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[RFC PATCH v2 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property

florin.leotescu@oss.nxp.com posted 2 patches 3 weeks, 5 days ago
There is a newer version of this series
[RFC PATCH v2 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property
Posted by florin.leotescu@oss.nxp.com 3 weeks, 5 days ago 
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
Re: [RFC PATCH v2 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property
Posted by Conor Dooley 3 weeks, 4 days ago 
On Thu, Mar 12, 2026 at 02:22:47PM +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.
> 
> 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.

This sounds like something generic, that other devices might need and
should be in fan-common.yaml?

> +        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
>
Re: [RFC PATCH v2 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property
Posted by Florin Leotescu 3 weeks, 3 days ago 
On Thu, Mar 12, 2026 at 05:37:51PM +0000, Conor Dooley wrote:
> On Thu, Mar 12, 2026 at 02:22:47PM +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.
> > 
> > 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.
> 
> This sounds like something generic, that other devices might need and
> should be in fan-common.yaml?
>
Thanks for the feedback.

The property name was reused from pwm-fan.yaml where it already exists
with the same meaning. I kept it local to minimize the scope of the change.

However, if you prefer it to be modelled as a common property, I can adjust it in the next revision.

> > +        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
> >
Re: [RFC PATCH v2 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property
Posted by Conor Dooley 3 weeks, 3 days ago 
On Fri, Mar 13, 2026 at 07:14:33PM +0200, Florin Leotescu wrote:
> On Thu, Mar 12, 2026 at 05:37:51PM +0000, Conor Dooley wrote:
> > On Thu, Mar 12, 2026 at 02:22:47PM +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.
> > > 
> > > 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.
> > 
> > This sounds like something generic, that other devices might need and
> > should be in fan-common.yaml?
> >
> Thanks for the feedback.
> 
> The property name was reused from pwm-fan.yaml where it already exists
> with the same meaning. I kept it local to minimize the scope of the change.
> 
> However, if you prefer it to be modelled as a common property, I can adjust it in the next revision.

I see. Makes me wonder why half the properties in pwm-fan aren't also in
fan-common.

I suppose there's a reason for it, carry on I guess.. Can be lifted if
there are more users other than you and pwm-fan.

> > > +        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>;

Also leads to the question of why these devices aren't pwm-fans. Too
late now to change anything, I just wanna understand why.

> > >                  #cooling-cells = <2>;
> > >              };
> > >  
> > >              fan@1 {
> > >                  reg = <0x1>;
> > >                  pwms = <&fan_controller 26000 0 1>;
> > > +                fan-shutdown-percent = <50>;
> > >                  #cooling-cells = <2>;
> > >              };
> > >  
> > > -- 
> > > 2.34.1
> > > 
> 
>
Re: [RFC PATCH v2 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property
Posted by Guenter Roeck 3 weeks, 3 days ago 
On 3/13/26 10:38, Conor Dooley wrote:
> On Fri, Mar 13, 2026 at 07:14:33PM +0200, Florin Leotescu wrote:
>> On Thu, Mar 12, 2026 at 05:37:51PM +0000, Conor Dooley wrote:
>>> On Thu, Mar 12, 2026 at 02:22:47PM +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.
>>>>
>>>> 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.
>>>
>>> This sounds like something generic, that other devices might need and
>>> should be in fan-common.yaml?
>>>
>> Thanks for the feedback.
>>
>> The property name was reused from pwm-fan.yaml where it already exists
>> with the same meaning. I kept it local to minimize the scope of the change.
>>
>> However, if you prefer it to be modelled as a common property, I can adjust it in the next revision.
> 
> I see. Makes me wonder why half the properties in pwm-fan aren't also in
> fan-common.
> 
> I suppose there's a reason for it, carry on I guess.. Can be lifted if
> there are more users other than you and pwm-fan.
> 
>>>> +        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>;
> 
> Also leads to the question of why these devices aren't pwm-fans. Too
> late now to change anything, I just wanna understand why.
> 

They are dedicated fan controllers, with an internal tach -> pwm feedback
loop. I don't mind modeling them as pwm controllers if there is a use case
(such as someone using a PWM output to control a LED), but I don't even know
how modeling them as pwm fans using the pwm-fan compatible would even be
possible since that would exclude the tach -> pwm feedback loop.

