[PATCH v2 0/6] hwmon: (adt7470) Add thermal zone and PWM provider support

[PATCH v2 0/6] hwmon: (adt7470) Add thermal zone and PWM provider support

[Luiz Angelo Daros de Luca]

The ADT7470 is a temperature monitor and PWM fan controller capable of
monitoring up to 10 external temperature sensors and controlling up to 4
PWM outputs.

Currently, the driver exposes these sensors and PWM controls solely via
the standard hwmon sysfs interface. This patch series integrates the
ADT7470 driver with the kernel's thermal and PWM subsystems. This allows
its temperature sensors to be referenced by Device Tree thermal zones,
and its PWM channels to be consumed by generic Device Tree nodes (such
as "pwm-fan").

Patch 1 adds the YAML device tree binding documentation.
Patch 2 and 3 fix two pre-existing bugs found while testing this series
(fans stuck in manual mode after an I2C error, and a
busy-loop/I2C-flooding condition when auto_update_interval or
num_temp_sensors is 0).
Patch 4 performs a minor refactoring to introduce the ADT7470_PWM_MAX
macro.
Patch 5 registers the 4 PWM channels as a generic PWM provider.
Patch 6 registers the external temperature sensors as optional thermal
zones.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>

---
Changes in v2:
- Fixed 2 previous bugs uncovered by Sashiko-bot during review.
- Dropped the thermal cooling device registration for the PWM channels.
- Implemented generic PWM provider support using the PWM subsystem.
- Updated Kconfig to safely handle the PWM subsystem dependency (depends on PWM || PWM=n).
- Updated Device Tree bindings to require #pwm-cells instead of #cooling-cells.
- Link to v1: https://patch.msgid.link/20260716-adt7470_thermalzone-v1-0-cc55ef35edde@gmail.com

To: Guenter Roeck <linux@roeck-us.net>
To: Rob Herring <robh@kernel.org>
To: Krzysztof Kozlowski <krzk+dt@kernel.org>
To: Conor Dooley <conor+dt@kernel.org>
To: de Luca <luizluca@gmail.com>
To: Chris Packham <chris.packham@alliedtelesis.co.nz>
To: Andrew Morton <akpm@linux-foundation.org>
To: "Darrick J. Wong" <djwong@us.ibm.com>
To: Uwe Kleine-König <ukleinek@kernel.org>
Cc: linux-hwmon@vger.kernel.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-pwm@vger.kernel.org

---
Luiz Angelo Daros de Luca (6):
      dt-bindings: hwmon: add binding for adi,adt7470
      hwmon: (adt7470) Fix fans stuck in manual mode on I2C errors
      hwmon: (adt7470) Fix busy-loop and I2C flooding in update thread
      hwmon: (adt7470) Add ADT7470_PWM_MAX macro
      hwmon: (adt7470) Register as a PWM provider
      hwmon: (adt7470) Add thermal zone sensor support

 .../devicetree/bindings/hwmon/adi,adt7470.yaml     |  62 +++++++++++
 drivers/hwmon/Kconfig                              |   1 +
 drivers/hwmon/adt7470.c                            | 118 ++++++++++++++++++---
 3 files changed, 166 insertions(+), 15 deletions(-)
---
base-commit: ca078d004cf58137bcf8cb24a8b271397431ba58
change-id: 20260716-adt7470_thermalzone-59a102278d72

Best regards,
--  
Luiz Angelo Daros de Luca <luizluca@gmail.com>

[PATCH v2 1/6] dt-bindings: hwmon: add binding for adi,adt7470

[Luiz Angelo Daros de Luca]

The Analog Devices ADT7470 is a temperature monitor and PWM fan
controller. It supports up to 10 external temperature sensors and
up to 4 PWM fan outputs.

