[PATCH v2 0/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[PATCH v2 0/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[Akinobu Mita]

I sent these patches a long time ago, but I didn't cc them to the DT list,
so the DT bindings changes weren't reviewed.

There have been a lot of changes to pwm-fan since then, and I've updated
the patch, so please review again.

Akinobu Mita (2):
  hwmon: (pwm-fan) add option to leave fan on shutdown
  dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

 Documentation/devicetree/bindings/hwmon/pwm-fan.yaml | 4 ++++
 drivers/hwmon/pwm-fan.c                              | 6 +++++-
 2 files changed, 9 insertions(+), 1 deletion(-)

-- 
2.34.1

[PATCH v2 1/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[Akinobu Mita]

This adds an optional property "retain-state-shutdown" as requested by
Billy Tsai.

Billy said:
 "Our platform is BMC that will use a PWM-FAN driver to control the fan
 on the managed host. In our case, we do not want to stop the fan when
 the BMC is reboot, which may cause the temperature of the managed host
 not to be lowered."

Cc: Jean Delvare <jdelvare@suse.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Rob Herring <robh@kernel.org>
Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
Cc: Conor Dooley <conor+dt@kernel.org>
Cc: Billy Tsai <billy_tsai@aspeedtech.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 drivers/hwmon/pwm-fan.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/hwmon/pwm-fan.c b/drivers/hwmon/pwm-fan.c
index c434db4656e7..dcb48a41f9f0 100644
--- a/drivers/hwmon/pwm-fan.c
+++ b/drivers/hwmon/pwm-fan.c
@@ -51,6 +51,7 @@ struct pwm_fan_ctx {
 	u32 *pulses_per_revolution;
 	ktime_t sample_start;
 	struct timer_list rpm_timer;
+	bool retain_state_shutdown;
 
 	unsigned int pwm_value;
 	unsigned int pwm_fan_state;
@@ -490,6 +491,8 @@ static int pwm_fan_probe(struct platform_device *pdev)
 
 	mutex_init(&ctx->lock);
 
+	ctx->retain_state_shutdown = device_property_read_bool(dev, "retain-state-shutdown");
+
 	ctx->dev = &pdev->dev;
 	ctx->pwm = devm_pwm_get(dev, NULL);
 	if (IS_ERR(ctx->pwm))
@@ -655,7 +658,8 @@ static void pwm_fan_shutdown(struct platform_device *pdev)
 {
 	struct pwm_fan_ctx *ctx = platform_get_drvdata(pdev);
 
-	pwm_fan_cleanup(ctx);
+	if (!ctx->retain_state_shutdown)
+		pwm_fan_cleanup(ctx);
 }
 
 static int pwm_fan_suspend(struct device *dev)
-- 
2.34.1

[PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Akinobu Mita]

Document new retain-state-shutdown property.

Cc: Jean Delvare <jdelvare@suse.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Rob Herring <robh@kernel.org>
Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
Cc: Conor Dooley <conor+dt@kernel.org>
Cc: Billy Tsai <billy_tsai@aspeedtech.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
 Documentation/devicetree/bindings/hwmon/pwm-fan.yaml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
index 4e5abf7580cc..86a069969e29 100644
--- a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
+++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
@@ -40,6 +40,10 @@ properties:
     maximum: 4
     default: 2
 
+  retain-state-shutdown:
+    description: Retain the state of the PWM on shutdown.
+    $ref: /schemas/types.yaml#/definitions/flag
+
   pwms:
     description: The PWM that is used to control the fan.
     maxItems: 1
-- 
2.34.1

Re: [PATCH v2 0/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[Guenter Roeck]

On 10/26/24 01:05, Akinobu Mita wrote:
> I sent these patches a long time ago, but I didn't cc them to the DT list,
> so the DT bindings changes weren't reviewed.
> 
> There have been a lot of changes to pwm-fan since then, and I've updated
> the patch, so please review again.
> 

What changed ? Where is the change log ?

Guenter

> Akinobu Mita (2):
>    hwmon: (pwm-fan) add option to leave fan on shutdown
>    dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property
> 
>   Documentation/devicetree/bindings/hwmon/pwm-fan.yaml | 4 ++++
>   drivers/hwmon/pwm-fan.c                              | 6 +++++-
>   2 files changed, 9 insertions(+), 1 deletion(-)
> 

Re: [PATCH v2 0/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[Akinobu Mita]

2024年10月27日(日) 1:19 Guenter Roeck <linux@roeck-us.net>:
>
> On 10/26/24 01:05, Akinobu Mita wrote:
> > I sent these patches a long time ago, but I didn't cc them to the DT list,
> > so the DT bindings changes weren't reviewed.
> >
> > There have been a lot of changes to pwm-fan since then, and I've updated
> > the patch, so please review again.
> >
>
> What changed ? Where is the change log ?

