Re: [PATCH 3/3] pwm: Handle .get_state() failures

[Thierry Reding <thierry.reding@gmail.com>]

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On Fri, Sep 16, 2022 at 05:15:06PM +0200, Uwe Kleine-König wrote:
> This suppresses diagnosis for PWM_DEBUG routines and makes sure that
> pwm->state isn't modified in pwm_device_request() if .get_state() fails.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
> ---
>  drivers/pwm/core.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 381db04cfa00..421573590613 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -108,9 +108,14 @@ static int pwm_device_request(struct pwm_device *pwm, const char *label)
>  	}
>  
>  	if (pwm->chip->ops->get_state) {
> -		err = pwm->chip->ops->get_state(pwm->chip, pwm, &pwm->state);
> +		struct pwm_state state;
> +
> +		err = pwm->chip->ops->get_state(pwm->chip, pwm, &state);
>  		trace_pwm_get(pwm, &pwm->state, err);
>  
> +		if (!err)
> +			pwm->state = state;

So basically this means that callers of pwm_get_state() will get the
zeroed out pwm->state. This can cause issues with the likes of
pwm_set_relative_duty_cycle() which many drivers would use. Do we
perhaps want to set an internal error in this case so that it can be
propagated to callers in pwm_get_state()? That would allow them to fall
back to some default configuration rather than potentially breaking
altogether.

Thierry

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