Add the YAML device tree binding documentation for it. This includes
support for the thermal framework by defining the "#thermal-sensor-cells"
property, and support for the PWM subsystem by defining the "#pwm-cells"
property.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
---
 .../devicetree/bindings/hwmon/adi,adt7470.yaml     | 62 ++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/Documentation/devicetree/bindings/hwmon/adi,adt7470.yaml b/Documentation/devicetree/bindings/hwmon/adi,adt7470.yaml
new file mode 100644
index 000000000000..14bb6359c91f
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/adi,adt7470.yaml
@@ -0,0 +1,62 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/hwmon/adi,adt7470.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Analog Devices ADT7470 hwmon sensor
+
+maintainers:
+  - Luiz Angelo Daros de Luca <luizluca@gmail.com>
+
+description: |
+  The ADT7470 is a temperature monitor and multiple PWM outputs.
+  It supports monitoring up to 10 external temperature sensors and controlling
+  up to four fans.
+
+properties:
+  compatible:
+    const: adi,adt7470
+
+  reg:
+    maxItems: 1
+
+  "#pwm-cells":
+    const: 2
+    description: |
+      Number of cells in a PWM specifier.
+      - The first cell is the PWM channel (0 to 3).
+      - The second cell is the PWM period in nanoseconds.
+
+  "#thermal-sensor-cells":
+    const: 1
+    description: |
+      Number of cells required to uniquely identify the temperature sensors.
+      Valid index values are 0 to 9, corresponding to temp1 through temp10.
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adt7470: hwmon@2f {
+            compatible = "adi,adt7470";
+            reg = <0x2f>;
+            #pwm-cells = <2>;
+            #thermal-sensor-cells = <1>;
+        };
+    };
+
+    fan0 {
+        compatible = "pwm-fan";
+        /* Connects to PWM channel 0 with a 50000 ns (20 kHz) period */
+        pwms = <&adt7470 0 50000>;
+        cooling-levels = <0 100 150 255>;
+    };

-- 
2.55.0

[PATCH v2 2/6] hwmon: (adt7470) Fix fans stuck in manual mode on I2C errors

[Luiz Angelo Daros de Luca]

During adt7470_read_temperatures(), the driver temporarily switches
the PWM channels to manual mode, performs the temperature collection,
and then restores the original configuration registers.

However, if an I2C transaction fails at any point after entering manual
mode, the function aborts and returns immediately. This leaves the
configuration registers un-restored, permanently trapping the fans in
manual mode.

Introduce a recovery path to ensure that the original PWM configuration
registers are always restored, even when intermediate I2C operations
fail.

Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/r/20260716213252.EACA71F000E9@smtp.kernel.org
Fixes: ef67959c4253 ("hwmon: (adt7470) Convert to use regmap")
Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
---
 drivers/hwmon/adt7470.c | 40 +++++++++++++++++++++++++++++-----------
 1 file changed, 29 insertions(+), 11 deletions(-)

diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index 664349756dc2..481d51617f4b 100644
--- a/drivers/hwmon/adt7470.c
+++ b/drivers/hwmon/adt7470.c
@@ -205,11 +205,12 @@ static inline int adt7470_write_word_data(struct adt7470_data *data, unsigned in
 /* Probe for temperature sensors.  Assumes lock is held */
 static int adt7470_read_temperatures(struct adt7470_data *data)
 {
-	unsigned long res;
+	struct device *dev = regmap_get_device(data->regmap);
+	u8 pwm[ADT7470_FAN_COUNT];
 	unsigned int pwm_cfg[2];
-	int err;
+	unsigned long res;
+	int err, err2;
 	int i;
-	u8 pwm[ADT7470_FAN_COUNT];
 
 	/* save pwm[1-4] config register */
 	err = regmap_read(data->regmap, ADT7470_REG_PWM_CFG(0), &pwm_cfg[0]);
@@ -233,19 +234,19 @@ static int adt7470_read_temperatures(struct adt7470_data *data)
 	err = regmap_update_bits(data->regmap, ADT7470_REG_PWM_CFG(2),
 				 ADT7470_PWM_AUTO_MASK, 0);
 	if (err < 0)
-		return err;
+		goto out_restore;
 