Sorry, I forgot to write the changelog.

Changes in v2
Patch 1:
- use device_property_read_bool() instead of of_property_read_bool()
- skip calling pwn_fan_cleanup() when newly introduced property is set
  (Since pwm_fan_disable() call in the shutdown() method has been changed to
  pwm_fan_cleanup() call since commit b99152d4f04b ("hwmon: (pwm-fan) Switch
  regulator dynamically"), pwm_fan_disable() no longer exists.)

Patch 2:
- document the new property according to yaml format conversion

Re: [PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Krzysztof Kozlowski]

On Sat, Oct 26, 2024 at 05:05:35PM +0900, Akinobu Mita wrote:
> Document new retain-state-shutdown property.
> 
> Cc: Jean Delvare <jdelvare@suse.com>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
> Cc: Conor Dooley <conor+dt@kernel.org>
> Cc: Billy Tsai <billy_tsai@aspeedtech.com>
> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> ---
>  Documentation/devicetree/bindings/hwmon/pwm-fan.yaml | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> index 4e5abf7580cc..86a069969e29 100644
> --- a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> +++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> @@ -40,6 +40,10 @@ properties:
>      maximum: 4
>      default: 2
>  
> +  retain-state-shutdown:
> +    description: Retain the state of the PWM on shutdown.

You described the desired Linux feature or behavior, not the actual
hardware. The bindings are about the latter, so instead you need to
rephrase the property and its description to match actual hardware
capabilities/features/configuration etc.

Best regards,
Krzysztof

Re: [PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Akinobu Mita]

2024年10月28日(月) 5:38 Krzysztof Kozlowski <krzk@kernel.org>:
>
> On Sat, Oct 26, 2024 at 05:05:35PM +0900, Akinobu Mita wrote:
> > Document new retain-state-shutdown property.
> >
> > Cc: Jean Delvare <jdelvare@suse.com>
> > Cc: Guenter Roeck <linux@roeck-us.net>
> > Cc: Rob Herring <robh@kernel.org>
> > Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
> > Cc: Conor Dooley <conor+dt@kernel.org>
> > Cc: Billy Tsai <billy_tsai@aspeedtech.com>
> > Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> > ---
> >  Documentation/devicetree/bindings/hwmon/pwm-fan.yaml | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> > index 4e5abf7580cc..86a069969e29 100644
> > --- a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> > +++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> > @@ -40,6 +40,10 @@ properties:
> >      maximum: 4
> >      default: 2
> >
> > +  retain-state-shutdown:
> > +    description: Retain the state of the PWM on shutdown.
>
> You described the desired Linux feature or behavior, not the actual
> hardware. The bindings are about the latter, so instead you need to
> rephrase the property and its description to match actual hardware
> capabilities/features/configuration etc.

Is this description okay?
(Reused the description of retain-state-shutdown in leds-gpio.yaml)

description:
  Retain the state of the PWM on shutdown. Useful in BMC systems, for
  example, when the BMC is rebooted while the host remains up, the fan
  will not stop.

Re: [PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Krzysztof Kozlowski]

On 28/10/2024 13:42, Akinobu Mita wrote:
> 2024年10月28日(月) 5:38 Krzysztof Kozlowski <krzk@kernel.org>:
>>
>> On Sat, Oct 26, 2024 at 05:05:35PM +0900, Akinobu Mita wrote:
>>> Document new retain-state-shutdown property.
>>>
>>> Cc: Jean Delvare <jdelvare@suse.com>
>>> Cc: Guenter Roeck <linux@roeck-us.net>
>>> Cc: Rob Herring <robh@kernel.org>
>>> Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
>>> Cc: Conor Dooley <conor+dt@kernel.org>
>>> Cc: Billy Tsai <billy_tsai@aspeedtech.com>
>>> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
>>> ---
>>>  Documentation/devicetree/bindings/hwmon/pwm-fan.yaml | 4 ++++
>>>  1 file changed, 4 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
>>> index 4e5abf7580cc..86a069969e29 100644
>>> --- a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
>>> +++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
>>> @@ -40,6 +40,10 @@ properties:
>>>      maximum: 4
>>>      default: 2
>>>
>>> +  retain-state-shutdown:
>>> +    description: Retain the state of the PWM on shutdown.
>>
>> You described the desired Linux feature or behavior, not the actual
>> hardware. The bindings are about the latter, so instead you need to
>> rephrase the property and its description to match actual hardware
>> capabilities/features/configuration etc.
> 
> Is this description okay?
> (Reused the description of retain-state-shutdown in leds-gpio.yaml)
> 
> description:
>   Retain the state of the PWM on shutdown. Useful in BMC systems, for
>   example, when the BMC is rebooted while the host remains up, the fan
>   will not stop.

