3ea63f 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -64,6 +64,9 @@ static ssize_t brightness_store(struct device *dev,
 
 	if (state == LED_OFF)
 		led_trigger_remove(led_cdev);
+	else
+		led_trigger_remove_hw_control(led_cdev);
+
 	led_set_brightness(led_cdev, state);
 
 	ret = size;
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index bf2543538ed0..804a04b326c4 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -287,6 +287,15 @@ void led_trigger_remove(struct led_classdev *led_cdev)
 }
 EXPORT_SYMBOL_GPL(led_trigger_remove);
 
+void led_trigger_remove_hw_control(struct led_classdev *led_cdev)
+{
+	guard(rwsem_write)(&led_cdev->trigger_lock);
+
+	if (__led_trigger_is_hw_controlled(led_cdev))
+		led_trigger_set(led_cdev, NULL);
+}
+EXPORT_SYMBOL_GPL(led_trigger_remove_hw_control);
+
 static bool led_match_default_trigger(struct led_classdev *led_cdev,
 				      struct led_trigger *trig)
 {
diff --git a/include/linux/leds.h b/include/linux/leds.h
index 46ad2e03e1c6..d778709f5b1b 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -533,6 +533,7 @@ void led_trigger_blink_oneshot(struct led_trigger *trigger,
 void led_trigger_set_default(struct led_classdev *led_cdev);
 int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trigger);
 void led_trigger_remove(struct led_classdev *led_cdev);
+void led_trigger_remove_hw_control(struct led_classdev *led_cdev);
 
 bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev);
 
@@ -586,6 +587,7 @@ static inline int led_trigger_set(struct led_classdev *led_cdev,
 }
 
 static inline void led_trigger_remove(struct led_classdev *led_cdev) {}
+static inline void led_trigger_remove_hw_control(struct led_classdev *led_cdev) {}
 
 static inline bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
 {

-- 
2.55.0

[PATCH v7 04/13] leds: trigger: Move led_trigger_group to the right place

[Rong Zhang]

Currently led_trigger_group and its members are placed at led-class.c,
but they falls into the triggers namespace and does triggers stuff.
Placing them at led-class.c also requires the read and write callback to
be exported and results in an extra #ifdef block.

Move it into led-triggers.c, so that it becomes the only symbol to be
exported for sysfs attributes.

Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Add a new patch to the series to collect trigger attribute stuff
  together into led-triggers.c (thanks Lee Jones)
---
 drivers/leds/led-class.c    | 11 -----------
 drivers/leds/led-triggers.c | 25 +++++++++++++++++--------
 drivers/leds/leds.h         |  7 +------
 3 files changed, 18 insertions(+), 25 deletions(-)

diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 39cc2f3ea63f..7f51715fac69 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -90,17 +90,6 @@ static ssize_t max_brightness_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(max_brightness);
 
-#ifdef CONFIG_LEDS_TRIGGERS
-static const BIN_ATTR(trigger, 0644, led_trigger_read, led_trigger_write, 0);
-static const struct bin_attribute *const led_trigger_bin_attrs[] = {
-	&bin_attr_trigger,
-	NULL,
-};
-static const struct attribute_group led_trigger_group = {
-	.bin_attrs = led_trigger_bin_attrs,
-};
-#endif
-
 static struct attribute *led_class_attrs[] = {
 	&dev_attr_brightness.attr,
 	&dev_attr_max_brightness.attr,
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 804a04b326c4..de6056bc80e6 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -52,9 +52,9 @@ bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
 }
 EXPORT_SYMBOL_GPL(led_trigger_is_hw_controlled);
 
-ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
-			  const struct bin_attribute *bin_attr, char *buf,
-			  loff_t pos, size_t count)
+static ssize_t trigger_write(struct file *filp, struct kobject *kobj,
+			     const struct bin_attribute *bin_attr, char *buf,
+			     loff_t pos, size_t count)
 {
 	struct device *dev = kobj_to_dev(kobj);
 	struct led_classdev *led_cdev = dev_get_drvdata(dev);
@@ -97,7 +97,6 @@ ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
 	mutex_unlock(&led_cdev->led_access);
 	return ret;
 }
-EXPORT_SYMBOL_GPL(led_trigger_write);
 
 __printf(3, 4)
 static int led_trigger_snprintf(char *buf, ssize_t size, const char *fmt, ...)
@@ -149,9 +148,9 @@ static int led_trigger_format(char *buf, size_t size,
  * attribute, which is not limited by length. This is _not_ good design, do not
  * copy it.
  */
-ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
-			const struct bin_attribute *attr, char *buf,
-			loff_t pos, size_t count)
+static ssize_t trigger_read(struct file *filp, struct kobject *kobj,
+			    const struct bin_attribute *attr, char *buf,
+			    loff_t pos, size_t count)
 {
 	struct device *dev = kobj_to_dev(kobj);
 	struct led_classdev *led_cdev = dev_get_drvdata(dev);
@@ -179,7 +178,17 @@ ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
 
 	return len;
 }
-EXPORT_SYMBOL_GPL(led_trigger_read);
+static const BIN_ATTR_RW(trigger, 0);
+
+static const struct bin_attribute *const led_trigger_bin_attrs[] = {
+	&bin_attr_trigger,
+	NULL
+};
+
+const struct attribute_group led_trigger_group = {
+	.bin_attrs = led_trigger_bin_attrs,
+};
+EXPORT_SYMBOL_GPL(led_trigger_group);
 
 /* Caller must ensure led_cdev->trigger_lock held */
 int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
diff --git a/drivers/leds/leds.h b/drivers/leds/leds.h
index bee46651e068..c1db21e943b0 100644
--- a/drivers/leds/leds.h
+++ b/drivers/leds/leds.h
@@ -21,14 +21,9 @@ void led_init_core(struct led_classdev *led_cdev);
 void led_stop_software_blink(struct led_classdev *led_cdev);
 void led_set_brightness_nopm(struct led_classdev *led_cdev, unsigned int value);
 void led_set_brightness_nosleep(struct led_classdev *led_cdev, unsigned int value);
-ssize_t led_trigger_read(struct file *filp, struct kobject *kobj,
-			const struct bin_attribute *attr, char *buf,
-			loff_t pos, size_t count);
-ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
-			const struct bin_attribute *bin_attr, char *buf,
-			loff_t pos, size_t count);
 
 extern struct rw_semaphore leds_list_lock;
 extern struct list_head leds_list;
+extern const struct attribute_group led_trigger_group;
 
 #endif	/* __LEDS_H_INCLUDED */

-- 
2.55.0

[PATCH v7 05/13] leds: trigger: Add hw_offloaded() callback and provide trigger_may_offload_to_hw attribute

[Rong Zhang]

There are multiple triggers implementing hardware control. However, the
LED trigger core doesn't really know the hardware control (offloaded)
state since the coordination is done directly between the trigger and
the LED driver. It can only assume private triggers as offloaded and
generic ones as not offloaded.

Add an hw_offloaded() callback so that triggers can report their
offloaded states to the LED trigger core. When unimplemented, it
defaults to true for private triggers and false for generic ones to keep
the current behavior unchanged.

With that, provide a new attribute "trigger_may_offload_to_hw", so that
userspace can determine:

- if the LED device supports hardware control (supported => visible)
- which trigger is the hardware control trigger selected by the LED
  device and offloaded to hardware ("[foo_trigger]")

Note: the documentation describes the attribute as "returning a list"
despite the LED core currently only supports one hardware control
trigger per LED device. This is intentional to make the attribute
extensible in the future without breaking userspace. IOW, userspace
should parse the new attribute in the same way as
/sys/class/leds/<led>/trigger.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Leave all attribute stuff at led-triggers.c (thanks Lee Jones)
- Rename the offloaded() callback to hw_offloaded() (ditto)
- Rename the trigger_may_offload attribute to
  trigger_may_offload_to_hw (ditto)
- Use "[foo_trigger]" to represent a selected and offloaded trigger, and
  no longer use a dedicated container to represent selected but not
  offloaded ones (ditto)
  - In this commit, the trigger_may_offload_to_hw_show() callback does
    not match the current trigger's name against hw_control_trigger yet.
    The check will be added in a later commit once all relevant LED
    drivers have properly declared hw_control_trigger and LED triggers
    have implemented hw_offloaded()
  - For now, only "netdev" and "chromeos-auto" have associated LED
    drivers, which expose the new attribute. The former is always
    reproted as not offloaded in this commit, while a later commit will
    implement hw_offloaded() to properly provide the offloaded state.
    The latter's associated driver's only private trigger is exactly
    "chromeos-auto", which is always correctly reported as offloaded in
    this commit
  - All private triggers will gain hw_offloaded() and their associated
    LED drivers will gain hw_control_trigger in later commits, so that
    they can provide the attribute properly
- Constify device attribute trigger_may_offload_to_hw

Changes in v6:
- Update Date: and KernelVersion: for the document of
  /sys/class/leds/<led>/trigger_may_offload

Changes in v3:
- Rearrange the series so that the code using the offloaded() callback is
  introduced before the driver implementation (thanks Thomas Weißschuh)
- Reword documentation (ditto)
- Adopt guard() and lockdep (ditto)
- Adopt __led_trigger_is_hw_controlled() from newly-integrated PATCH 1
---
 Documentation/ABI/testing/sysfs-class-led | 21 ++++++++++++++++++
 Documentation/leds/leds-class.rst         | 20 +++++++++++++++++
 drivers/leds/led-triggers.c               | 36 +++++++++++++++++++++++++++++++
 include/linux/leds.h                      |  1 +
 4 files changed, 78 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
index f6d4e17e1a3b..123e3a15b7d6 100644
--- a/Documentation/ABI/testing/sysfs-class-led
+++ b/Documentation/ABI/testing/sysfs-class-led
@@ -80,6 +80,27 @@ Description:
 		(which would often be configured in the device tree for the
 		hardware).
 
+What:		/sys/class/leds/<led>/trigger_may_offload_to_hw
+Date:		September 2026
+KernelVersion:	7.4
+Contact:	linux-leds@vger.kernel.org
+Description:
+		Names and states of triggers that may be offloaded to hardware.
+		Such triggers are also called "hardware control trigger" in some
+		context.
+
+		Only exists when the LED supports trigger offload.
+
+		Reading this file returns a list of triggers that are capable to
+		be offloaded. The optional brackets around the trigger name
+		indicate the state of the current trigger:
+
+		- `foo_trigger`: the trigger is not selected, or selected but
+		  falls back to software blink for some reasons, e.g.,
+		  incompatible trigger parameters.
+		- `[foo_trigger]`: the trigger is selected and offloaded to
+		  hardware.
+
 What:		/sys/class/leds/<led>/inverted
 Date:		January 2011
 KernelVersion:	2.6.38
diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
index 3913966cfdac..ea478989aae2 100644
--- a/Documentation/leds/leds-class.rst
+++ b/Documentation/leds/leds-class.rst
@@ -242,6 +242,9 @@ ops and needs to declare specific support for the supported triggers.
 