 	/* write pwm control to whatever it was */
 	err = regmap_bulk_write(data->regmap, ADT7470_REG_PWM(0), &pwm[0],
 				ADT7470_PWM_COUNT);
 	if (err < 0)
-		return err;
+		goto out_restore;
 
 	/* start reading temperature sensors */
 	err = regmap_update_bits(data->regmap, ADT7470_REG_CFG,
 				 ADT7470_T05_STB_MASK, ADT7470_T05_STB_MASK);
 	if (err < 0)
-		return err;
+		goto out_restore;
 
 	/* Delay is 200ms * number of temp sensors. */
 	res = msleep_interruptible((data->num_temp_sensors >= 0 ?
@@ -256,13 +257,30 @@ static int adt7470_read_temperatures(struct adt7470_data *data)
 	err = regmap_update_bits(data->regmap, ADT7470_REG_CFG,
 				 ADT7470_T05_STB_MASK, 0);
 	if (err < 0)
-		return err;
+		goto out_restore;
 
+out_restore:
 	/* restore pwm[1-4] config registers */
-	err = regmap_write(data->regmap, ADT7470_REG_PWM_CFG(0), pwm_cfg[0]);
-	if (err < 0)
-		return err;
-	err = regmap_write(data->regmap, ADT7470_REG_PWM_CFG(2), pwm_cfg[1]);
+	err2 = regmap_write(data->regmap, ADT7470_REG_PWM_CFG(0), pwm_cfg[0]);
+	if (err2 < 0) {
+		dev_warn_ratelimited(dev,
+				     "failed to restore PWM{1,2} config (%d)\n",
+				     err2);
+
+		if (!err)
+			err = err2;
+	}
+
+	err2 = regmap_write(data->regmap, ADT7470_REG_PWM_CFG(2), pwm_cfg[1]);
+	if (err2 < 0) {
+		dev_warn_ratelimited(dev,
+				     "failed to restore PWM{3,4} config (%d)\n",
+				     err2);
+
+		if (!err)
+			err = err2;
+	}
+
 	if (err < 0)
 		return err;
 

-- 
2.55.0

[PATCH v2 3/6] hwmon: (adt7470) Fix busy-loop and I2C flooding in update thread

[Luiz Angelo Daros de Luca]

When userspace configures 'auto_update_interval' to 0 via sysfs, the
background kthread executes schedule_timeout_interruptible(0), which
returns immediately.

If 'num_temp_sensors' is concurrently or previously set to 0, the
msleep_interruptible() delay inside adt7470_read_temperatures() also
becomes 0. This combination forces the background thread into a tight,
unbounded busy-loop, hogging the CPU and flooding the I2C bus with a
continuous stream of transactions.

Fix this vulnerability by raising the lower limit of the clamp_val in
auto_update_interval_store() from 0 to 500 milliseconds. This guarantees
a reasonable minimum sleep window between sensor updates, protecting the
system from intentional or accidental I2C bus denial of service.

Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/r/20260716213252.EACA71F000E9@smtp.kernel.org
Fixes: 89fac11cb3e7 ("adt7470: make automatic fan control really work")
Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
---
 drivers/hwmon/adt7470.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index 481d51617f4b..77e7be692790 100644
--- a/drivers/hwmon/adt7470.c
+++ b/drivers/hwmon/adt7470.c
@@ -509,7 +509,7 @@ static ssize_t auto_update_interval_store(struct device *dev,
 	if (kstrtol(buf, 10, &temp))
 		return -EINVAL;
 
-	temp = clamp_val(temp, 0, 60000);
+	temp = clamp_val(temp, 500, 60000);
 
 	mutex_lock(&data->lock);
 	data->auto_update_interval = temp;

-- 
2.55.0

[PATCH v2 4/6] hwmon: (adt7470) Add ADT7470_PWM_MAX macro

[Luiz Angelo Daros de Luca]

