Hi Hans, On Sat, Oct 21, 2023 at 11:08:22AM +0200, Hans de Goede wrote: > On 10/19/23 12:51, Uwe Kleine-König wrote: > > On Wed, Oct 18, 2023 at 03:57:48PM +0200, Hans de Goede wrote: > >> On 10/17/23 11:17, Sean Young wrote: > >>> Some drivers require sleeping, for example if the pwm device is connected > >>> over i2c. The pwm-ir-tx requires precise timing, and sleeping causes havoc > >>> with the generated IR signal when sleeping occurs. > >>> > >>> This patch makes it possible to use pwm when the driver does not sleep, > >>> by introducing the pwm_can_sleep() function. > >>> > >>> Signed-off-by: Sean Young <sean@xxxxxxxx> > >> > >> I have no objection to this patch by itself, but it seems a bit > >> of unnecessary churn to change all current callers of pwm_apply_state() > >> to a new API. > > > > The idea is to improve the semantic of the function name, see > > https://lore.kernel.org/linux-pwm/20231013180449.mcdmklbsz2rlymzz@xxxxxxxxxxxxxx > > for more context. > > Hmm, so the argument here is that the GPIO API has this, but GPIOs > generally speaking can be set atomically, so there not being able > to set it atomically is special. > > OTOH we have many many many other kernel functions which may sleep > and we don't all postfix them with _can_sleep. > > And for PWM controllers pwm_apply_state is IMHO sorta expected to > sleep. Many of these are attached over I2C so things will sleep, > others have a handshake to wait for the current dutycycle to > end before you can apply a second change on top of an earlier > change during the current dutycycle which often also involves > sleeping. > > So the natural/expeected thing for pwm_apply_state() is to sleep > and thus it does not need a postfix for this IMHO. Most pwm drivers look like they can be made to work in atomic context, I think. Like you say this is not the case for all of them. Whatever we choose to be the default for pwm_apply_state(), we should have a clear function name for the alternative. This is essentially why pam_apply_cansleep() was picked. The alternative to pwm_apply_cansleep() is to have a function name which implies it can be used from atomic context. However, pwm_apply_atomic() is not great because the "atomic" could be confused with the PWM atomic API, not the kernel process/atomic context. So what should the non-sleeping function be called then? - pwm_apply_cannotsleep() - pwm_apply_nosleep() - pwm_apply_nonsleeping() - pwm_apply_atomic_context() > > I think it's very subjective if you consider this > > churn or not. > > I consider it churn because I don't think adding a postfix > for what is the default/expected behavior is a good idea > (with GPIOs not sleeping is the expected behavior). > > I agree that this is very subjective and very much goes > into the territory of bikeshedding. So please consider > the above my 2 cents on this and lets leave it at that. You have a valid point. Let's focus on having descriptive function names. > > While it's nice to have every caller converted in a single > > step, I'd go for > > > > #define pwm_apply_state(pwm, state) pwm_apply_cansleep(pwm, state) > > > > , keep that macro for a while and convert all users step by step. This > > way we don't needlessly break oot code and the changes to convert to the > > new API can go via their usual trees without time pressure. > > I don't think there are enough users of pwm_apply_state() to warrant > such an exercise. > > So if people want to move ahead with the _can_sleep postfix addition > (still not a fan) here is my acked-by for the drivers/platform/x86 > changes, for merging this through the PWM tree in a single commit: > > Acked-by: Hans de Goede <hdegoede@xxxxxxxxxx> Thanks, Sean