 With hw control we refer to the LED driven by hardware.
 
+A sysfs attribute `trigger_may_offload_to_hw` is provided for userspace
+to query supported triggers and their states.
+
 LED driver must define the following value to support hw control:
 
     - hw_control_trigger:
@@ -298,6 +301,15 @@ LED driver must implement the following API to support hw control:
                 Returns a pointer to a struct device or NULL if nothing
                 is currently attached.
 
+LED trigger should implement the following API to indicate hw control:
+    - hw_offloaded:
+                return a boolean indicating if the trigger is currently
+                offloaded to hardware.
+
+                If a trigger doesn't implement this callback, the default
+                value will be true for private triggers and false for generic
+                ones.
+
 LED driver can activate additional modes by default to workaround the
 impossibility of supporting each different mode on the supported trigger.
 Examples are hardcoding the blink speed to a set interval, enable special
@@ -311,6 +323,14 @@ the end use hw_control_set to activate hw control.
 A trigger can use hw_control_get to check if a LED is already in hw control
 and init their flags.
 
+Alternatively, a private trigger can be implemented along with the LED driver if
+the LED's hardware control doesn't fit any generic trigger. To associate the
+private trigger with the LED classdev, their `trigger_type` must be the same. To
+declare that the private trigger provides hardware control for the associated
+LED classdev, set the `hw_control_trigger` string to the trigger's name. Since
+both the LED classdev and the private trigger are in the same LED driver, it's
+not necessary for them to coordinate via `hw_control_*` callbacks.
+
 When the LED is in hw control, no software blink is possible and doing so
 will effectively disable hw control.
 
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index de6056bc80e6..38ce3350c870 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -42,6 +42,10 @@ static bool __led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
 	if (!led_cdev->trigger)
 		return false;
 
+	if (led_cdev->trigger->hw_offloaded)
+		return led_cdev->trigger->hw_offloaded(led_cdev);
+
+	/* Otherwise assume private triggers are always offloaded. */
 	return led_cdev->trigger->trigger_type;
 }
 
@@ -185,8 +189,40 @@ static const struct bin_attribute *const led_trigger_bin_attrs[] = {
 	NULL
 };
 
+static ssize_t trigger_may_offload_to_hw_show(struct device *dev,
+					      const struct device_attribute *attr, char *buf)
+{
+	struct led_classdev *led_cdev = dev_get_drvdata(dev);
+	bool offloaded = led_trigger_is_hw_controlled(led_cdev);
+
+	return sysfs_emit(buf, "%s%s%s\n",
+			  offloaded ? "[" : "",
+			  led_cdev->hw_control_trigger,
+			  offloaded ? "]" : "");
+}
+static const DEVICE_ATTR_RO(trigger_may_offload_to_hw);
+
+static const struct attribute *const led_trigger_attrs[] = {
+	&dev_attr_trigger_may_offload_to_hw.attr,
+	NULL
+};
+
+static umode_t led_trigger_is_visible(struct kobject *kobj,
+				      const struct attribute *attr, int idx)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct led_classdev *led_cdev = dev_get_drvdata(dev);
+
+	if (attr == &dev_attr_trigger_may_offload_to_hw.attr)
+		return led_cdev->hw_control_trigger ? attr->mode : 0;
+
+	return attr->mode;
+}
+
 const struct attribute_group led_trigger_group = {
 	.bin_attrs = led_trigger_bin_attrs,
+	.attrs_const = led_trigger_attrs,
+	.is_visible_const = led_trigger_is_visible,
 };
 EXPORT_SYMBOL_GPL(led_trigger_group);
 
diff --git a/include/linux/leds.h b/include/linux/leds.h
index d778709f5b1b..9a0bfd985b46 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -485,6 +485,7 @@ struct led_trigger {
 	const char	 *name;
 	int		(*activate)(struct led_classdev *led_cdev);
 	void		(*deactivate)(struct led_classdev *led_cdev);
+	bool		(*hw_offloaded)(struct led_classdev *led_cdev);
 
 	/* Brightness set by led_trigger_event */
 	enum led_brightness brightness;

-- 
2.55.0

[PATCH v7 06/13] leds: cros_ec: Implement hw_offloaded() trigger callback

[Rong Zhang]

"chromeos-auto" is a private hardware control trigger which always stays
in hardware control. Implement hw_offloaded() callback with its return
value to be always true to reflect this.

Reviewed-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Rename the offloaded() callback to hw_offloaded() (thanks Lee Jones)
---
 drivers/leds/leds-cros_ec.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/leds/leds-cros_ec.c b/drivers/leds/leds-cros_ec.c
index 1844d0cd5f52..0e93aa28a8b1 100644
--- a/drivers/leds/leds-cros_ec.c
+++ b/drivers/leds/leds-cros_ec.c
@@ -85,12 +85,18 @@ static int cros_ec_led_trigger_activate(struct led_classdev *led_cdev)
 	return cros_ec_led_send_cmd(priv->cros_ec, &arg);
 }
 
+static bool cros_ec_led_trigger_hw_offloaded(struct led_classdev *led_cdev)
+{
+	return true;
+}
+
 static struct led_hw_trigger_type cros_ec_led_trigger_type;
 
 static struct led_trigger cros_ec_led_trigger = {
 	.name = "chromeos-auto",
 	.trigger_type = &cros_ec_led_trigger_type,
 	.activate = cros_ec_led_trigger_activate,
+	.hw_offloaded = cros_ec_led_trigger_hw_offloaded,
 };
 
 static int cros_ec_led_brightness_set_blocking(struct led_classdev *led_cdev,

-- 
2.55.0

[PATCH v7 07/13] leds: turris-omnia: Implement hw_offloaded() trigger callback and declare hw_control_trigger

[Rong Zhang]

"omnia-mcu" is a private hardware control trigger which always stays in
hardware control mode. Implement hw_offloaded() callback with its return
value to be always true to reflect this.

Meanwhile, declare it as a hardware control trigger as it's forgotten
before.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Rename the offloaded() callback to hw_offloaded() (thanks Lee Jones)
---
 drivers/leds/leds-turris-omnia.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/leds/leds-turris-omnia.c b/drivers/leds/leds-turris-omnia.c
index ed6a47bbb44f..57128ae7e8fd 100644
--- a/drivers/leds/leds-turris-omnia.c
+++ b/drivers/leds/leds-turris-omnia.c
@@ -195,10 +195,16 @@ static void omnia_hwtrig_deactivate(struct led_classdev *cdev)
 			err);
 }
 
+static bool omnia_hwtrig_hw_offloaded(struct led_classdev *cdev)
+{
+	return true;
+}
+
 static struct led_trigger omnia_hw_trigger = {
 	.name		= "omnia-mcu",
 	.activate	= omnia_hwtrig_activate,
 	.deactivate	= omnia_hwtrig_deactivate,
+	.hw_offloaded	= omnia_hwtrig_hw_offloaded,
 	.trigger_type	= &omnia_hw_trigger_type,
 };
 
@@ -251,6 +257,7 @@ static int omnia_led_register(struct i2c_client *client, struct omnia_led *led,
 	 * by LED class from the linux,default-trigger property.
 	 */
 	cdev->default_trigger = omnia_hw_trigger.name;
+	cdev->hw_control_trigger = omnia_hw_trigger.name;
 
 	/* Put the LED into software mode */
 	ret = omnia_cmd_write_u8(client, OMNIA_CMD_LED_MODE, OMNIA_CMD_LED_MODE_LED(led->reg) |

-- 
2.55.0

[PATCH v7 08/13] leds: trigger: netdev: Implement hw_offloaded() callback

[Rong Zhang]

"netdev" can run in hardware control according to hardware capabilities
and trigger options.

Implement hw_offloaded() callback to provide its hardware control state
to the LED core, and document the relation between the custom
"offloaded" attribute and the generic "trigger_may_offload_to_hw"
attribute.

The callback mimics how the existing "offloaded" attribute does, i.e.,
locklessly reads hw_control, as it's just a hint and don't need to be
accurate.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Rename the offloaded() callback to hw_offloaded() (thanks Lee Jones)
- Rename the trigger_may_offload attribute to
  trigger_may_offload_to_hw (ditto)

Changes in v3:
- Do not deprecate netdev's "offloaded" attribute (thanks Thomas
  Weißschuh)
- Document the relation between the custom "offloaded" attribute and the
  generic "trigger_may_offload" attribute (ditto)
---
 Documentation/ABI/testing/sysfs-class-led                | 3 +++
 Documentation/ABI/testing/sysfs-class-led-trigger-netdev | 3 +++
 drivers/leds/trigger/ledtrig-netdev.c                    | 8 ++++++++
 3 files changed, 14 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
index 123e3a15b7d6..ea113fed10ef 100644
--- a/Documentation/ABI/testing/sysfs-class-led
+++ b/Documentation/ABI/testing/sysfs-class-led
@@ -101,6 +101,9 @@ Description:
 		- `[foo_trigger]`: the trigger is selected and offloaded to
 		  hardware.
 
+		The "netdev" trigger also provides a custom attribute to
+		indicate its state, see `/sys/class/leds/<led>/offloaded`.
+
 What:		/sys/class/leds/<led>/inverted
 Date:		January 2011
 KernelVersion:	2.6.38
diff --git a/Documentation/ABI/testing/sysfs-class-led-trigger-netdev b/Documentation/ABI/testing/sysfs-class-led-trigger-netdev
index ed46b37ab8a2..203ea58396ed 100644
--- a/Documentation/ABI/testing/sysfs-class-led-trigger-netdev
+++ b/Documentation/ABI/testing/sysfs-class-led-trigger-netdev
@@ -75,6 +75,9 @@ Description:
 		If 1, the LED blinking in requested mode is offloaded to
 		hardware.
 
+		LED trigger core also provides a generic attribute for this
+		purpose, see `/sys/class/leds/<led>/trigger_may_offload_to_hw`.
+
 What:		/sys/class/leds/<led>/link_10
 Date:		Jun 2023
 KernelVersion:	6.5
diff --git a/drivers/leds/trigger/ledtrig-netdev.c b/drivers/leds/trigger/ledtrig-netdev.c
index 5b4e92c14dbb..60409f054e22 100644
--- a/drivers/leds/trigger/ledtrig-netdev.c
+++ b/drivers/leds/trigger/ledtrig-netdev.c
@@ -798,10 +798,18 @@ static void netdev_trig_deactivate(struct led_classdev *led_cdev)
 	kfree(trigger_data);
 }
 
+static bool netdev_trig_hw_offloaded(struct led_classdev *led_cdev)
+{
+	struct led_netdev_data *trigger_data = led_get_trigger_data(led_cdev);
+
+	return trigger_data->hw_control;
+}
+
 static struct led_trigger netdev_led_trigger = {
 	.name = "netdev",
 	.activate = netdev_trig_activate,
 	.deactivate = netdev_trig_deactivate,
+	.hw_offloaded = netdev_trig_hw_offloaded,
 	.groups = netdev_trig_groups,
 };
 

-- 
2.55.0

[PATCH v7 09/13] leds: trigger: Enforce strict checks in led_trigger_is_hw_controlled()

[Rong Zhang]

With all existing triggers adopting the new interface, strict checks
could be enforced to make the semantics of hardware control triggers
clearer.