Instead of a magic 255, use a macro to refer to it.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
---
 drivers/hwmon/adt7470.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index 77e7be692790..d881609c99aa 100644
--- a/drivers/hwmon/adt7470.c
+++ b/drivers/hwmon/adt7470.c
@@ -100,6 +100,7 @@ static const unsigned short normal_i2c[] = { 0x2C, 0x2E, 0x2F, I2C_CLIENT_END };
 #define ADT7470_REG_FAN_MAX(x)	(ADT7470_REG_FAN_MAX_BASE_ADDR + ((x) * 2))
 
 #define ADT7470_PWM_COUNT	4
+#define ADT7470_PWM_MAX		255
 #define ADT7470_REG_PWM(x)	(ADT7470_REG_PWM_BASE_ADDR + (x))
 #define ADT7470_REG_PWM_MAX(x)	(ADT7470_REG_PWM_MAX_BASE_ADDR + (x))
 #define ADT7470_REG_PWM_MIN(x)	(ADT7470_REG_PWM_MIN_BASE_ADDR + (x))
@@ -829,7 +830,7 @@ static int adt7470_pwm_write(struct device *dev, u32 attr, int channel, long val
 
 	switch (attr) {
 	case hwmon_pwm_input:
-		val = clamp_val(val, 0, 255);
+		val = clamp_val(val, 0, ADT7470_PWM_MAX);
 		mutex_lock(&data->lock);
 		data->pwm[channel] = val;
 		err = regmap_write(data->regmap, ADT7470_REG_PWM(channel),
@@ -887,7 +888,7 @@ static ssize_t pwm_max_store(struct device *dev,
 	if (kstrtol(buf, 10, &temp))
 		return -EINVAL;
 
-	temp = clamp_val(temp, 0, 255);
+	temp = clamp_val(temp, 0, ADT7470_PWM_MAX);
 
 	mutex_lock(&data->lock);
 	data->pwm_max[attr->index] = temp;
@@ -922,7 +923,7 @@ static ssize_t pwm_min_store(struct device *dev,
 	if (kstrtol(buf, 10, &temp))
 		return -EINVAL;
 
-	temp = clamp_val(temp, 0, 255);
+	temp = clamp_val(temp, 0, ADT7470_PWM_MAX);
 
 	mutex_lock(&data->lock);
 	data->pwm_min[attr->index] = temp;

-- 
2.55.0

[PATCH v2 5/6] hwmon: (adt7470) Register as a PWM provider

[Luiz Angelo Daros de Luca]

hwmon: (adt7470) Register as a PWM provider

The ADT7470 features four PWM outputs that can be used to control fans.
Previously, these were only accessible through the legacy hwmon sysfs
interface.

Register the ADT7470 as a generic PWM provider. This enables standard
Device Tree PWM consumers, such as "pwm-fan", to use the device through
the "#pwm-cells" property.

When a PWM consumer applies a new PWM state, the driver automatically
switches the corresponding PWM channel to manual mode so that the
requested duty cycle takes effect. The duty cycle specified by the PWM
framework is internally converted to the 0-255 scale expected by the
hardware registers.

The legacy sysfs interface remains unaffected and operates in parallel.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
---
 drivers/hwmon/Kconfig   |  1 +
 drivers/hwmon/adt7470.c | 67 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)

diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 08c29685126a..8838b6714e60 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -224,6 +224,7 @@ config SENSORS_ADT7462
 config SENSORS_ADT7470
 	tristate "Analog Devices ADT7470"
 	depends on I2C
+	depends on PWM || PWM=n
 	select REGMAP_I2C
 	help
 	  If you say yes here you get support for the Analog Devices
diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index d881609c99aa..aaae14a421cd 100644
--- a/drivers/hwmon/adt7470.c
+++ b/drivers/hwmon/adt7470.c
@@ -22,6 +22,7 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/util_macros.h>
+#include <linux/pwm.h>
 
 /* Addresses to scan */
 static const unsigned short normal_i2c[] = { 0x2C, 0x2E, 0x2F, I2C_CLIENT_END };
@@ -864,6 +865,57 @@ static int adt7470_pwm_write(struct device *dev, u32 attr, int channel, long val
 	return err;
 }
 