Nothing improved in the property. You still say what the system should
do. This is user-space choice, not DT.

Best regards,
Krzysztof

Re: [PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Akinobu Mita]

2024年10月28日(月) 23:22 Krzysztof Kozlowski <krzk@kernel.org>:
>
> On 28/10/2024 13:42, Akinobu Mita wrote:
> > 2024年10月28日(月) 5:38 Krzysztof Kozlowski <krzk@kernel.org>:
> >>
> >> On Sat, Oct 26, 2024 at 05:05:35PM +0900, Akinobu Mita wrote:
> >>> Document new retain-state-shutdown property.
> >>>
> >>> Cc: Jean Delvare <jdelvare@suse.com>
> >>> Cc: Guenter Roeck <linux@roeck-us.net>
> >>> Cc: Rob Herring <robh@kernel.org>
> >>> Cc: Krzysztof Kozlowski <krzk+dt@kernel.org>
> >>> Cc: Conor Dooley <conor+dt@kernel.org>
> >>> Cc: Billy Tsai <billy_tsai@aspeedtech.com>
> >>> Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
> >>> ---
> >>>  Documentation/devicetree/bindings/hwmon/pwm-fan.yaml | 4 ++++
> >>>  1 file changed, 4 insertions(+)
> >>>
> >>> diff --git a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> >>> index 4e5abf7580cc..86a069969e29 100644
> >>> --- a/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> >>> +++ b/Documentation/devicetree/bindings/hwmon/pwm-fan.yaml
> >>> @@ -40,6 +40,10 @@ properties:
> >>>      maximum: 4
> >>>      default: 2
> >>>
> >>> +  retain-state-shutdown:
> >>> +    description: Retain the state of the PWM on shutdown.
> >>
> >> You described the desired Linux feature or behavior, not the actual
> >> hardware. The bindings are about the latter, so instead you need to
> >> rephrase the property and its description to match actual hardware
> >> capabilities/features/configuration etc.
> >
> > Is this description okay?
> > (Reused the description of retain-state-shutdown in leds-gpio.yaml)
> >
> > description:
> >   Retain the state of the PWM on shutdown. Useful in BMC systems, for
> >   example, when the BMC is rebooted while the host remains up, the fan
> >   will not stop.
>
> Nothing improved in the property. You still say what the system should
> do. This is user-space choice, not DT.

It seems better to implement it as a device attribute.

Re: [PATCH v2 1/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[Billy Tsai]

> This adds an optional property "retain-state-shutdown" as requested by
> Billy Tsai.

> Billy said:
>  "Our platform is BMC that will use a PWM-FAN driver to control the fan
>  on the managed host. In our case, we do not want to stop the fan when
>  the BMC is reboot, which may cause the temperature of the managed host
>  not to be lowered."

I confirmed that it works properly.

Reviewed-by: Billy Tsai <billy_tsai@aspeedtech.com>
Tested-by: Billy Tsai <billy_tsai@aspeedtech.com>

Thanks

Re: [PATCH v2 1/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[Akinobu Mita]

2024年10月29日(火) 11:35 Billy Tsai <billy_tsai@aspeedtech.com>:
>
> > This adds an optional property "retain-state-shutdown" as requested by
> > Billy Tsai.
>
> > Billy said:
> >  "Our platform is BMC that will use a PWM-FAN driver to control the fan
> >  on the managed host. In our case, we do not want to stop the fan when
> >  the BMC is reboot, which may cause the temperature of the managed host
> >  not to be lowered."
>
> I confirmed that it works properly.
>
> Reviewed-by: Billy Tsai <billy_tsai@aspeedtech.com>
> Tested-by: Billy Tsai <billy_tsai@aspeedtech.com>

Thank you very much for testing.
However, I plan to change this option to device attribute
(/sys/class/hwmon/hwmonX/retain-state-shutdown) instead of the device tree.