In detail, a hardware control trigger should:

- Implement hw_offloaded() callback to indicate hardware control
- Associate with the LED classdev's hw_control_trigger string

The fallback path is kept, but a warning message is emitted when it
reaches there.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Rename the offloaded() callback to hw_offloaded() (thanks Lee Jones)

Changes in v3:
- New patch in the series, splitted from PATCH 3 (thanks Thomas
  Weißschuh)
---
 drivers/leds/led-triggers.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 38ce3350c870..6fee3145caab 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -42,9 +42,17 @@ static bool __led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
 	if (!led_cdev->trigger)
 		return false;
 
+	if (!led_cdev->hw_control_trigger ||
+	    strcmp(led_cdev->hw_control_trigger, led_cdev->trigger->name))
+		return false;
+
 	if (led_cdev->trigger->hw_offloaded)
 		return led_cdev->trigger->hw_offloaded(led_cdev);
 
+	dev_warn_once(led_cdev->dev,
+		      "Hardware control trigger %s doesn't provide offloaded state\n",
+		      led_cdev->trigger->name);
+
 	/* Otherwise assume private triggers are always offloaded. */
 	return led_cdev->trigger->trigger_type;
 }

-- 
2.55.0

[PATCH v7 10/13] leds: trigger: Add led_trigger_notify_hw_control_changed() interface

[Rong Zhang]

Some hardware can autonomously activate/deactivate hardware control.
After that, the LED hardware notifies the LED driver. Currently, there
is no mechanism for LED drivers to notify the LED core about such events
and initiate a trigger transition to reflect the hardware state.

Add a new interface called led_trigger_notify_hw_control_changed(), so
that LED drivers can call it to notify the LED core about the
transition.

The interface only allows two transitions:

1. "none" => private trigger
2. private trigger => "none"

If the current trigger is neither the private trigger nor "none", no
transition will be made. This protects the currently selected software
trigger.

Note that LED_OFF won't be emitted during the #2 transition, as some
hardware may have selected a new brightness level during its hardware
state transition (e.g., laptop keyboards with a shortcut cycling through
different backlight brightnesses and auto mode).

The interface is designed as a void function as any failure should be
non-fatal and the result of transition should not have any impact on the
LED drivers' event handling procedures.

To use the interface, the config LEDS_TRIGGERS_HW_CHANGED must be
enabled, and the LED driver must set the LED_TRIG_HW_CHANGED flag for
the classdev.

By default, the config is enabled when LEDS_BRIGHTNESS_HW_CHANGED is
enabled.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Remove messages mainly for debugging (thanks Lee Jones)
- Inline led_trigger_{init,destroy}_hw_changed() into led-class.c by
  exporting led_trigger_hw_control_changed_worker() (ditto)
- Rephrase some comments and messages (ditto)

Changes in v6:
- Implement workqueue deferal mechanism
  - https://msgid.link/e2b081dfd8f96511a73b86ab3ec75e5cd759b79b.camel@rong.moe

Changes in v5:
- Address a concern from Sashiko:
  - led_trigger_notify_hw_control_changed() might sleep, but without any
    internal deferral mechanism or annotation
  - Annotate the method with might_sleep(), since the very first users
    of the interface, i.e., ideapad-laptop and (supposedly)
    thinkpad_acpi, will call the interface from work contexts. It does
    not deserve the overhead of internal deferral mechanism
  - https://sashiko.dev/#/patchset/20260802-leds-trigger-hw-changed-v4-0-f97e2ca976fe@rong.moe?part=9

Changes in v4:
- Enable LEDS_TRIGGERS_HW_CHANGED by default when
  LEDS_BRIGHTNESS_HW_CHANGED is enabled

Changes in v3:
- Adopt guard() (Thanks Thomas Weißschuh)
- Reword documentations
---
 Documentation/leds/leds-class.rst | 52 +++++++++++++++++++++++++
 drivers/leds/led-class.c          | 10 +++++
 drivers/leds/led-triggers.c       | 80 ++++++++++++++++++++++++++++++++++++++-
 drivers/leds/leds.h               |  1 +
 drivers/leds/trigger/Kconfig      | 10 +++++
 include/linux/leds.h              | 13 +++++++
 6 files changed, 164 insertions(+), 2 deletions(-)

diff --git a/Documentation/leds/leds-class.rst b/Documentation/leds/leds-class.rst
index ea478989aae2..464e54cabf52 100644
--- a/Documentation/leds/leds-class.rst
+++ b/Documentation/leds/leds-class.rst
@@ -334,6 +334,58 @@ not necessary for them to coordinate via `hw_control_*` callbacks.
 When the LED is in hw control, no software blink is possible and doing so
 will effectively disable hw control.
 
+Hardware-initiated trigger transition
+=====================================
+
+Some hardware can autonomously activate/deactivate hardware control. After that,
+the LED hardware notifies the LED driver.
+
+If the driver can detect such transitions and thus wants to notify the LED core
+to update the current trigger then the `LED_TRIG_HW_CHANGED` flag must be set in
+flags before registering. To update the current trigger accordingly, call
+`led_trigger_notify_hw_control_changed` on the LED classdev.
+
+This capability is restricted to the LED device's private trigger. The private
+trigger must have been properly registered (see above) and named after
+`hw_control_trigger`.
+
+Only two transitions are defined:
+
+- "none" => private trigger:
+        This happens when the hardware autonomously activates hardware control
+        and when "none" (i.e., no trigger) is currently active. If the private
+        trigger is already active when the method is called, this is essentially
+        a no-op.
+
+        The activation sequence for the private trigger will be executed as
+        normal.
+
+        The LED driver and its private trigger must be able to handle the
+        activation sequence even if the hardware is currently in hardware
+        control.
+
+        If error occurs in the activation sequence, the LED Trigger core reverts
+        the effective trigger to "none".
+
+- private trigger => "none"
+        This happens when the hardware autonomously deactivates hardware control
+        and when the private trigger is currently active. If "none" (i.e., no
+        trigger) is active when the method is called, this is essentially a
+        no-op.
+
+        The deactivation sequence for the private trigger will be executed as
+        normal, except that the current LED brightness is retained. The reason
+        for keeping the brightness unchanged is that some hardware may choose a
+        specific brightness instead of simply turning off the LED after
+        autonomously deactivating hardware control.
+
+        The LED driver and its private trigger must be able to handle the
+        deactivation sequence even if the hardware is not currently in hardware
+        control.
+
+If the current trigger is neither the private trigger nor "none", no transition
+will be made.
+
 Known Issues
 ============
 
diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
index 7f51715fac69..00be3cb96c00 100644
--- a/drivers/leds/led-class.c
+++ b/drivers/leds/led-class.c
@@ -559,6 +559,11 @@ int led_classdev_register_ext(struct device *parent,
 #endif
 #ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED
 	led_cdev->brightness_hw_changed = -1;
+#endif
+#ifdef CONFIG_LEDS_TRIGGERS_HW_CHANGED
+	if (led_cdev->flags & LED_TRIG_HW_CHANGED)
+		INIT_WORK(&led_cdev->trigger_hw_changed_work,
+			  led_trigger_hw_control_changed_worker);
 #endif
 	if (!led_cdev->max_brightness)
 		led_cdev->max_brightness = LED_FULL;
@@ -598,6 +603,11 @@ void led_classdev_unregister(struct led_classdev *led_cdev)
 	if (IS_ERR_OR_NULL(led_cdev->dev))
 		return;
 
+#ifdef CONFIG_LEDS_TRIGGERS_HW_CHANGED
+	if (led_cdev->flags & LED_TRIG_HW_CHANGED)
+		disable_work_sync(&led_cdev->trigger_hw_changed_work);
+#endif
+
 #ifdef CONFIG_LEDS_TRIGGERS
 	down_write(&led_cdev->trigger_lock);
 	if (led_cdev->trigger)
diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
index 6fee3145caab..f16603b5ff44 100644
--- a/drivers/leds/led-triggers.c
+++ b/drivers/leds/led-triggers.c
@@ -7,7 +7,9 @@
  * Author: Richard Purdie <rpurdie@openedhand.com>
  */
 
+#include <linux/bug.h>
 #include <linux/cleanup.h>
+#include <linux/compiler.h>
 #include <linux/export.h>
 #include <linux/kernel.h>
 #include <linux/list.h>
@@ -235,7 +237,8 @@ const struct attribute_group led_trigger_group = {
 EXPORT_SYMBOL_GPL(led_trigger_group);
 
 /* Caller must ensure led_cdev->trigger_lock held */
-int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
+static int __led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig,
+			     bool hw_triggered)
 {
 	char *event = NULL;
 	char *envp[2];
@@ -266,7 +269,21 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 		led_cdev->trigger_data = NULL;
 		led_cdev->activated = false;
 		led_cdev->flags &= ~LED_INIT_DEFAULT_TRIGGER;
-		led_set_brightness(led_cdev, LED_OFF);
+
+		/*
+		 * Hardware may have selected a new brightness level during its
+		 * hardware control transition, so only reset brightness if we
+		 * are switching to another trigger or if the switching is not
+		 * hardware triggered.
+		 *
+		 * Note that this does not apply to the error path, as running
+		 * into the error path implies a none => private trigger
+		 * transition. This hints that the LED driver and its private
+		 * trigger must have some fundamental bugs, so the error path
+		 * always turns off the LED to reset it to a certain state.
+		 */
+		if (trig || !hw_triggered)
+			led_set_brightness(led_cdev, LED_OFF);
 	}
 	if (trig) {
 		spin_lock(&trig->leddev_list_lock);
@@ -330,6 +347,11 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
 
 	return ret;
 }
+
+int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
+{
+	return __led_trigger_set(led_cdev, trig, false);
+}
 EXPORT_SYMBOL_GPL(led_trigger_set);
 
 void led_trigger_remove(struct led_classdev *led_cdev)
@@ -484,6 +506,60 @@ int devm_led_trigger_register(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(devm_led_trigger_register);
 
