[PATCH v3 6/7] platform/x86: thinkpad_acpi: Add support for auto keyboard backlight

[Qiling Zhu <kmatzkaczor244@gmail.com>]

Wire the EC keyboard backlight auto mode (level 3) up as a private
hardware control trigger, named "tpacpi-kbd-auto", on top of the LED
hw control trigger framework.  On machines that support auto mode
(MLCG bit 20) the trigger is registered and set as the LED's trigger
type.

Selecting the trigger switches the backlight to auto mode; the
offloaded state is derived from the cached EC level.  When Fn+Space
cycles into or out of auto mode, the driver notifies the trigger core,
so the trigger state shown in the trigger sysfs attribute follows
hardware-initiated transitions.  If the EC is already in auto mode at
driver initialization, the trigger is set as the default one.  Writing
a regular level through either sysfs or proc leaves auto mode, and the
trigger is dropped by the LED core.

Registering the trigger is allowed to fail; basic backlight control
keeps working in that case.

Signed-off-by: Qiling Zhu <kmatzkaczor244@gmail.com>
---
 drivers/platform/x86/lenovo/Kconfig         |  1 +
 drivers/platform/x86/lenovo/thinkpad_acpi.c | 95 +++++++++++++++++++--
 2 files changed, 89 insertions(+), 7 deletions(-)

diff --git a/drivers/platform/x86/lenovo/Kconfig b/drivers/platform/x86/lenovo/Kconfig
index 516594993..77d159a3a 100644
--- a/drivers/platform/x86/lenovo/Kconfig
+++ b/drivers/platform/x86/lenovo/Kconfig
@@ -83,6 +83,7 @@ config THINKPAD_ACPI
 	select NVRAM
 	select NEW_LEDS
 	select LEDS_CLASS
+	select LEDS_TRIGGERS
 	select INPUT_SPARSEKMAP
 	help
 	  This is a driver for the IBM and Lenovo ThinkPad laptops. It adds
diff --git a/drivers/platform/x86/lenovo/thinkpad_acpi.c b/drivers/platform/x86/lenovo/thinkpad_acpi.c
index f9e2d324d..f11e61417 100644
--- a/drivers/platform/x86/lenovo/thinkpad_acpi.c
+++ b/drivers/platform/x86/lenovo/thinkpad_acpi.c
@@ -5106,7 +5106,12 @@ static struct ibm_struct video_driver_data = {
 /* EC level that selects the auto mode for the keyboard backlight */
 #define TPACPI_KBD_LIGHT_AUTO_LEVEL 3
 
-static enum led_brightness kbdlight_brightness;
+/*
+ * Cached EC level, including TPACPI_KBD_LIGHT_AUTO_LEVEL.  All state
+ * tracking compares EC levels; the auto mode is translated to a
+ * brightness value only when reporting to the LED core.
+ */
+static int kbdlight_brightness;
 static DEFINE_MUTEX(kbdlight_mutex);
 
 /*
@@ -5191,6 +5196,38 @@ static bool kbdlight_is_supported(void)
 	return status & BIT(9);
 }
 
+static struct led_hw_trigger_type kbdlight_auto_trigger_type;
+
+static enum led_brightness kbdlight_level_to_brightness(int level)
+{
+	/* Auto mode is not a brightness level; report it as off. */
+	if (level == TPACPI_KBD_LIGHT_AUTO_LEVEL)
+		return 0;
+
+	return level;
+}
+
+static int kbdlight_auto_trigger_activate(struct led_classdev *led_cdev)
+{
+	guard(mutex)(&kbdlight_mutex);
+
+	return kbdlight_set_level(TPACPI_KBD_LIGHT_AUTO_LEVEL);
+}
+
+static bool kbdlight_auto_trigger_hw_offloaded(struct led_classdev *led_cdev)
+{
+	guard(mutex)(&kbdlight_mutex);
+
+	return kbdlight_brightness == TPACPI_KBD_LIGHT_AUTO_LEVEL;
+}
+
+static struct led_trigger kbdlight_auto_trigger = {
+	.name		= "tpacpi-kbd-auto",
+	.trigger_type	= &kbdlight_auto_trigger_type,
+	.activate	= kbdlight_auto_trigger_activate,
+	.hw_offloaded	= kbdlight_auto_trigger_hw_offloaded,
+};
+
 static int kbdlight_set_level_and_update(int level);
 
