linux-kernel - Re: [PATCH v2] pwm: Fixes dpm_run_callback() error in pwm_apply

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Date:   Fri, 19 Aug 2022 10:07:48 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Tamseel Shams <m.shams@...sung.com>
Cc:     thierry.reding@...il.com, lee.jones@...aro.org,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        alim.akhtar@...sung.com
Subject: Re: [PATCH v2] pwm: Fixes dpm_run_callback() error in
 pwm_apply_state()

On Fri, Aug 19, 2022 at 10:04:59AM +0530, Tamseel Shams wrote:
> Return invalid argument error from pwm_apply_state()
> call when 'period is not set' or 'duty_cycle is greater
> than period' only when PWM is enabled, so as to fix the
> dpm_run_callback() error seen on exynos SoC during
> Suspend
> 
> There may be situation when PWM is exported using sysfs,
> but at that point period is not set for PWM. At this
> point if we do suspend, then during pwm_apply_state
> function call from pwm_class_suspend, it checks whether
> period is set or not. It is not set now, so it returns
> an invalid argument error which issues dpm_run_callback()
> error
> 
> Suggested-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> Signed-off-by: Tamseel Shams <m.shams@...sung.com>

I still consider this a band aid and I think there is need for prudence
here. Did you verify that all lowlevel drivers handle a state that is
now allowed in a sane way? If you did, you missed at least
pwm-bcm2835.c, I guess there are more but I stopped checking.

So while this change might make sense in the future, I think it's wrong
to do it now.

I stand to the request to find out why pwm->state is strange. Maybe you
just have to fix your .get_state() callback.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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