+#ifdef CONFIG_LEDS_TRIGGERS_HW_CHANGED
+
+static void led_trigger_do_hw_control_transition(struct led_classdev *led_cdev, bool activate,
+						 struct led_trigger *hc_trig)
+{
+	if (activate && !led_cdev->trigger) /* "none" => private trigger. */
+		__led_trigger_set(led_cdev, hc_trig, true);
+	else if (!activate && led_cdev->trigger == hc_trig) /* private trigger => "none". */
+		__led_trigger_set(led_cdev, NULL, true);
+
+	/* Already in the desired state, or another trigger is active, ignore. */
+}
+
+void led_trigger_hw_control_changed_worker(struct work_struct *work)
+{
+	struct led_classdev *led_cdev =
+		container_of(work, struct led_classdev, trigger_hw_changed_work);
+	bool activate = READ_ONCE(led_cdev->trigger_hw_changed);
+
+	scoped_guard(rwsem_read, &triggers_list_lock) {
+		struct led_trigger *trig;
+
+		list_for_each_entry(trig, &trigger_list, next_trig) {
+			if (trig->trigger_type == led_cdev->trigger_type &&
+			    !strcmp(trig->name, led_cdev->hw_control_trigger)) {
+				guard(rwsem_write)(&led_cdev->trigger_lock);
+
+				led_trigger_do_hw_control_transition(led_cdev, activate, trig);
+				return;
+			}
+		}
+	}
+
+	dev_warn(led_cdev->dev,
+		 "Private trigger %s is not registered, can't toggle hardware control\n",
+		 led_cdev->hw_control_trigger);
+}
+EXPORT_SYMBOL_GPL(led_trigger_hw_control_changed_worker);
+
+void led_trigger_notify_hw_control_changed(struct led_classdev *led_cdev, bool activate)
+{
+	/* Restricted to private triggers. */
+	if (WARN_ON(!(led_cdev->flags & LED_TRIG_HW_CHANGED) ||
+		    !led_cdev->hw_control_trigger || !led_cdev->trigger_type))
+		return;
+
+	WRITE_ONCE(led_cdev->trigger_hw_changed, activate);
+
+	schedule_work(&led_cdev->trigger_hw_changed_work);
+}
+EXPORT_SYMBOL_GPL(led_trigger_notify_hw_control_changed);
+
+#endif /* CONFIG_LEDS_TRIGGERS_HW_CHANGED */
+
 /* Simple LED Trigger Interface */
 
 void led_trigger_event(struct led_trigger *trig,
diff --git a/drivers/leds/leds.h b/drivers/leds/leds.h
index c1db21e943b0..6d00e6f44126 100644
--- a/drivers/leds/leds.h
+++ b/drivers/leds/leds.h
@@ -21,6 +21,7 @@ void led_init_core(struct led_classdev *led_cdev);
 void led_stop_software_blink(struct led_classdev *led_cdev);
 void led_set_brightness_nopm(struct led_classdev *led_cdev, unsigned int value);
 void led_set_brightness_nosleep(struct led_classdev *led_cdev, unsigned int value);
+void led_trigger_hw_control_changed_worker(struct work_struct *work);
 
 extern struct rw_semaphore leds_list_lock;
 extern struct list_head leds_list;
diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
index c11282a74b5a..a11d04ce4ab2 100644
--- a/drivers/leds/trigger/Kconfig
+++ b/drivers/leds/trigger/Kconfig
@@ -9,6 +9,16 @@ menuconfig LEDS_TRIGGERS
 
 if LEDS_TRIGGERS
 
+config LEDS_TRIGGERS_HW_CHANGED
+	bool "LED hardware-initiated trigger transition support"
+	default LEDS_BRIGHTNESS_HW_CHANGED
+	help
+	  This option enables support for hardware initiated hardware control
+	  transitions, where the LED hardware autonomously switches between
+	  "none" (i.e., no trigger) and its private trigger.
+
+	  See Documentation/leds/leds-class.rst for details.
+
 config LEDS_TRIGGER_TIMER
 	tristate "LED Timer Trigger"
 	help
diff --git a/include/linux/leds.h b/include/linux/leds.h
index 9a0bfd985b46..beaf23993063 100644
--- a/include/linux/leds.h
+++ b/include/linux/leds.h
@@ -109,6 +109,7 @@ struct led_classdev {
 #define LED_INIT_DEFAULT_TRIGGER BIT(23)
 #define LED_REJECT_NAME_CONFLICT BIT(24)
 #define LED_MULTI_COLOR		BIT(25)
+#define LED_TRIG_HW_CHANGED	BIT(26)
 
 	/* set_brightness_work / blink_timer flags, atomic, private. */
 	unsigned long		work_flags;
@@ -239,6 +240,11 @@ struct led_classdev {
 	struct kernfs_node	*brightness_hw_changed_kn;
 #endif
 
+#ifdef CONFIG_LEDS_TRIGGERS_HW_CHANGED
+	bool			trigger_hw_changed;
+	struct work_struct	trigger_hw_changed_work;
+#endif
+
 	/* Ensures consistent access to the LED class device */
 	struct mutex		led_access;
 };
@@ -609,6 +615,13 @@ led_trigger_get_brightness(const struct led_trigger *trigger)
 
 #endif /* CONFIG_LEDS_TRIGGERS */
 
+#ifdef CONFIG_LEDS_TRIGGERS_HW_CHANGED
+void led_trigger_notify_hw_control_changed(struct led_classdev *led_cdev, bool activate);
+#else
+static inline void led_trigger_notify_hw_control_changed(struct led_classdev *led_cdev,
+							 bool activate) {}
+#endif
+
 /* Trigger specific enum */
 enum led_trigger_netdev_modes {
 	TRIGGER_NETDEV_LINK = 0,

-- 
2.55.0

[PATCH v7 11/13] platform/x86: ideapad-laptop: Serialize keyboard backlight tracking

[Rong Zhang]

ACPI notifications are delivered in dedicated work contexts and may
arrive simultaneously. In the following change, much work will be done
while handling the notification, which could lead to potential race
conditions.

Introduce a new mutex to serialize keyboard backlight tracking to
prevent potential race conditions.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v6:
- Protects ideapad_kbd_bl_led_cdev_brightness_set() as well

Changes in v4:
- Remove needless #include (Thanks Ilpo Järvinen)
---
 drivers/platform/x86/lenovo/ideapad-laptop.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/platform/x86/lenovo/ideapad-laptop.c b/drivers/platform/x86/lenovo/ideapad-laptop.c
index 8213524504ee..684421ba53cb 100644
--- a/drivers/platform/x86/lenovo/ideapad-laptop.c
+++ b/drivers/platform/x86/lenovo/ideapad-laptop.c
@@ -26,6 +26,7 @@
 #include <linux/kernel.h>
 #include <linux/leds.h>
 #include <linux/module.h>
+#include <linux/mutex.h>
 #include <linux/platform_device.h>
 #include <linux/platform_profile.h>
 #include <linux/power_supply.h>
@@ -204,6 +205,7 @@ struct ideapad_private {
 		int type;
 		struct led_classdev led;
 		unsigned int last_brightness;
+		struct mutex mutex; /* protects brightness tracking */
 	} kbd_bl;
 	struct {
 		bool initialized;
@@ -1643,6 +1645,8 @@ static int ideapad_kbd_bl_brightness_set(struct ideapad_private *priv, unsigned
 	unsigned long value;
 	int type = priv->kbd_bl.type;
 
+	guard(mutex)(&priv->kbd_bl.mutex);
+
 	if (ideapad_kbd_bl_check_tristate(type)) {
 		if (brightness > priv->kbd_bl.led.max_brightness)
 			return -EINVAL;
@@ -1678,6 +1682,8 @@ static void ideapad_kbd_bl_notify(struct ideapad_private *priv)
 	if (!priv->kbd_bl.initialized)
 		return;
 
+	guard(mutex)(&priv->kbd_bl.mutex);
+
 	brightness = ideapad_kbd_bl_brightness_get(priv);
 	if (brightness < 0)
 		return;
@@ -1700,6 +1706,10 @@ static int ideapad_kbd_bl_init(struct ideapad_private *priv)
 	if (WARN_ON(priv->kbd_bl.initialized))
 		return -EEXIST;
 
+	err = devm_mutex_init(&priv->platform_device->dev, &priv->kbd_bl.mutex);
+	if (err)
+		return err;
+
 	if (ideapad_kbd_bl_check_tristate(priv->kbd_bl.type))
 		priv->kbd_bl.led.max_brightness = 2;
 	else

-- 
2.55.0

[PATCH v7 12/13] platform/x86: ideapad-laptop: Decouple hardware & classdev brightness for keyboard backlight

[Rong Zhang]

Some recent models come with an ambient light sensor (ALS). On these
models, their EC will automatically set the keyboard backlight to an
appropriate brightness when the effective "hardware brightness" is 3.
"Hardware brightness" can't be perfectly mapped to an LED classdev
brightness, but the EC does use this predefined brightness value to
represent auto mode.

Currently, the code processing keyboard backlight is coupled with LED
classdev, making it hard to expose the auto brightness (ALS) mode to the
userspace.

As the first step toward the goal, decouple hardware brightness from LED
classdev brightness, and update comments about corresponding backlight
modes.

To minimalize the diff set in upcoming changes, a trivial refactor
also converts the initialization path into another equivalent form.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Address a concern from Sashiko
  - Fix printf format string
  - https://sashiko.dev/#/patchset/20260902-leds-trigger-hw-changed-v6-0-55693cd78877@rong.moe?part=11

Changes in v6:
- No longer convert last_hw_brightness into atomic_t as it's not
  required now

Changes in v4:
- Add missing #include (Thanks Ilpo Järvinen)
- Address concerns from Sashiko
  - Reject insane hardware brightness
  - https://sashiko.dev/#/patchset/20260719-leds-trigger-hw-changed-v3-0-5fb55722e36e@rong.moe?part=9
---
 drivers/platform/x86/lenovo/ideapad-laptop.c | 150 +++++++++++++++++++--------
 1 file changed, 106 insertions(+), 44 deletions(-)

diff --git a/drivers/platform/x86/lenovo/ideapad-laptop.c b/drivers/platform/x86/lenovo/ideapad-laptop.c
index 684421ba53cb..b57c4f18d0ea 100644
--- a/drivers/platform/x86/lenovo/ideapad-laptop.c
+++ b/drivers/platform/x86/lenovo/ideapad-laptop.c
@@ -14,9 +14,11 @@
 #include <linux/bitops.h>
 #include <linux/bug.h>
 #include <linux/cleanup.h>
+#include <linux/compiler.h>
 #include <linux/debugfs.h>
 #include <linux/delay.h>
 #include <linux/device.h>
+#include <linux/dev_printk.h>
 #include <linux/dmi.h>
 #include <linux/i8042.h>
 #include <linux/init.h>
@@ -135,10 +137,31 @@ enum {
 };
 