Re: [PATCH v2 1/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[Guenter Roeck]

On 10/30/24 07:55, Akinobu Mita wrote:
> 2024年10月29日(火) 11:35 Billy Tsai <billy_tsai@aspeedtech.com>:
>>
>>> This adds an optional property "retain-state-shutdown" as requested by
>>> Billy Tsai.
>>
>>> Billy said:
>>>   "Our platform is BMC that will use a PWM-FAN driver to control the fan
>>>   on the managed host. In our case, we do not want to stop the fan when
>>>   the BMC is reboot, which may cause the temperature of the managed host
>>>   not to be lowered."
>>
>> I confirmed that it works properly.
>>
>> Reviewed-by: Billy Tsai <billy_tsai@aspeedtech.com>
>> Tested-by: Billy Tsai <billy_tsai@aspeedtech.com>
> 
> Thank you very much for testing.
> However, I plan to change this option to device attribute
> (/sys/class/hwmon/hwmonX/retain-state-shutdown) instead of the device tree.


No, I won't acccept that.

Guenter

Re: [PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Krzysztof Kozlowski]

On 28/10/2024 15:57, Akinobu Mita wrote:
>>>>
>>>> You described the desired Linux feature or behavior, not the actual
>>>> hardware. The bindings are about the latter, so instead you need to
>>>> rephrase the property and its description to match actual hardware
>>>> capabilities/features/configuration etc.
>>>
>>> Is this description okay?
>>> (Reused the description of retain-state-shutdown in leds-gpio.yaml)
>>>
>>> description:
>>>   Retain the state of the PWM on shutdown. Useful in BMC systems, for
>>>   example, when the BMC is rebooted while the host remains up, the fan
>>>   will not stop.
>>
>> Nothing improved in the property. You still say what the system should
>> do. This is user-space choice, not DT.
> 
> It seems better to implement it as a device attribute.

I don't know about that. To repeat: if you say what system is supposed
to be doing, it is a policy. Describe the hardware and its configuration
and maybe this would be suitable for DT.

Best regards,
Krzysztof

Re: [PATCH v2 1/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[Akinobu Mita]

2024年10月31日(木) 0:02 Guenter Roeck <linux@roeck-us.net>:
>
> On 10/30/24 07:55, Akinobu Mita wrote:
> > 2024年10月29日(火) 11:35 Billy Tsai <billy_tsai@aspeedtech.com>:
> >>
> >>> This adds an optional property "retain-state-shutdown" as requested by
> >>> Billy Tsai.
> >>
> >>> Billy said:
> >>>   "Our platform is BMC that will use a PWM-FAN driver to control the fan
> >>>   on the managed host. In our case, we do not want to stop the fan when
> >>>   the BMC is reboot, which may cause the temperature of the managed host
> >>>   not to be lowered."
> >>
> >> I confirmed that it works properly.
> >>
> >> Reviewed-by: Billy Tsai <billy_tsai@aspeedtech.com>
> >> Tested-by: Billy Tsai <billy_tsai@aspeedtech.com>
> >
> > Thank you very much for testing.
> > However, I plan to change this option to device attribute
> > (/sys/class/hwmon/hwmonX/retain-state-shutdown) instead of the device tree.
>
>
> No, I won't acccept that.

Oops, I mean /sys/device/platform/pwm-fan.X/retain-state-shutdown
not /sys/class/hwmon/hwmonX/retain-state-shutdown.

Re: [PATCH v2 1/2] hwmon: (pwm-fan) add option to leave fan on shutdown

[Guenter Roeck]

On 10/30/24 08:18, Akinobu Mita wrote:
> 2024年10月31日(木) 0:02 Guenter Roeck <linux@roeck-us.net>:
>>
>> On 10/30/24 07:55, Akinobu Mita wrote:
>>> 2024年10月29日(火) 11:35 Billy Tsai <billy_tsai@aspeedtech.com>:
>>>>
>>>>> This adds an optional property "retain-state-shutdown" as requested by
>>>>> Billy Tsai.
>>>>
>>>>> Billy said:
>>>>>    "Our platform is BMC that will use a PWM-FAN driver to control the fan
>>>>>    on the managed host. In our case, we do not want to stop the fan when
>>>>>    the BMC is reboot, which may cause the temperature of the managed host
>>>>>    not to be lowered."
>>>>
>>>> I confirmed that it works properly.
>>>>
>>>> Reviewed-by: Billy Tsai <billy_tsai@aspeedtech.com>
>>>> Tested-by: Billy Tsai <billy_tsai@aspeedtech.com>
>>>
>>> Thank you very much for testing.
>>> However, I plan to change this option to device attribute
>>> (/sys/class/hwmon/hwmonX/retain-state-shutdown) instead of the device tree.
>>
>>
>> No, I won't acccept that.
> 
> Oops, I mean /sys/device/platform/pwm-fan.X/retain-state-shutdown
> not /sys/class/hwmon/hwmonX/retain-state-shutdown.