+static int adt7470_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
+			     const struct pwm_state *state)
+{
+	struct adt7470_data *data = pwmchip_get_drvdata(chip);
+	unsigned int pwm_auto_reg_mask;
+	int err;
+	u8 val;
+
+	if (pwm->hwpwm % 2)
+		pwm_auto_reg_mask = ADT7470_PWM2_AUTO_MASK;
+	else
+		pwm_auto_reg_mask = ADT7470_PWM1_AUTO_MASK;
+
+	if (state->enabled && state->period > 0)
+		val = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * 255, state->period);
+	else
+		val = 0;
+
+	mutex_lock(&data->lock);
+
+	if (data->pwm[pwm->hwpwm] == val &&
+	    data->pwm_automatic[pwm->hwpwm] == 0) {
+		mutex_unlock(&data->lock);
+		return 0;
+	}
+
+	/* Put the PWM channel in manual mode before updating it. */
+	err = regmap_update_bits(data->regmap,
+				 ADT7470_REG_PWM_CFG(pwm->hwpwm),
+				 pwm_auto_reg_mask, 0);
+	if (err < 0)
+		goto out;
+
+	data->pwm_automatic[pwm->hwpwm] = 0;
+
+	err = regmap_write(data->regmap,
+			   ADT7470_REG_PWM(pwm->hwpwm), val);
+	if (err < 0)
+		goto out;
+
+	data->pwm[pwm->hwpwm] = val;
+out:
+	mutex_unlock(&data->lock);
+
+	return err;
+}
+
+static const struct pwm_ops adt7470_pwm_ops = {
+	.apply = adt7470_pwm_apply,
+};
+
 static ssize_t pwm_max_show(struct device *dev,
 			    struct device_attribute *devattr, char *buf)
 {
@@ -1299,6 +1351,21 @@ static int adt7470_probe(struct i2c_client *client)
 	if (IS_ERR(hwmon_dev))
 		return PTR_ERR(hwmon_dev);
 
+	if (IS_REACHABLE(CONFIG_PWM)) {
+		struct pwm_chip *chip;
+
+		chip = devm_pwmchip_alloc(dev, ADT7470_PWM_COUNT, 0);
+		if (IS_ERR(chip))
+			return PTR_ERR(chip);
+
+		chip->ops = &adt7470_pwm_ops;
+		pwmchip_set_drvdata(chip, data);
+
+		err = devm_pwmchip_add(dev, chip);
+		if (err)
+			return dev_warn_probe(dev, err, "failed to register PWM chip\n");
+	}
+
 	data->auto_update = kthread_run(adt7470_update_thread, client, "%s",
 					dev_name(hwmon_dev));
 	if (IS_ERR(data->auto_update))

-- 
2.55.0

[PATCH v2 6/6] hwmon: (adt7470) Add thermal zone sensor support

[Luiz Angelo Daros de Luca]

Expose the ADT7470 external temperature sensors to the thermal
framework using HWMON_C_REGISTER_TZ.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
---
 drivers/hwmon/adt7470.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/hwmon/adt7470.c b/drivers/hwmon/adt7470.c
index aaae14a421cd..595a8f934d60 100644
--- a/drivers/hwmon/adt7470.c
+++ b/drivers/hwmon/adt7470.c
@@ -1251,6 +1251,8 @@ static const struct hwmon_ops adt7470_hwmon_ops = {
 };
 
 static const struct hwmon_channel_info * const adt7470_info[] = {
+	HWMON_CHANNEL_INFO(chip,
+			   HWMON_C_REGISTER_TZ),
 	HWMON_CHANNEL_INFO(temp,
 			   HWMON_T_INPUT | HWMON_T_MIN | HWMON_T_MAX | HWMON_T_ALARM,
 			   HWMON_T_INPUT | HWMON_T_MIN | HWMON_T_MAX | HWMON_T_ALARM,

-- 
2.55.0