 /*
- * These correspond to the number of supported states - 1
- * Future keyboard types may need a new system, if there's a collision
- * KBD_BL_TRISTATE_AUTO has no way to report or set the auto state
- * so it effectively has 3 states, but needs to handle 4
+ * The enumeration has two purposes:
+ *   - as an internal identifier for all known types of keyboard backlight
+ *   - as a mandatory parameter of the KBLC command
+ *
+ * For each type, the hardware brightness values are defined as follows:
+ * +--------------------------+----------+-----+------+------+
+ * |      Hardware brightness |        0 |   1 |    2 |    3 |
+ * | Type                     |          |     |      |      |
+ * +--------------------------+----------+-----+------+------+
+ * | KBD_BL_STANDARD          |      off |  on |  N/A |  N/A |
+ * +--------------------------+----------+-----+------+------+
+ * | KBD_BL_TRISTATE          |      off | low | high |  N/A |
+ * +--------------------------+----------+-----+------+------+
+ * | KBD_BL_TRISTATE_AUTO     |      off | low | high | auto |
+ * +--------------------------+----------+-----+------+------+
+ *
+ * We map LED classdev brightness for KBD_BL_TRISTATE_AUTO as follows:
+ * +--------------------------+----------+-----+------+
+ * |  LED classdev brightness |        0 |   1 |    2 |
+ * | Operation                |          |     |      |
+ * +--------------------------+----------+-----+------+
+ * | Read                     | off/auto | low | high |
+ * +--------------------------+----------+-----+------+
+ * | Write                    |      off | low | high |
+ * +--------------------------+----------+-----+------+
  */
 enum {
 	KBD_BL_STANDARD      = 1,
@@ -146,6 +169,8 @@ enum {
 	KBD_BL_TRISTATE_AUTO = 3,
 };
 
+#define KBD_BL_AUTO_MODE_HW_BRIGHTNESS	3
+
 #define KBD_BL_QUERY_TYPE		0x1
 #define KBD_BL_TRISTATE_TYPE		0x5
 #define KBD_BL_TRISTATE_AUTO_TYPE	0x7
@@ -204,7 +229,7 @@ struct ideapad_private {
 		bool initialized;
 		int type;
 		struct led_classdev led;
-		unsigned int last_brightness;
+		unsigned int last_hw_brightness;
 		struct mutex mutex; /* protects brightness tracking */
 	} kbd_bl;
 	struct {
@@ -1594,7 +1619,24 @@ static int ideapad_kbd_bl_check_tristate(int type)
 	return (type == KBD_BL_TRISTATE) || (type == KBD_BL_TRISTATE_AUTO);
 }
 
-static int ideapad_kbd_bl_brightness_get(struct ideapad_private *priv)
+static int ideapad_kbd_bl_brightness_parse(struct ideapad_private *priv, unsigned int hw_brightness)
+{
+	/* Off, low or high */
+	if (hw_brightness <= priv->kbd_bl.led.max_brightness)
+		return hw_brightness;
+
+	/* Auto (controlled by EC according to ALS), report as off */
+	if (priv->kbd_bl.type == KBD_BL_TRISTATE_AUTO &&
+	    hw_brightness == KBD_BL_AUTO_MODE_HW_BRIGHTNESS)
+		return 0;
+
+	/* Unknown value */
+	dev_warn(&priv->platform_device->dev,
+		 "Unknown keyboard backlight value: %u", hw_brightness);
+	return -EINVAL;
+}
+
+static int ideapad_kbd_bl_hw_brightness_get(struct ideapad_private *priv)
 {
 	unsigned long value;
 	int err;
@@ -1608,21 +1650,7 @@ static int ideapad_kbd_bl_brightness_get(struct ideapad_private *priv)
 		if (err)
 			return err;
 
-		/* Convert returned value to brightness level */
-		value = FIELD_GET(KBD_BL_GET_BRIGHTNESS, value);
-
-		/* Off, low or high */
-		if (value <= priv->kbd_bl.led.max_brightness)
-			return value;
-
-		/* Auto, report as off */
-		if (value == priv->kbd_bl.led.max_brightness + 1)
-			return 0;
-
-		/* Unknown value */
-		dev_warn(&priv->platform_device->dev,
-			 "Unknown keyboard backlight value: %lu", value);
-		return -EINVAL;
+		return FIELD_GET(KBD_BL_GET_BRIGHTNESS, value);
 	}
 
 	err = eval_hals(priv->adev->handle, &value);
@@ -1632,6 +1660,16 @@ static int ideapad_kbd_bl_brightness_get(struct ideapad_private *priv)
 	return !!test_bit(HALS_KBD_BL_STATE_BIT, &value);
 }
 
+static int ideapad_kbd_bl_brightness_get(struct ideapad_private *priv)
+{
+	int hw_brightness = ideapad_kbd_bl_hw_brightness_get(priv);
+
+	if (hw_brightness < 0)
+		return hw_brightness;
+
+	return ideapad_kbd_bl_brightness_parse(priv, hw_brightness);
+}
+
 static enum led_brightness ideapad_kbd_bl_led_cdev_brightness_get(struct led_classdev *led_cdev)
 {
 	struct ideapad_private *priv = container_of(led_cdev, struct ideapad_private, kbd_bl.led);
@@ -1639,34 +1677,40 @@ static enum led_brightness ideapad_kbd_bl_led_cdev_brightness_get(struct led_cla
 	return ideapad_kbd_bl_brightness_get(priv);
 }
 
-static int ideapad_kbd_bl_brightness_set(struct ideapad_private *priv, unsigned int brightness)
+static int ideapad_kbd_bl_hw_brightness_set(struct ideapad_private *priv,
+					    unsigned int hw_brightness)
 {
-	int err;
 	unsigned long value;
 	int type = priv->kbd_bl.type;
+	int err;
 
 	guard(mutex)(&priv->kbd_bl.mutex);
 
 	if (ideapad_kbd_bl_check_tristate(type)) {
-		if (brightness > priv->kbd_bl.led.max_brightness)
-			return -EINVAL;
-
-		value = FIELD_PREP(KBD_BL_SET_BRIGHTNESS, brightness) |
+		value = FIELD_PREP(KBD_BL_SET_BRIGHTNESS, hw_brightness) |
 			FIELD_PREP(KBD_BL_COMMAND_TYPE, type) |
 			KBD_BL_COMMAND_SET;
 		err = exec_kblc(priv->adev->handle, value);
 	} else {
-		err = exec_sals(priv->adev->handle, brightness ? SALS_KBD_BL_ON : SALS_KBD_BL_OFF);
+		value = hw_brightness ? SALS_KBD_BL_ON : SALS_KBD_BL_OFF;
+		err = exec_sals(priv->adev->handle, value);
 	}
-
 	if (err)
 		return err;
 
-	priv->kbd_bl.last_brightness = brightness;
+	priv->kbd_bl.last_hw_brightness = hw_brightness;
 
 	return 0;
 }
 
+static int ideapad_kbd_bl_brightness_set(struct ideapad_private *priv, unsigned int brightness)
+{
+	if (brightness > priv->kbd_bl.led.max_brightness)
+		return -EINVAL;
+
+	return ideapad_kbd_bl_hw_brightness_set(priv, brightness);
+}
+
 static int ideapad_kbd_bl_led_cdev_brightness_set(struct led_classdev *led_cdev,
 						  enum led_brightness brightness)
 {
@@ -1677,28 +1721,32 @@ static int ideapad_kbd_bl_led_cdev_brightness_set(struct led_classdev *led_cdev,
 
 static void ideapad_kbd_bl_notify(struct ideapad_private *priv)
 {
-	int brightness;
+	int hw_brightness, brightness;
 
 	if (!priv->kbd_bl.initialized)
 		return;
 
 	guard(mutex)(&priv->kbd_bl.mutex);
 
-	brightness = ideapad_kbd_bl_brightness_get(priv);
-	if (brightness < 0)
+	hw_brightness = ideapad_kbd_bl_hw_brightness_get(priv);
+	if (hw_brightness < 0)
 		return;
 
-	if (brightness == priv->kbd_bl.last_brightness)
+	brightness = ideapad_kbd_bl_brightness_parse(priv, hw_brightness);
+	if (brightness < 0)
+		return; /* Reject insane values early. */
+
+	if (priv->kbd_bl.last_hw_brightness == hw_brightness)
 		return;
 
-	priv->kbd_bl.last_brightness = brightness;
+	priv->kbd_bl.last_hw_brightness = hw_brightness;
 
 	led_classdev_notify_brightness_hw_changed(&priv->kbd_bl.led, brightness);
 }
 
 static int ideapad_kbd_bl_init(struct ideapad_private *priv)
 {
-	int brightness, err;
+	int hw_brightness, err;
 
 	if (!priv->features.kbd_bl)
 		return -ENODEV;
@@ -1710,21 +1758,35 @@ static int ideapad_kbd_bl_init(struct ideapad_private *priv)
 	if (err)
 		return err;
 
-	if (ideapad_kbd_bl_check_tristate(priv->kbd_bl.type))
-		priv->kbd_bl.led.max_brightness = 2;
-	else
-		priv->kbd_bl.led.max_brightness = 1;
+	hw_brightness = ideapad_kbd_bl_hw_brightness_get(priv);
+	if (hw_brightness < 0)
+		return hw_brightness;
 
-	brightness = ideapad_kbd_bl_brightness_get(priv);
-	if (brightness < 0)
-		return brightness;
+	priv->kbd_bl.last_hw_brightness = hw_brightness;
 
-	priv->kbd_bl.last_brightness = brightness;
 	priv->kbd_bl.led.name                    = "platform::" LED_FUNCTION_KBD_BACKLIGHT;
 	priv->kbd_bl.led.brightness_get          = ideapad_kbd_bl_led_cdev_brightness_get;
 	priv->kbd_bl.led.brightness_set_blocking = ideapad_kbd_bl_led_cdev_brightness_set;
 	priv->kbd_bl.led.flags                   = LED_BRIGHT_HW_CHANGED | LED_RETAIN_AT_SHUTDOWN;
 
+	switch (priv->kbd_bl.type) {
+	case KBD_BL_TRISTATE_AUTO:
+	case KBD_BL_TRISTATE:
+		priv->kbd_bl.led.max_brightness = 2;
+		break;
+	case KBD_BL_STANDARD:
+		priv->kbd_bl.led.max_brightness = 1;
+		break;
+	default:
+		/* This has already been validated by ideapad_check_features(). */
+		unreachable();
+	}
+
+	/* Reject insane values. */
+	err = ideapad_kbd_bl_brightness_parse(priv, hw_brightness);
+	if (err < 0)
+		return err;
+
 	err = led_classdev_register(&priv->platform_device->dev, &priv->kbd_bl.led);
 	if (err)
 		return err;

-- 
2.55.0

[PATCH v7 13/13] platform/x86: ideapad-laptop: Fully support auto keyboard backlight

[Rong Zhang]

Currently, the auto brightness mode of keyboard backlight maps to
brightness=0 in LED classdev. The only method to switch to such a mode
is by pressing the manufacturer-defined shortcut (Fn+Space). However, 0
is a multiplexed brightness value; writing 0 simply results in the
backlight being turned off.

With brightness processing code decoupled from LED classdev, we can now
fully support the auto brightness mode. In this mode, the keyboard
backlight is controlled by the EC according to the ambient light sensor
(ALS).

To utilize this, a private hardware control trigger "ideapad-auto" is
added, with the event handling procedure calling the
led_trigger_notify_hw_control_changed() interface to activate/deactivate
the private trigger according to the current LED trigger state. To align
with LEDS_BRIGHTNESS_HW_CHANGED, the driver neither depends on
LEDS_TRIGGERS_HW_CHANGED nor selects it.