That does not make a difference. It still very much looks like a system property
to me, and making it a device property to be set by userspace just looks like
a workaround to address refusal by dt maintainers to accept the system property.

You'll have to make the case for why this is _not_ a system property for me
to accept it.

Guenter

Re: [PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Akinobu Mita]

2024年10月31日(木) 0:18 Krzysztof Kozlowski <krzk@kernel.org>:
>
> On 28/10/2024 15:57, Akinobu Mita wrote:
> >>>>
> >>>> You described the desired Linux feature or behavior, not the actual
> >>>> hardware. The bindings are about the latter, so instead you need to
> >>>> rephrase the property and its description to match actual hardware
> >>>> capabilities/features/configuration etc.
> >>>
> >>> Is this description okay?
> >>> (Reused the description of retain-state-shutdown in leds-gpio.yaml)
> >>>
> >>> description:
> >>>   Retain the state of the PWM on shutdown. Useful in BMC systems, for
> >>>   example, when the BMC is rebooted while the host remains up, the fan
> >>>   will not stop.
> >>
> >> Nothing improved in the property. You still say what the system should
> >> do. This is user-space choice, not DT.
> >
> > It seems better to implement it as a device attribute.
>
> I don't know about that. To repeat: if you say what system is supposed
> to be doing, it is a policy. Describe the hardware and its configuration
> and maybe this would be suitable for DT.

Billy, could you please write a proper description for this property?
I'm not the right person for this.

Re: [PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Billy Tsai]

> >
> > On 28/10/2024 15:57, Akinobu Mita wrote:
> > >>>>
> > >>>> You described the desired Linux feature or behavior, not the actual
> > >>>> hardware. The bindings are about the latter, so instead you need to
> > >>>> rephrase the property and its description to match actual hardware
> > >>>> capabilities/features/configuration etc.
> > >>>
> > >>> Is this description okay?
> > >>> (Reused the description of retain-state-shutdown in leds-gpio.yaml)
> > >>>
> > >>> description:
> > >>>   Retain the state of the PWM on shutdown. Useful in BMC systems, for
> > >>>   example, when the BMC is rebooted while the host remains up, the fan
> > >>>   will not stop.
> > >>
> > >> Nothing improved in the property. You still say what the system should
> > >> do. This is user-space choice, not DT.
> > >
> > > It seems better to implement it as a device attribute.
> >
> > I don't know about that. To repeat: if you say what system is supposed
> > to be doing, it is a policy. Describe the hardware and its configuration
> > and maybe this would be suitable for DT.

> Billy, could you please write a proper description for this property?
> I'm not the right person for this.

In our hardware, if the system reboots and power remains on the PWM controller
will retain its original settings. However, the pwm-fan.c driver currently disables
the PWM controller during a system reboot. I need this property to prevent pwm-fan.c
from disabling the PWM when the system reboots.
In my point of view, the description can be:
Retain the state of the PWM on shutdown. Some platforms (e.g., BMC) will maintain
the PWM status after the system reboot. Add this property to prevent the PWM from being
disabled during the system reboot.

