Re: [PATCH v2 00/11] pwm: Allow .get_state to fail

Andy Shevchenko
2022-12-09T21:48:31Z

On Wed, Nov 30, 2022 at 04:21:37PM +0100, Uwe Kleine-König wrote:
> Hello,
>
> I forgot about this series and was remembered when I talked to Conor
> Dooley about how .get_state() should behave in an error case.
>
> Compared to (implicit) v1, sent with Message-Id: 20220916151506.298488-1-u.kleine-koenig@pengutronix.de
> I changed:
>
> - Patch #1 which does the prototype change now just adds "return 0" to
> all implementations and so gets simpler and doesn't change behaviour.
> The adaptions to the different .get_state() implementations are split
> out into individual patches to ease review.
> - One minor inconsistency fixed in "pwm: Handle .get_state() failures"
> that I noticed while looking into this patch.
> - I skipped changing sun4i.c as I don't know how to handle the error
> there. Someone might want to have a look. (That's not ideal, but it's
> not worse than the same issue before this series.)
>
> In v1 Thierry had the concern:
>
> | That raises the question about what to do in these cases. If we return
> | an error, that could potentially throw off consumers. So perhaps the
> | closest would be to return a disabled PWM? Or perhaps it'd be up to the
> | consumer to provide some fallback configuration for invalidly configured
> | or unconfigured PWMs.
>
> .get_state() is only called in pwm_device_request on a pwm_state that a
> consumer might see. Before my series a consumer might have seen a
> partial modified pwm_state (because .get_state() might have modified
> .period, then stumbled and returned silently). The last patch ensures
> that this partial modification isn't given out to the consumer. Instead
> they now see the same as if .get_state wasn't implemented at all.

I'm wondering why we didn't see a compiler warning about mistyped function
prototypes in some drivers.

P.S. The series is good thing to do, thank you.

--
With Best Regards,
Andy Shevchenko