Meanwhile, block brightness changes on exit to prevent the side effect
of LED device unregistration when the private trigger is active from
resetting the brightness to zero, so that the state of auto mode can
retain among boots.

Acked-by: Ike Panhc <ikepanhc@gmail.com>
Signed-off-by: Rong Zhang <i@rong.moe>
---
Changes in v7:
- Rename the offloaded() callback to hw_offloaded() (thanks Lee Jones)

Changes in v6:
- Simplify the auto mode state preservation logic by converting
  `priv->kbd_bl.initialized' into a tristate integer

Changes in v4:
- Add missing #include (Thanks Ilpo Järvinen)
- Remove needless code alignment (ditto)
- Address concerns from Sashiko
  - Do not notify the LED trigger core when the registration of the
    private trigger has failed
  - https://sashiko.dev/#/patchset/20260719-leds-trigger-hw-changed-v3-0-5fb55722e36e@rong.moe?part=11

Changes in v3:
- Address concerns from Sashiko
  - Fix a race condition in ideapad_kbd_bl_led_cdev_brightness_set()
  - Fix trigger re-registration of ideapad_kbd_bl_auto_trigger
  - https://sashiko.dev/#/patchset/20260618-leds-trigger-hw-changed-v2-0-c28c44053cf3%40rong.moe
- Make registration failures of ideapad_kbd_bl_auto_trigger non-fatal
---
 drivers/platform/x86/lenovo/Kconfig          |   1 +
 drivers/platform/x86/lenovo/ideapad-laptop.c | 119 ++++++++++++++++++++++++---
 2 files changed, 109 insertions(+), 11 deletions(-)

diff --git a/drivers/platform/x86/lenovo/Kconfig b/drivers/platform/x86/lenovo/Kconfig
index 516594993073..a97852b0b228 100644
--- a/drivers/platform/x86/lenovo/Kconfig
+++ b/drivers/platform/x86/lenovo/Kconfig
@@ -16,6 +16,7 @@ config IDEAPAD_LAPTOP
 	select INPUT_SPARSEKMAP
 	select NEW_LEDS
 	select LEDS_CLASS
+	select LEDS_TRIGGERS
 	help
 	  This is a driver for Lenovo IdeaPad netbooks contains drivers for
 	  rfkill switch, hotkey, fan control and backlight control.
diff --git a/drivers/platform/x86/lenovo/ideapad-laptop.c b/drivers/platform/x86/lenovo/ideapad-laptop.c
index b57c4f18d0ea..db03c0c9e497 100644
--- a/drivers/platform/x86/lenovo/ideapad-laptop.c
+++ b/drivers/platform/x86/lenovo/ideapad-laptop.c
@@ -15,6 +15,7 @@
 #include <linux/bug.h>
 #include <linux/cleanup.h>
 #include <linux/compiler.h>
+#include <linux/container_of.h>
 #include <linux/debugfs.h>
 #include <linux/delay.h>
 #include <linux/device.h>
@@ -32,6 +33,7 @@
 #include <linux/platform_device.h>
 #include <linux/platform_profile.h>
 #include <linux/power_supply.h>
+#include <linux/printk.h>
 #include <linux/rfkill.h>
 #include <linux/seq_file.h>
 #include <linux/string_choices.h>
@@ -226,7 +228,10 @@ struct ideapad_private {
 		bool ymc_ec_trigger       : 1;
 	} features;
 	struct {
-		bool initialized;
+		int initialized; /*  0: initializion pending/ongoing/failed
+				  * >0: initializion finished
+				  * <0: unregisteration ongoing/finished
+				  */
 		int type;
 		struct led_classdev led;
 		unsigned int last_hw_brightness;
@@ -1716,14 +1721,68 @@ static int ideapad_kbd_bl_led_cdev_brightness_set(struct led_classdev *led_cdev,
 {
 	struct ideapad_private *priv = container_of(led_cdev, struct ideapad_private, kbd_bl.led);
 
+	/*
+	 * When unregistering: It must be the side effect of LED unregistration
+	 * when our private trigger is active. We've set LED_RETAIN_AT_SHUTDOWN
+	 * to retain led_cdev brightness level. To do the same for auto mode,
+	 * gate changes and return early.
+	 *
+	 * It's needless to gate changes when initializing, as there may be a
+	 * time margin between sysfs attribute creation and state change.
+	 */
+	if (unlikely(priv->kbd_bl.initialized < 0))
+		return 0;
+
 	return ideapad_kbd_bl_brightness_set(priv, brightness);
 }
 
+static int ideapad_kbd_bl_auto_trigger_activate(struct led_classdev *led_cdev)
+{
+	struct ideapad_private *priv = container_of(led_cdev, struct ideapad_private, kbd_bl.led);
+
+	return ideapad_kbd_bl_hw_brightness_set(priv, KBD_BL_AUTO_MODE_HW_BRIGHTNESS);
+}
+
+static bool ideapad_kbd_bl_auto_trigger_hw_offloaded(struct led_classdev *led_cdev)
+{
+	struct ideapad_private *priv = container_of(led_cdev, struct ideapad_private, kbd_bl.led);
+
+	guard(mutex)(&priv->kbd_bl.mutex);
+
+	return priv->kbd_bl.last_hw_brightness == KBD_BL_AUTO_MODE_HW_BRIGHTNESS;
+}
+
+static struct led_hw_trigger_type ideapad_kbd_bl_auto_trigger_type;
+
+static struct led_trigger ideapad_kbd_bl_auto_trigger = {
+	.name = "ideapad-auto",
+	.trigger_type = &ideapad_kbd_bl_auto_trigger_type,
+	.activate = ideapad_kbd_bl_auto_trigger_activate,
+	.hw_offloaded = ideapad_kbd_bl_auto_trigger_hw_offloaded,
+};
+
+static bool ideapad_kbd_bl_auto_trigger_registered;
+
+static void ideapad_kbd_bl_notify_hw_control(struct ideapad_private *priv,
+					     unsigned int hw_brightness)
+{
+	bool hw_control, last_hw_control;
+
+	if (!ideapad_kbd_bl_auto_trigger_registered || priv->kbd_bl.type != KBD_BL_TRISTATE_AUTO)
+		return;
+
+	hw_control = hw_brightness == KBD_BL_AUTO_MODE_HW_BRIGHTNESS;
+	last_hw_control = priv->kbd_bl.last_hw_brightness == KBD_BL_AUTO_MODE_HW_BRIGHTNESS;
+
+	if (hw_control != last_hw_control)
+		led_trigger_notify_hw_control_changed(&priv->kbd_bl.led, hw_control);
+}
+
 static void ideapad_kbd_bl_notify(struct ideapad_private *priv)
 {
 	int hw_brightness, brightness;
 
-	if (!priv->kbd_bl.initialized)
+	if (unlikely(priv->kbd_bl.initialized <= 0))
 		return;
 
 	guard(mutex)(&priv->kbd_bl.mutex);
@@ -1739,6 +1798,8 @@ static void ideapad_kbd_bl_notify(struct ideapad_private *priv)
 	if (priv->kbd_bl.last_hw_brightness == hw_brightness)
 		return;
 
+	ideapad_kbd_bl_notify_hw_control(priv, hw_brightness);
+
 	priv->kbd_bl.last_hw_brightness = hw_brightness;
 
 	led_classdev_notify_brightness_hw_changed(&priv->kbd_bl.led, brightness);
@@ -1751,9 +1812,11 @@ static int ideapad_kbd_bl_init(struct ideapad_private *priv)
 	if (!priv->features.kbd_bl)
 		return -ENODEV;
 
-	if (WARN_ON(priv->kbd_bl.initialized))
+	if (WARN_ON(priv->kbd_bl.initialized > 0))
 		return -EEXIST;
 
+	priv->kbd_bl.initialized = 0;
+
 	err = devm_mutex_init(&priv->platform_device->dev, &priv->kbd_bl.mutex);
 	if (err)
 		return err;
@@ -1771,6 +1834,24 @@ static int ideapad_kbd_bl_init(struct ideapad_private *priv)
 
 	switch (priv->kbd_bl.type) {
 	case KBD_BL_TRISTATE_AUTO:
+		priv->kbd_bl.led.max_brightness = 2;
+
+		if (!ideapad_kbd_bl_auto_trigger_registered) {
+			dev_warn(&priv->platform_device->dev,
+				 "Cannot provide LED trigger %s for keyboard backlight\n",
+				 ideapad_kbd_bl_auto_trigger.name);
+			break;
+		}
+
+		priv->kbd_bl.led.flags |= LED_TRIG_HW_CHANGED;
+		priv->kbd_bl.led.trigger_type = &ideapad_kbd_bl_auto_trigger_type;
+		priv->kbd_bl.led.hw_control_trigger = ideapad_kbd_bl_auto_trigger.name;
+
+		/* Hardware remembers the last brightness level, including auto mode. */
+		if (hw_brightness == KBD_BL_AUTO_MODE_HW_BRIGHTNESS)
+			priv->kbd_bl.led.default_trigger = ideapad_kbd_bl_auto_trigger.name;
+
+		break;
 	case KBD_BL_TRISTATE:
 		priv->kbd_bl.led.max_brightness = 2;
 		break;
@@ -1791,17 +1872,17 @@ static int ideapad_kbd_bl_init(struct ideapad_private *priv)
 	if (err)
 		return err;
 
-	priv->kbd_bl.initialized = true;
+	priv->kbd_bl.initialized = 1;
 
 	return 0;
 }
 
 static void ideapad_kbd_bl_exit(struct ideapad_private *priv)
 {
-	if (!priv->kbd_bl.initialized)
+	if (priv->kbd_bl.initialized <= 0)
 		return;
 
-	priv->kbd_bl.initialized = false;
+	priv->kbd_bl.initialized = -1;
 
 	led_classdev_unregister(&priv->kbd_bl.led);
 }
@@ -2620,17 +2701,30 @@ static int __init ideapad_laptop_init(void)
 {
 	int err;
 
+	err = led_trigger_register(&ideapad_kbd_bl_auto_trigger);
+	if (err) {
+		pr_warn("Failed to register LED trigger %s: %d\n",
+			ideapad_kbd_bl_auto_trigger.name, err);
+	} else {
+		ideapad_kbd_bl_auto_trigger_registered = true;
+	}
+
 	err = ideapad_wmi_driver_register();
 	if (err)
-		return err;
+		goto err_ledtrig;
 
 	err = platform_driver_register(&ideapad_acpi_driver);
-	if (err) {
-		ideapad_wmi_driver_unregister();
-		return err;
-	}
+	if (err)
+		goto err_wmi;
 
 	return 0;
+
+err_wmi:
+	ideapad_wmi_driver_unregister();
+err_ledtrig:
+	if (ideapad_kbd_bl_auto_trigger_registered)
+		led_trigger_unregister(&ideapad_kbd_bl_auto_trigger);
+	return err;
 }
 module_init(ideapad_laptop_init)
 