Also, if that were to be done, we might end up with two hwmon drivers
for one chip: one to report the fan speed, and one to report pwm values.
On top of that, even if it is not currently supported by the driver,
controlling the tach -> pwm feedback loop would become awkward.

Yes, I understand, there is a strong push to model everything with
a pwm output as pwm controller, but si far no one was able to describe
to me how to model a fan controller, and especially its feedback loop,
in such a scenario. That becomes even more complicated if temperatures
are used to control the feedback loop.

Guenter

>>>>                   #cooling-cells = <2>;
>>>>               };
>>>>   
>>>>               fan@1 {
>>>>                   reg = <0x1>;
>>>>                   pwms = <&fan_controller 26000 0 1>;
>>>> +                fan-shutdown-percent = <50>;
>>>>                   #cooling-cells = <2>;
>>>>               };
>>>>   
>>>> -- 
>>>> 2.34.1
>>>>
>>
>>
Re: [RFC PATCH v2 1/2] dt-bindings: hwmon: emc2305: Add fan-shutdown-percent property
Posted by Conor Dooley 3 weeks, 3 days ago 
On Fri, Mar 13, 2026 at 11:12:26AM -0700, Guenter Roeck wrote:
> On 3/13/26 10:38, Conor Dooley wrote:
> > On Fri, Mar 13, 2026 at 07:14:33PM +0200, Florin Leotescu wrote:
> > > On Thu, Mar 12, 2026 at 05:37:51PM +0000, Conor Dooley wrote:
> > > > On Thu, Mar 12, 2026 at 02:22:47PM +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.
> > > > > 
> > > > > 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.
> > > > 
> > > > This sounds like something generic, that other devices might need and
> > > > should be in fan-common.yaml?
> > > > 
> > > Thanks for the feedback.
> > > 
> > > The property name was reused from pwm-fan.yaml where it already exists
> > > with the same meaning. I kept it local to minimize the scope of the change.
> > > 
> > > However, if you prefer it to be modelled as a common property, I can adjust it in the next revision.
> > 
> > I see. Makes me wonder why half the properties in pwm-fan aren't also in
> > fan-common.
> > 
> > I suppose there's a reason for it, carry on I guess.. Can be lifted if
> > there are more users other than you and pwm-fan.
> > 
> > > > > +        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>;
> > 
> > Also leads to the question of why these devices aren't pwm-fans. Too
> > late now to change anything, I just wanna understand why.
> > 
> 
> They are dedicated fan controllers, with an internal tach -> pwm feedback
> loop. I don't mind modeling them as pwm controllers if there is a use case
> (such as someone using a PWM output to control a LED), but I don't even know
> how modeling them as pwm fans using the pwm-fan compatible would even be
> possible since that would exclude the tach -> pwm feedback loop.
> 
> Also, if that were to be done, we might end up with two hwmon drivers
> for one chip: one to report the fan speed, and one to report pwm values.
> On top of that, even if it is not currently supported by the driver,
> controlling the tach -> pwm feedback loop would become awkward.
> 
> Yes, I understand, there is a strong push to model everything with
> a pwm output as pwm controller, but si far no one was able to describe
> to me how to model a fan controller, and especially its feedback loop,
> in such a scenario. That becomes even more complicated if temperatures
> are used to control the feedback loop.

FWIW, my wording choice was poor here. I said that it was too late to
change anything in an attempt to convey that I didn't want it to be
changed, but it came across as implying that it was wrong.
I just wanted to know why it was the way it was, not change it.

Thanks for the info you provided, that's useful.

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