[PATCH v4 0/2] hwmon: emc2305: Support configurable fan PWM at shutdown

[PATCH v4 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 v4:
- Initialize pwm_shudown array to EMC2305_PWM_SHUTDOWN_UNSET in probe,
  to avoid treating unconfigured channels as valid and written 0
  during shutdown
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                       | 35 +++++++++++++++++++
 2 files changed, 43 insertions(+)

-- 
2.34.1

[PATCH v4 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

[PATCH v4 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 | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/hwmon/emc2305.c b/drivers/hwmon/emc2305.c
index 64b213e1451e..58249b49e264 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 +583,16 @@ 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);
+
+	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;
 }
 
@@ -631,6 +645,9 @@ static int emc2305_probe(struct i2c_client *client)
 	if (ret)
 		return ret;
 
+	for (i = 0; i < EMC2305_PWM_MAX; i++)
+		data->pwm_shutdown[i] = EMC2305_PWM_SHUTDOWN_UNSET;
+
 	pwm_childs = emc2305_probe_childs_from_dt(dev);
 
 	pdata = dev_get_platdata(&client->dev);
@@ -714,6 +731,23 @@ 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 +760,7 @@ 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: [PATCH v4 0/2] hwmon: emc2305: Support configurable fan PWM at shutdown

[Guenter Roeck]

On 3/20/26 08:29, 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.
> 

Sashiko stil finds some problems. Please check.

https://sashiko.dev/#/patchset/20260320152959.1575978-1-florin.leotescu%40oss.nxp.com

Thanks,
Guenter

> Changes in v4:
> - Initialize pwm_shudown array to EMC2305_PWM_SHUTDOWN_UNSET in probe,
>    to avoid treating unconfigured channels as valid and written 0
>    during shutdown
> 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                       | 35 +++++++++++++++++++
>   2 files changed, 43 insertions(+)
> 

Re: [PATCH v4 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property

[Daniel Baluta]

On 3/20/26 17:29, florin.leotescu@oss.nxp.com wrote:
> 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.
AI review suggests to update description to 'Fan speed percent' or 'PWM duty cycle in percent'. This could be an easy update.
More important question here is how should we proceed with the following observation:

"fan-shutdown-percent property is already defined identically in pwm-fan.yaml."

Guenter, should we move it from pwm-fan.yaml to fan-common.yaml and use it here?

Our initial thought was to add have it merged in microchip,emc2305.yaml as it is now

and then factor it out in fan-common.yaml in a later patch.


What do you think?

Re: [PATCH v4 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property

[Guenter Roeck]

On 3/23/26 02:10, Daniel Baluta wrote:
> On 3/20/26 17:29, florin.leotescu@oss.nxp.com wrote:
>> 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.
> AI review suggests to update description to 'Fan speed percent' or 'PWM duty cycle in percent'. This could be an easy update.
> More important question here is how should we proceed with the following observation:
> 
> "fan-shutdown-percent property is already defined identically in pwm-fan.yaml."
> 
> Guenter, should we move it from pwm-fan.yaml to fan-common.yaml and use it here?
> 
> Our initial thought was to add have it merged in microchip,emc2305.yaml as it is now
> 
> and then factor it out in fan-common.yaml in a later patch.
> 
> 
> What do you think?
> 

Both are fine with me, with slight preference for the second approach.
Please do whatever gets approval from DT maintainers.

Thanks,
Guenter

Re: [PATCH v4 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property

[Rob Herring]

On Fri, Mar 20, 2026 at 05:29:58PM +0200, florin.leotescu@oss.nxp.com wrote:
> 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.

Why not a common fan property in fan-common.yaml?

We generally specify fan speeds in RPM (and then map RPMs to duty cycle 
for PWM).

Also, we have (or can have) cooling levels defined. Perhaps we should 
define the cooling level for shutdown? Maybe other things with cooling 
levels need a shutdown level too?

Rob

Re: [PATCH v4 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property

[Guenter Roeck]

On 3/25/26 14:56, Rob Herring wrote:
> On Fri, Mar 20, 2026 at 05:29:58PM +0200, florin.leotescu@oss.nxp.com wrote:
>> 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.
> 
> Why not a common fan property in fan-common.yaml?
> 
> We generally specify fan speeds in RPM (and then map RPMs to duty cycle
> for PWM).
> 

The problem here is mentioning "fan speed" instead of referring to pwm
duty cyle in the first place. It is not just misleading, it is wrong.

It is impossible to associate fan speed with a specific duty cycle because
that differs for each fan. It isn't even consistent for the same fan model -
one never knows what fan speed one gets for a given duty cycle. It depends
on the air flow in the chassis and on fan-to-fan deviations. It will change
over the lifetime of a fan. It may even change with the ambient temperature.
Fan controllers use a feedback loop for that purpose, but that doesn't
work here since, after all, this is a shutdown parameter.

I don't think anything but specifying a shutdown duty cycle is
feasible here.

> Also, we have (or can have) cooling levels defined. Perhaps we should
> define the cooling level for shutdown? Maybe other things with cooling
> levels need a shutdown level too?
> 

Unless I am missing something, the thermal subsystem does not currently have
a concept of a "shutdown cooling state". The driver supports registering
with the thermal subsystem, but it is not mandatory. Even if the thermal
subsystem would support shutdown cooling states or a similar concept,
I do not think it would be a good idea to mandate its existence or in a fan
controller driver.

Thanks,
Guenter