@@ -2638,6 +2732,9 @@ static void __exit ideapad_laptop_exit(void)
 {
 	platform_driver_unregister(&ideapad_acpi_driver);
 	ideapad_wmi_driver_unregister();
+
+	if (ideapad_kbd_bl_auto_trigger_registered)
+		led_trigger_unregister(&ideapad_kbd_bl_auto_trigger);
 }
 module_exit(ideapad_laptop_exit)
 

-- 
2.55.0

Re: [PATCH v7 02/13] leds: trigger: Move led_trigger_is_hw_controlled() to the right place

[Lee Jones]

--- checkpatch.pl: clean (0 issues) ---

On Mon, 21 Sep 2026, Rong Zhang wrote:

> Currently led_trigger_is_hw_controlled() is placed at led-class.c, which
> is not an right place as it falls into the triggers namespace and does
> triggers stuff.
> 
> Move it into led-triggers.c, and split it into locked and unlocked
> variant for convenience.
> 
> Fixes: b819dc7d8fb2 ("leds: core: Report ENODATA for brightness of hardware controlled LED")
> Acked-by: Ike Panhc <ikepanhc@gmail.com>
> Signed-off-by: Rong Zhang <i@rong.moe>
> ---
> Changes in v3:
> - New patch in the series, the dependency of the following patches
> ---
>  drivers/leds/led-class.c    | 10 ----------
>  drivers/leds/led-triggers.c | 19 +++++++++++++++++++
>  include/linux/leds.h        |  8 ++++++++
>  3 files changed, 27 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> index 4259533dafa1..7110bfbe3b83 100644
> --- a/drivers/leds/led-class.c
> +++ b/drivers/leds/led-class.c
> @@ -27,16 +27,6 @@ static LIST_HEAD(leds_lookup_list);
>  
>  static struct workqueue_struct *leds_wq;
>  
> -static bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
> -{
> -#ifdef CONFIG_LEDS_TRIGGERS
> -	guard(rwsem_read)(&led_cdev->trigger_lock);
> -	return led_cdev->trigger && led_cdev->trigger->trigger_type;
> -#else
> -	return false;
> -#endif
> -}
> -
>  static ssize_t brightness_show(struct device *dev,
>  		struct device_attribute *attr, char *buf)
>  {
> diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
> index b1223218bda1..bf2543538ed0 100644
> --- a/drivers/leds/led-triggers.c
> +++ b/drivers/leds/led-triggers.c
> @@ -7,9 +7,11 @@
>   * Author: Richard Purdie <rpurdie@openedhand.com>
>   */
>  
> +#include <linux/cleanup.h>
>  #include <linux/export.h>
>  #include <linux/kernel.h>
>  #include <linux/list.h>
> +#include <linux/lockdep.h>
>  #include <linux/spinlock.h>
>  #include <linux/device.h>
>  #include <linux/timer.h>
> @@ -33,6 +35,23 @@ trigger_relevant(struct led_classdev *led_cdev, struct led_trigger *trig)
>  	return !trig->trigger_type || trig->trigger_type == led_cdev->trigger_type;
>  }
>  
> +static bool __led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
> +{
> +	lockdep_assert_held(&led_cdev->trigger_lock);
> +
> +	if (!led_cdev->trigger)
> +		return false;
> +
> +	return led_cdev->trigger->trigger_type;

How does this not cause a compiler warning?

This needs to be evaluated properly.

> +}
> +
> +bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
> +{
> +	guard(rwsem_read)(&led_cdev->trigger_lock);
> +	return __led_trigger_is_hw_controlled(led_cdev);
> +}
> +EXPORT_SYMBOL_GPL(led_trigger_is_hw_controlled);
> +
>  ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
>  			  const struct bin_attribute *bin_attr, char *buf,
>  			  loff_t pos, size_t count)
> diff --git a/include/linux/leds.h b/include/linux/leds.h
> index a515f075c29a..46ad2e03e1c6 100644
> --- a/include/linux/leds.h
> +++ b/include/linux/leds.h
> @@ -534,6 +534,8 @@ void led_trigger_set_default(struct led_classdev *led_cdev);
>  int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trigger);
>  void led_trigger_remove(struct led_classdev *led_cdev);
>  
> +bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev);
> +
>  static inline void led_set_trigger_data(struct led_classdev *led_cdev,
>  					void *trigger_data)
>  {
> @@ -584,6 +586,12 @@ static inline int led_trigger_set(struct led_classdev *led_cdev,
>  }
>  
>  static inline void led_trigger_remove(struct led_classdev *led_cdev) {}
> +
> +static inline bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
> +{
> +	return false;
> +}
> +
>  static inline void led_set_trigger_data(struct led_classdev *led_cdev) {}
>  static inline void *led_get_trigger_data(struct led_classdev *led_cdev)
>  {
> 
> -- 
> 2.55.0
> 

-- 
Lee Jones

Re: [PATCH v7 08/13] leds: trigger: netdev: Implement hw_offloaded() callback

[Lee Jones]

--- checkpatch.pl: clean (0 issues) ---

On Mon, 21 Sep 2026, Rong Zhang wrote:

> "netdev" can run in hardware control according to hardware capabilities
> and trigger options.
> 
> Implement hw_offloaded() callback to provide its hardware control state
> to the LED core, and document the relation between the custom
> "offloaded" attribute and the generic "trigger_may_offload_to_hw"
> attribute.
> 
> The callback mimics how the existing "offloaded" attribute does, i.e.,
> locklessly reads hw_control, as it's just a hint and don't need to be
> accurate.
> 
> Acked-by: Ike Panhc <ikepanhc@gmail.com>
> Signed-off-by: Rong Zhang <i@rong.moe>
> ---
> Changes in v7:
> - Rename the offloaded() callback to hw_offloaded() (thanks Lee Jones)
> - Rename the trigger_may_offload attribute to
>   trigger_may_offload_to_hw (ditto)
> 
> Changes in v3:
> - Do not deprecate netdev's "offloaded" attribute (thanks Thomas
>   Weißschuh)
> - Document the relation between the custom "offloaded" attribute and the
>   generic "trigger_may_offload" attribute (ditto)
> ---
>  Documentation/ABI/testing/sysfs-class-led                | 3 +++
>  Documentation/ABI/testing/sysfs-class-led-trigger-netdev | 3 +++
>  drivers/leds/trigger/ledtrig-netdev.c                    | 8 ++++++++
>  3 files changed, 14 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
> index 123e3a15b7d6..ea113fed10ef 100644
> --- a/Documentation/ABI/testing/sysfs-class-led
> +++ b/Documentation/ABI/testing/sysfs-class-led
> @@ -101,6 +101,9 @@ Description:
>  		- `[foo_trigger]`: the trigger is selected and offloaded to
>  		  hardware.
>  
> +		The "netdev" trigger also provides a custom attribute to
> +		indicate its state, see `/sys/class/leds/<led>/offloaded`.
> +
>  What:		/sys/class/leds/<led>/inverted
>  Date:		January 2011
>  KernelVersion:	2.6.38
> diff --git a/Documentation/ABI/testing/sysfs-class-led-trigger-netdev b/Documentation/ABI/testing/sysfs-class-led-trigger-netdev
> index ed46b37ab8a2..203ea58396ed 100644
> --- a/Documentation/ABI/testing/sysfs-class-led-trigger-netdev
> +++ b/Documentation/ABI/testing/sysfs-class-led-trigger-netdev
> @@ -75,6 +75,9 @@ Description:
>  		If 1, the LED blinking in requested mode is offloaded to
>  		hardware.
>  
> +		LED trigger core also provides a generic attribute for this
> +		purpose, see `/sys/class/leds/<led>/trigger_may_offload_to_hw`.
> +
>  What:		/sys/class/leds/<led>/link_10
>  Date:		Jun 2023
>  KernelVersion:	6.5
> diff --git a/drivers/leds/trigger/ledtrig-netdev.c b/drivers/leds/trigger/ledtrig-netdev.c
> index 5b4e92c14dbb..60409f054e22 100644
> --- a/drivers/leds/trigger/ledtrig-netdev.c
> +++ b/drivers/leds/trigger/ledtrig-netdev.c
> @@ -798,10 +798,18 @@ static void netdev_trig_deactivate(struct led_classdev *led_cdev)
>  	kfree(trigger_data);
>  }
>  
> +static bool netdev_trig_hw_offloaded(struct led_classdev *led_cdev)
> +{
> +	struct led_netdev_data *trigger_data = led_get_trigger_data(led_cdev);
> +
> +	return trigger_data->hw_control;

How sure are we that trigger_data can NEVER be NULL?

> +}
> +
>  static struct led_trigger netdev_led_trigger = {
>  	.name = "netdev",
>  	.activate = netdev_trig_activate,
>  	.deactivate = netdev_trig_deactivate,
> +	.hw_offloaded = netdev_trig_hw_offloaded,
>  	.groups = netdev_trig_groups,
>  };
>  
> 
> -- 
> 2.55.0
> 

-- 
Lee Jones

Re: [PATCH v7 02/13] leds: trigger: Move led_trigger_is_hw_controlled() to the right place

[Rong Zhang]

Hi Lee,

Thanks for your review.

On Thu, 2026-09-24 at 09:37 +0100, Lee Jones wrote:
> --- checkpatch.pl: clean (0 issues) ---
> 
> On Mon, 21 Sep 2026, Rong Zhang wrote:
> 
> > Currently led_trigger_is_hw_controlled() is placed at led-class.c, which
> > is not an right place as it falls into the triggers namespace and does
> > triggers stuff.
> > 
> > Move it into led-triggers.c, and split it into locked and unlocked
> > variant for convenience.
> > 
> > Fixes: b819dc7d8fb2 ("leds: core: Report ENODATA for brightness of hardware controlled LED")
> > Acked-by: Ike Panhc <ikepanhc@gmail.com>
> > Signed-off-by: Rong Zhang <i@rong.moe>
> > ---
> > Changes in v3:
> > - New patch in the series, the dependency of the following patches
> > ---
> >  drivers/leds/led-class.c    | 10 ----------
> >  drivers/leds/led-triggers.c | 19 +++++++++++++++++++
> >  include/linux/leds.h        |  8 ++++++++
> >  3 files changed, 27 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c
> > index 4259533dafa1..7110bfbe3b83 100644
> > --- a/drivers/leds/led-class.c
> > +++ b/drivers/leds/led-class.c
> > @@ -27,16 +27,6 @@ static LIST_HEAD(leds_lookup_list);
> >  
> >  static struct workqueue_struct *leds_wq;
> >  
> > -static bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
> > -{
> > -#ifdef CONFIG_LEDS_TRIGGERS
> > -	guard(rwsem_read)(&led_cdev->trigger_lock);
> > -	return led_cdev->trigger && led_cdev->trigger->trigger_type;
> > -#else
> > -	return false;
> > -#endif
> > -}
> > -
> >  static ssize_t brightness_show(struct device *dev,
> >  		struct device_attribute *attr, char *buf)
> >  {
> > diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c
> > index b1223218bda1..bf2543538ed0 100644
> > --- a/drivers/leds/led-triggers.c
> > +++ b/drivers/leds/led-triggers.c
> > @@ -7,9 +7,11 @@
> >   * Author: Richard Purdie <rpurdie@openedhand.com>
> >   */
> >  
> > +#include <linux/cleanup.h>
> >  #include <linux/export.h>
> >  #include <linux/kernel.h>
> >  #include <linux/list.h>
> > +#include <linux/lockdep.h>
> >  #include <linux/spinlock.h>
> >  #include <linux/device.h>
> >  #include <linux/timer.h>
> > @@ -33,6 +35,23 @@ trigger_relevant(struct led_classdev *led_cdev, struct led_trigger *trig)
> >  	return !trig->trigger_type || trig->trigger_type == led_cdev->trigger_type;
> >  }
> >  
> > +static bool __led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
> > +{
> > +	lockdep_assert_held(&led_cdev->trigger_lock);
> > +
> > +	if (!led_cdev->trigger)
> > +		return false;
> > +
> > +	return led_cdev->trigger->trigger_type;
> 
> How does this not cause a compiler warning?

trigger_type is a pointer. Implicitly converting a pointer to boolean via
a return statement is completely valid in C11.

