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

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2020年1月9日(木) 1:13 Rob Herring <robh@xxxxxxxxxx>:
>
> On Sun, Dec 22, 2019 at 11:10:22PM +0900, Akinobu Mita wrote:
> > The pwm-fan driver leaves the fun running when shutting down the system.
> > (On the other hand the gpio-fan driver stops it.)
>
> Seemms like we should have consistent behavior independent of what the
> underlying implementation uses. Is there actually a case you'd want to
> leave the fan on? It seems strange to disable in suspend and leave on in
> shutdown.

I agree.  I was trying to keep the current behavior unchanged, so I added
"disable-state-shutdown" property.  But I can't think of any case we want
to leave the fun on in shutdown.

So it's better to change the shutdown behavior and remove the option
completely or add "retain-state-shutdown" property instead.
(The "retain-state-shutdown" property is inspired by gpio-leds)

> Wouldn't the shutdown state depend if the PWM off state is high or low?
> IIRC, i.MX PWM has a quirk that the PWM disabled state is high. Doesn't

It could be possible to affect the shutdown behavior for pwm-fan.
There are three i.MX PWM drivers (pwm-imx1, pwm-imx27, and pwm-tpm).
Do you remember which one actually have such limitation?

Maybe it should be handled by the PWM controller/chip driver and PWM core.
>From the perspective of PWM user drivers for now, we have nothing to do
other than setting duty cycle zero and then disable PWM for stopping the
pwm-fan.

> it also depend on what the PWM driver does in shutdown?

I think so.  But as far as I can see, no PWM drivers implement shutdown
callback.




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