Thanks

Billy Tsai

Re: [PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Krzysztof Kozlowski]

On 04/11/2024 08:45, Billy Tsai wrote:
>>>
>>> On 28/10/2024 15:57, Akinobu Mita wrote:
>>>>>>>
>>>>>>> You described the desired Linux feature or behavior, not the actual
>>>>>>> hardware. The bindings are about the latter, so instead you need to
>>>>>>> rephrase the property and its description to match actual hardware
>>>>>>> capabilities/features/configuration etc.
>>>>>>
>>>>>> Is this description okay?
>>>>>> (Reused the description of retain-state-shutdown in leds-gpio.yaml)
>>>>>>
>>>>>> description:
>>>>>>   Retain the state of the PWM on shutdown. Useful in BMC systems, for
>>>>>>   example, when the BMC is rebooted while the host remains up, the fan
>>>>>>   will not stop.
>>>>>
>>>>> Nothing improved in the property. You still say what the system should
>>>>> do. This is user-space choice, not DT.
>>>>
>>>> It seems better to implement it as a device attribute.
>>>
>>> I don't know about that. To repeat: if you say what system is supposed
>>> to be doing, it is a policy. Describe the hardware and its configuration
>>> and maybe this would be suitable for DT.
> 
>> Billy, could you please write a proper description for this property?
>> I'm not the right person for this.
> 
> In our hardware, if the system reboots and power remains on the PWM controller
> will retain its original settings. However, the pwm-fan.c driver currently disables
> the PWM controller during a system reboot. I need this property to prevent pwm-fan.c

If we change the PWM core not to disable it, then we have to change
bindings?

How is this binding applicable on system (e.g. on *BSD) which does not
disable PWM on reboot?

> from disabling the PWM when the system reboots.
> In my point of view, the description can be:
> Retain the state of the PWM on shutdown. Some platforms (e.g., BMC) will maintain
> the PWM status after the system reboot. Add this property to prevent the PWM from being
> disabled during the system reboot.

You again describe what OS should do. First and last sentences are the same.

Probably what you want to say is that fan is some critical component
which should not be turned off or left unattended. Or that this hardware
keeps last state of register on reset, so some boards might want to use
it? If the first, then probably different property name. If the second,
current seems fine, just choose some description describing actual hardware.

Best regards,
Krzysztof

Re: [PATCH v2 2/2] dt-bindings: hwmon: pwm-fan: add retain-state-shutdown property

[Billy Tsai]

> >>>
> >>> On 28/10/2024 15:57, Akinobu Mita wrote:
> >>>>>>>
> >>>>>>> You described the desired Linux feature or behavior, not the actual
> >>>>>>> hardware. The bindings are about the latter, so instead you need to
> >>>>>>> rephrase the property and its description to match actual hardware
> >>>>>>> capabilities/features/configuration etc.
> >>>>>>
> >>>>>> Is this description okay?
> >>>>>> (Reused the description of retain-state-shutdown in leds-gpio.yaml)
> >>>>>>
> >>>>>> description:
> >>>>>>   Retain the state of the PWM on shutdown. Useful in BMC systems, for
> >>>>>>   example, when the BMC is rebooted while the host remains up, the fan
> >>>>>>   will not stop.
> >>>>>
> >>>>> Nothing improved in the property. You still say what the system should
> >>>>> do. This is user-space choice, not DT.
> >>>>
> >>>> It seems better to implement it as a device attribute.
> >>>
> >>> I don't know about that. To repeat: if you say what system is supposed
> >>> to be doing, it is a policy. Describe the hardware and its configuration
> >>> and maybe this would be suitable for DT.
> >
> >> Billy, could you please write a proper description for this property?
> >> I'm not the right person for this.
> >
> > In our hardware, if the system reboots and power remains on the PWM controller
> > will retain its original settings. However, the pwm-fan.c driver currently disables
> > the PWM controller during a system reboot. I need this property to prevent pwm-fan.c

> If we change the PWM core not to disable it, then we have to change
> bindings?

If the pwm-fan.c driver doesn't disable the PWM controller, we don't need to add this property.

> How is this binding applicable on system (e.g. on *BSD) which does not
> disable PWM on reboot?

That's why we need this property?

> > from disabling the PWM when the system reboots.
> > In my point of view, the description can be:
> > Retain the state of the PWM on shutdown. Some platforms (e.g., BMC) will maintain
> > the PWM status after the system reboot. Add this property to prevent the PWM from being
> > disabled during the system reboot.

> You again describe what OS should do. First and last sentences are the same.

> Probably what you want to say is that fan is some critical component
> which should not be turned off or left unattended. Or that this hardware
> keeps last state of register on reset, so some boards might want to use
> it? If the first, then probably different property name. If the second,
> current seems fine, just choose some description describing actual hardware.

I think it will be the second one. Is it okay to change the description to the following?
Retain the state of the PWM on shutdown. Some platforms (e.g., BMC) require the PWM to maintain
its last register status on system reboot. Add this property to prevent the PWM from being disabled
during system reboot.

Thanks

Billy Tsai