   6.3.1.2 Boolean type
   When any scalar value is converted to _Bool, the result is 0 if the value
   compares equal to 0; otherwise, the result is 1.

   6.8.6.4 The return statement
   ...If the expression has a type different from the return type of the
   function in which it appears, the value is converted as if by
   assignment to an object having the return type of the function.
   
> 
> This needs to be evaluated properly.

If it's preferred to make the intention clearer, how about:

	return led_cdev->trigger->trigger_type != NULL;

Thanks,
Rong

> 
> > +}
> > +
> > +bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
> > +{
> > +	guard(rwsem_read)(&led_cdev->trigger_lock);
> > +	return __led_trigger_is_hw_controlled(led_cdev);
> > +}
> > +EXPORT_SYMBOL_GPL(led_trigger_is_hw_controlled);
> > +
> >  ssize_t led_trigger_write(struct file *filp, struct kobject *kobj,
> >  			  const struct bin_attribute *bin_attr, char *buf,
> >  			  loff_t pos, size_t count)
> > diff --git a/include/linux/leds.h b/include/linux/leds.h
> > index a515f075c29a..46ad2e03e1c6 100644
> > --- a/include/linux/leds.h
> > +++ b/include/linux/leds.h
> > @@ -534,6 +534,8 @@ void led_trigger_set_default(struct led_classdev *led_cdev);
> >  int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trigger);
> >  void led_trigger_remove(struct led_classdev *led_cdev);
> >  
> > +bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev);
> > +
> >  static inline void led_set_trigger_data(struct led_classdev *led_cdev,
> >  					void *trigger_data)
> >  {
> > @@ -584,6 +586,12 @@ static inline int led_trigger_set(struct led_classdev *led_cdev,
> >  }
> >  
> >  static inline void led_trigger_remove(struct led_classdev *led_cdev) {}
> > +
> > +static inline bool led_trigger_is_hw_controlled(struct led_classdev *led_cdev)
> > +{
> > +	return false;
> > +}
> > +
> >  static inline void led_set_trigger_data(struct led_classdev *led_cdev) {}
> >  static inline void *led_get_trigger_data(struct led_classdev *led_cdev)
> >  {
> > 
> > -- 
> > 2.55.0
> > 

Re: [PATCH v7 08/13] leds: trigger: netdev: Implement hw_offloaded() callback

[Rong Zhang]

Hi Lee,

Thanks for your review.

On Thu, 2026-09-24 at 09:53 +0100, Lee Jones wrote:
> --- checkpatch.pl: clean (0 issues) ---
> 
> On Mon, 21 Sep 2026, Rong Zhang wrote:
> 
> > "netdev" can run in hardware control according to hardware capabilities
> > and trigger options.
> > 
> > Implement hw_offloaded() callback to provide its hardware control state
> > to the LED core, and document the relation between the custom
> > "offloaded" attribute and the generic "trigger_may_offload_to_hw"
> > attribute.
> > 
> > The callback mimics how the existing "offloaded" attribute does, i.e.,
> > locklessly reads hw_control, as it's just a hint and don't need to be
> > accurate.
> > 
> > Acked-by: Ike Panhc <ikepanhc@gmail.com>
> > Signed-off-by: Rong Zhang <i@rong.moe>
> > ---
> > Changes in v7:
> > - Rename the offloaded() callback to hw_offloaded() (thanks Lee Jones)
> > - Rename the trigger_may_offload attribute to
> >   trigger_may_offload_to_hw (ditto)
> > 
> > Changes in v3:
> > - Do not deprecate netdev's "offloaded" attribute (thanks Thomas
> >   Weißschuh)
> > - Document the relation between the custom "offloaded" attribute and the
> >   generic "trigger_may_offload" attribute (ditto)
> > ---
> >  Documentation/ABI/testing/sysfs-class-led                | 3 +++
> >  Documentation/ABI/testing/sysfs-class-led-trigger-netdev | 3 +++
> >  drivers/leds/trigger/ledtrig-netdev.c                    | 8 ++++++++
> >  3 files changed, 14 insertions(+)
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
> > index 123e3a15b7d6..ea113fed10ef 100644
> > --- a/Documentation/ABI/testing/sysfs-class-led
> > +++ b/Documentation/ABI/testing/sysfs-class-led
> > @@ -101,6 +101,9 @@ Description:
> >  		- `[foo_trigger]`: the trigger is selected and offloaded to
> >  		  hardware.
> >  
> > +		The "netdev" trigger also provides a custom attribute to
> > +		indicate its state, see `/sys/class/leds/<led>/offloaded`.
> > +
> >  What:		/sys/class/leds/<led>/inverted
> >  Date:		January 2011
> >  KernelVersion:	2.6.38
> > diff --git a/Documentation/ABI/testing/sysfs-class-led-trigger-netdev b/Documentation/ABI/testing/sysfs-class-led-trigger-netdev
> > index ed46b37ab8a2..203ea58396ed 100644
> > --- a/Documentation/ABI/testing/sysfs-class-led-trigger-netdev
> > +++ b/Documentation/ABI/testing/sysfs-class-led-trigger-netdev
> > @@ -75,6 +75,9 @@ Description:
> >  		If 1, the LED blinking in requested mode is offloaded to
> >  		hardware.
> >  
> > +		LED trigger core also provides a generic attribute for this
> > +		purpose, see `/sys/class/leds/<led>/trigger_may_offload_to_hw`.
> > +
> >  What:		/sys/class/leds/<led>/link_10
> >  Date:		Jun 2023
> >  KernelVersion:	6.5
> > diff --git a/drivers/leds/trigger/ledtrig-netdev.c b/drivers/leds/trigger/ledtrig-netdev.c
> > index 5b4e92c14dbb..60409f054e22 100644
> > --- a/drivers/leds/trigger/ledtrig-netdev.c
> > +++ b/drivers/leds/trigger/ledtrig-netdev.c
> > @@ -798,10 +798,18 @@ static void netdev_trig_deactivate(struct led_classdev *led_cdev)
> >  	kfree(trigger_data);
> >  }
> >  
> > +static bool netdev_trig_hw_offloaded(struct led_classdev *led_cdev)
> > +{
> > +	struct led_netdev_data *trigger_data = led_get_trigger_data(led_cdev);
> > +
> > +	return trigger_data->hw_control;
> 
> How sure are we that trigger_data can NEVER be NULL?

The hw_offloaded() callback is protected by led_cdev->trigger_lock, see
__led_trigger_is_hw_controlled().

trigger_data is set in the trigger's activate() callback, which is
protected by led_cdev->trigger_lock.

trigger_data is cleared in led_trigger_set() when removing the current
trigger, which is, again, protected by led_cdev->trigger_lock.

When CONFIG_LEDS_TRIGGERS=n, the code is not built.

If the trigger is currently inactive, the callback cannot be called.

Therefore, it can never be NULL when we reach here.

Note that the trigger's DEVICE_ATTR_RO(offloaded) makes the same
assumption, too.

Thanks,
Rong

> 
> > +}
> > +
> >  static struct led_trigger netdev_led_trigger = {
> >  	.name = "netdev",
> >  	.activate = netdev_trig_activate,
> >  	.deactivate = netdev_trig_deactivate,
> > +	.hw_offloaded = netdev_trig_hw_offloaded,
> >  	.groups = netdev_trig_groups,
> >  };
> >  
> > 
> > -- 
> > 2.55.0
> > 

Re: (subset) [PATCH v7 00/13] leds: Add support for hardware-initiated hardware control trigger transition

[Lee Jones]

On Mon, 21 Sep 2026 03:40:14 +0800, Rong Zhang wrote:
> Some laptops can tune their keyboard backlight according to ambient
> light sensors (auto mode). This capability is essentially a hardware
> control trigger. Meanwhile, such laptops also offer a shrotcut for
> cycling through brightness levels and auto mode. For example, on
> ThinkBook, pressing Fn+Space ("shortcut") cycles keyboard backlight
> levels in the following sequence:
> 
> [...]

Applied, thanks!

[01/13] leds: class: Always protect brightness_show() with led_access
        commit: 6887f40dadb5a263de1d9e4b5517400c08089d35
[02/13] leds: trigger: Move led_trigger_is_hw_controlled() to the right place
        commit: 7879d6277485697cf37eb3c1b89ce260d8c67e4f
[03/13] leds: class: Remove hardware control trigger when writing brightness
        commit: 96b4ddd6d2d8c645d672f1f26130685d9f40cf2f
[04/13] leds: trigger: Move led_trigger_group to the right place
        commit: 43b83e7462e8e9b96e14262c0b6aa739f01c38f7
[05/13] leds: trigger: Add hw_offloaded() callback and provide trigger_may_offload_to_hw attribute
        commit: 8e04e5382aa989ae9a36dc0cb3f3c90347d5607f
[06/13] leds: cros_ec: Implement hw_offloaded() trigger callback
        commit: b366a50d39d13f8230f959b457abcaeba1e7d121
[07/13] leds: turris-omnia: Implement hw_offloaded() trigger callback and declare hw_control_trigger
        commit: f5005c7cec7d4cff58f25442ed6dfca56e42b16d
[08/13] leds: trigger: netdev: Implement hw_offloaded() callback
        commit: 072e0e799bc6b3909afc8fd7fac750b31e37b438
[09/13] leds: trigger: Enforce strict checks in led_trigger_is_hw_controlled()
        commit: 7b9a609575615a3ba18a31a95282e756e34bd506
[10/13] leds: trigger: Add led_trigger_notify_hw_control_changed() interface
        commit: 05b4738b0078f7d6f154f68068a11c8a0635e9df

--
Lee Jones [李琼斯]