[RFC PATCH v3 0/2] hwmon: emc2305: Support configurable fan PWM at shutdown

[RFC PATCH v3 0/2] hwmon: emc2305: Support configurable fan PWM at shutdown

[florin.leotescu]

From: Florin Leotescu <florin.leotescu@nxp.com>

This series adds support for configuring the fan PWM duty cycle applied
during system shutdown for the EMC2305 fan controller.

Some platforms require fans to transition to a predefined safe state
during shutdown or reboot handoff until firmware or the next boot stage
reconfigures the controller.

The new optional Device Tree property "fan-shutdown-percent" allows the
shutdown PWM duty cycle to be configured per fan output.

Changes in v3:
- Rebased on current upstream
- Dropped already upstreamed of_node_put(child) fix
Changes in v2:
- Address feedback from Guenter Roeck
- Make shutdown behavior configurable via Device Tree
- Add optional fan-shutdown-percent property
- Apply shutdown PWM only for channels defining the property

Florin Leotescu (2):
  dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property
  hwmon: emc2305: Support configurable fan PWM at shutdown

 .../bindings/hwmon/microchip,emc2305.yaml     |  8 +++++
 drivers/hwmon/emc2305.c                       | 34 +++++++++++++++++++
 2 files changed, 42 insertions(+)

-- 
2.34.1

[RFC PATCH v3 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property

[florin.leotescu]

From: Florin Leotescu <florin.leotescu@nxp.com>

The EMC2305 fan controller supports multiple independent PWM fan
outputs. Some systems require fans to enter a defined safe state
during system shutdown or reboot handoff, until firmware or the next
boot stage reconfigures the controller.

Add an optional "fan-shutdown-percent" property to fan child nodes
allowing the shutdown fan speed to be configured per fan output.

Signed-off-by: Florin Leotescu <florin.leotescu@nxp.com>
---
 .../devicetree/bindings/hwmon/microchip,emc2305.yaml      | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Documentation/devicetree/bindings/hwmon/microchip,emc2305.yaml b/Documentation/devicetree/bindings/hwmon/microchip,emc2305.yaml
index d3f06ebc19fa..7bcadfab9fc4 100644
--- a/Documentation/devicetree/bindings/hwmon/microchip,emc2305.yaml
+++ b/Documentation/devicetree/bindings/hwmon/microchip,emc2305.yaml
@@ -54,6 +54,12 @@ patternProperties:
           The fan number used to determine the associated PWM channel.
         maxItems: 1
 
+      fan-shutdown-percent:
+        description:
+          Fan RPM in percent set during shutdown.
+        minimum: 0
+        maximum: 100
+
     required:
       - reg
 
@@ -80,12 +86,14 @@ examples:
             fan@0 {
                 reg = <0x0>;
                 pwms = <&fan_controller 26000 PWM_POLARITY_INVERTED 1>;
+                fan-shutdown-percent = <100>;
                 #cooling-cells = <2>;
             };
 
             fan@1 {
                 reg = <0x1>;
                 pwms = <&fan_controller 26000 0 1>;
+                fan-shutdown-percent = <50>;
                 #cooling-cells = <2>;
             };
 
-- 
2.34.1

[RFC PATCH v3 2/2] hwmon: emc2305: Support configurable fan PWM at shutdown

[florin.leotescu]

From: Florin Leotescu <florin.leotescu@nxp.com>

Some systems require fans to enter in a defined safe state during system
shutdown or reboot handoff.

Add support for the optional Device Tree property "fan-shutdown-percent"
to configure the shutdown PWM duty cycle per fan output.

If the property is present for a fan channel, the driver converts the
configured percentage value to the corresponding PWM duty cycle and
applies it during driver shutdown.

If the property is not present, the fan state remains unchanged.

Signed-off-by: Florin Leotescu <florin.leotescu@nxp.com>
---
 drivers/hwmon/emc2305.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/hwmon/emc2305.c b/drivers/hwmon/emc2305.c
index 64b213e1451e..e6719cc9dc10 100644
--- a/drivers/hwmon/emc2305.c
+++ b/drivers/hwmon/emc2305.c
@@ -32,6 +32,7 @@
 #define EMC2305_REG_DRIVE_PWM_OUT	0x2b
 #define EMC2305_OPEN_DRAIN		0x0
 #define EMC2305_PUSH_PULL		0x1
+#define EMC2305_PWM_SHUTDOWN_UNSET      -1
 
 #define EMC2305_PWM_DUTY2STATE(duty, max_state, pwm_max) \
 	DIV_ROUND_CLOSEST((duty) * (max_state), (pwm_max))
@@ -104,6 +105,7 @@ struct emc2305_cdev_data {
  * @pwm_output_mask: PWM output mask
  * @pwm_polarity_mask: PWM polarity mask
  * @pwm_separate: separate PWM settings for every channel
+ * @pwm_shutdown: Set shutdown PWM.
  * @pwm_min: array of minimum PWM per channel
  * @pwm_freq: array of PWM frequency per channel
  * @cdev_data: array of cooling devices data
@@ -116,6 +118,7 @@ struct emc2305_data {
 	u8 pwm_output_mask;
 	u8 pwm_polarity_mask;
 	bool pwm_separate;
+	s16 pwm_shutdown[EMC2305_PWM_MAX];
 	u8 pwm_min[EMC2305_PWM_MAX];
 	u16 pwm_freq[EMC2305_PWM_MAX];
 	struct emc2305_cdev_data cdev_data[EMC2305_PWM_MAX];
@@ -539,6 +542,7 @@ static int emc2305_of_parse_pwm_child(struct device *dev,
 				      struct device_node *child,
 				      struct emc2305_data *data)
 {	u32 ch;
+	u32 pwm_shutdown_percent;
 	int ret;
 	struct of_phandle_args args;
 