 static int kbdlight_sysfs_set(struct led_classdev *led_cdev,
@@ -5204,11 +5241,11 @@ static enum led_brightness kbdlight_sysfs_get(struct led_classdev *led_cdev)
 	int level;
 
 	level = kbdlight_get_level();
-	/* Auto mode is not a brightness level; report it as off. */
-	if (level < 0 || level == TPACPI_KBD_LIGHT_AUTO_LEVEL)
+
+	if (level < 0)
 		return 0;
 
-	return level;
+	return kbdlight_level_to_brightness(level);
 }
 
 static struct tpacpi_led_classdev tpacpi_led_kbdlight = {
@@ -5235,9 +5272,37 @@ static int __init kbdlight_init(struct ibm_init_struct *iibm)
 		return -ENODEV;
 	}
 
-	kbdlight_brightness = kbdlight_sysfs_get(NULL);
+	kbdlight_brightness = kbdlight_get_level();
+	if (kbdlight_brightness < 0)
+		kbdlight_brightness = 0;
+
 	tp_features.kbdlight = 1;
 
+	if (tp_features.kbdlight_auto) {
+		rc = devm_led_trigger_register(&tpacpi_pdev->dev,
+					       &kbdlight_auto_trigger);
+		if (rc) {
+			/*
+			 * Auto-mode trigger unavailable; basic backlight
+			 * control keeps working.
+			 */
+			dev_warn(&tpacpi_pdev->dev,
+				 "auto-mode trigger unavailable\n");
+		} else {
+			struct led_classdev *led_cdev =
+				&tpacpi_led_kbdlight.led_classdev;
+
+			led_cdev->flags |= LED_TRIG_HW_CHANGED;
+			led_cdev->trigger_type = &kbdlight_auto_trigger_type;
+			led_cdev->hw_control_trigger =
+				kbdlight_auto_trigger.name;
+
+			if (kbdlight_brightness == TPACPI_KBD_LIGHT_AUTO_LEVEL)
+				led_cdev->default_trigger =
+					kbdlight_auto_trigger.name;
+		}
+	}
+
 	rc = led_classdev_register(&tpacpi_pdev->dev,
 				   &tpacpi_led_kbdlight.led_classdev);
 	if (rc < 0) {
@@ -5347,6 +5412,8 @@ static void kbdlight_resume(void)
 static void kbdlight_notify_level(int level)
 {
 	struct led_classdev *led_cdev = &tpacpi_led_kbdlight.led_classdev;
+	bool is_auto, was_auto;
+	int brightness;
 
 	/*
 	 * Check the brightness actually changed, setting the brightness
@@ -5355,15 +5422,29 @@ static void kbdlight_notify_level(int level)
 	if (level == kbdlight_brightness)
 		return;
 
+	is_auto = level == TPACPI_KBD_LIGHT_AUTO_LEVEL;
+	was_auto = kbdlight_brightness == TPACPI_KBD_LIGHT_AUTO_LEVEL;
+
+	if (is_auto != was_auto)
+		led_trigger_notify_hw_control_changed(led_cdev, is_auto);
+
 	kbdlight_brightness = level;
-	led_classdev_notify_brightness_hw_changed(led_cdev, level);
+	brightness = kbdlight_level_to_brightness(level);
+
+	led_classdev_notify_brightness_hw_changed(led_cdev, brightness);
 }
 
 static void kbdlight_notify_change(void)
 {
+	int level;
+
 	guard(mutex)(&kbdlight_mutex);
 
-	kbdlight_notify_level(kbdlight_sysfs_get(NULL));
+	level = kbdlight_get_level();
+	if (level < 0)
+		return;
+
+	kbdlight_notify_level(level);
 }
 
 static struct ibm_struct kbdlight_driver_data = {
-- 
2.56.1