@@ -579,6 +583,18 @@ static int emc2305_of_parse_pwm_child(struct device *dev,
 	}
 
 	of_node_put(args.np);
+
+	ret = of_property_read_u32(child, "fan-shutdown-percent",
+				   &pwm_shutdown_percent);
+
+	data->pwm_shutdown[ch] = EMC2305_PWM_SHUTDOWN_UNSET;
+
+	if (!ret) {
+		pwm_shutdown_percent = clamp(pwm_shutdown_percent, 0, 100);
+		data->pwm_shutdown[ch] =
+			DIV_ROUND_CLOSEST(pwm_shutdown_percent * EMC2305_FAN_MAX, 100);
+	}
+
 	return 0;
 }
 
@@ -714,6 +730,23 @@ static int emc2305_probe(struct i2c_client *client)
 	return 0;
 }
 
+static void emc2305_shutdown(struct i2c_client *client)
+{
+	int i;
+	int ret;
+	struct emc2305_data *data = i2c_get_clientdata(client);
+
+	for (i = 0; i < data->pwm_num; i++) {
+		if (data->pwm_shutdown[i] != EMC2305_PWM_SHUTDOWN_UNSET) {
+			ret = i2c_smbus_write_byte_data(client, EMC2305_REG_FAN_DRIVE(i),
+							data->pwm_shutdown[i]);
+			if (ret < 0)
+				dev_warn(&client->dev,
+					 "Failed to set shutdown PWM for ch %d\n", i);
+		}
+	}
+}
+
 static const struct of_device_id of_emc2305_match_table[] = {
 	{ .compatible = "microchip,emc2305", },
 	{},
@@ -726,6 +759,7 @@ static struct i2c_driver emc2305_driver = {
 		.of_match_table = of_emc2305_match_table,
 	},
 	.probe = emc2305_probe,
+	.shutdown = emc2305_shutdown,
 	.id_table = emc2305_ids,
 };
 
-- 
2.34.1

Re: [RFC PATCH v3 0/2] hwmon: emc2305: Support configurable fan PWM at shutdown

[Guenter Roeck]

On 3/12/26 07:43, florin.leotescu@oss.nxp.com wrote:
> From: Florin Leotescu <florin.leotescu@nxp.com>
> 
> This series adds support for configuring the fan PWM duty cycle applied
> during system shutdown for the EMC2305 fan controller.
> 
> Some platforms require fans to transition to a predefined safe state
> during shutdown or reboot handoff until firmware or the next boot stage
> reconfigures the controller.
> 
> The new optional Device Tree property "fan-shutdown-percent" allows the
> shutdown PWM duty cycle to be configured per fan output.
> 
> Changes in v3:
> - Rebased on current upstream
> - Dropped already upstreamed of_node_put(child) fix
> Changes in v2:
> - Address feedback from Guenter Roeck
> - Make shutdown behavior configurable via Device Tree
> - Add optional fan-shutdown-percent property
> - Apply shutdown PWM only for channels defining the property
> 
> Florin Leotescu (2):
>    dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property
>    hwmon: emc2305: Support configurable fan PWM at shutdown
> 
>   .../bindings/hwmon/microchip,emc2305.yaml     |  8 +++++
>   drivers/hwmon/emc2305.c                       | 34 +++++++++++++++++++
>   2 files changed, 42 insertions(+)
> 
AI review of series is here:

https://sashiko.dev/#/patchset/20260312144325.1311314-1-florin.leotescu%40oss.nxp.com

Please take a look.

Thanks,
Guenter

Re: [RFC PATCH v3 0/2] hwmon: emc2305: Support configurable fan PWM at shutdown

[Florin Leotescu]

On Tue, Mar 17, 2026 at 09:17:21AM -0700, Guenter Roeck wrote:
> On 3/12/26 07:43, florin.leotescu@oss.nxp.com wrote:
> > From: Florin Leotescu <florin.leotescu@nxp.com>
> > 
> > This series adds support for configuring the fan PWM duty cycle applied
> > during system shutdown for the EMC2305 fan controller.
> > 
> > Some platforms require fans to transition to a predefined safe state
> > during shutdown or reboot handoff until firmware or the next boot stage
> > reconfigures the controller.
> > 
> > The new optional Device Tree property "fan-shutdown-percent" allows the
> > shutdown PWM duty cycle to be configured per fan output.
> > 
> > Changes in v3:
> > - Rebased on current upstream
> > - Dropped already upstreamed of_node_put(child) fix
> > Changes in v2:
> > - Address feedback from Guenter Roeck
> > - Make shutdown behavior configurable via Device Tree
> > - Add optional fan-shutdown-percent property
> > - Apply shutdown PWM only for channels defining the property
> > 
> > Florin Leotescu (2):
> >    dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property
> >    hwmon: emc2305: Support configurable fan PWM at shutdown
> > 
> >   .../bindings/hwmon/microchip,emc2305.yaml     |  8 +++++
> >   drivers/hwmon/emc2305.c                       | 34 +++++++++++++++++++
> >   2 files changed, 42 insertions(+)
> > 
> AI review of series is here:
> 
> https://sashiko.dev/#/patchset/20260312144325.1311314-1-florin.leotescu%40oss.nxp.com
> 
> Please take a look.
>
Hi Guenter,

Thanks for pointing this out.
You're right, since the pwm_shutdown array is zero-initialized by devm_kzalloc,
the channels that are not explicitly configured, will be treated as valid
and written as 0 during shutdown. I'll fix it in next revision.

> Thanks,
> Guenter
>