Messages in this thread | | | Date | Thu, 5 Oct 2023 11:17:13 +0200 | From | Uwe Kleine-König <> | Subject | Re: [PATCH 1/2] pwm: make it possible to apply pwm changes in atomic context |
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Hello Sean,
On Thu, Oct 05, 2023 at 09:30:32AM +0100, Sean Young wrote: > On Wed, Oct 04, 2023 at 11:59:20AM +0200, Uwe Kleine-König wrote: > > On Sun, Oct 01, 2023 at 11:40:29AM +0100, Sean Young wrote: > > > diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c > > > index dc66e3405bf5..d9679ae5b2be 100644 > > > --- a/drivers/pwm/core.c > > > +++ b/drivers/pwm/core.c > > > @@ -505,7 +505,7 @@ int pwm_apply_state(struct pwm_device *pwm, const struct pwm_state *state) > > > * is a bad idea. So make it explicit that calling this function might > > > * sleep. > > > */ > > > - might_sleep(); > > > + might_sleep_if(pwm_can_sleep(pwm)); > > > > > > if (!pwm || !state || !state->period || > > > state->duty_cycle > state->period) > > > > I'd like to have a mechanism to catch drivers that missed to set > > .can_sleep. The best idea I currently have for that is to disable > > preemption if IS_ENABLED(CONFIG_PWM_DEBUG) && !pwm_can_sleep(pwm) while > > .apply() is running. > > If we have pwm_apply_state_atomic(), then CONFIG_DEBUG_ATOMIC_SLEEP will > catch them, but only in that code path of course. > > How about using non_block_start() and non_block_end() if can_sleep is > not set?
TIL, looks like it was created for that task.
> > > diff --git a/drivers/pwm/pwm-fsl-ftm.c b/drivers/pwm/pwm-fsl-ftm.c > > > index b7c6045c5d08..b8b9392844e9 100644 > > > --- a/drivers/pwm/pwm-fsl-ftm.c > > > +++ b/drivers/pwm/pwm-fsl-ftm.c > > > @@ -405,6 +405,7 @@ static int fsl_pwm_probe(struct platform_device *pdev) > > > > > > fpc->soc = of_device_get_match_data(&pdev->dev); > > > fpc->chip.dev = &pdev->dev; > > > + fpc->chip.can_sleep = true; > > > > Also I wonder if the distinction between atomic and sleeping > > pwm_state_apply() should be more explicit. For GPIOs you have a sleeping > > variant gpiod_set_value_cansleep() that allows to immediately determine > > the intended context in the caller. This would allow that programming > > a PWM stays a preemption point (if possible/desired) even if the > > underlying hardware/driver is atomic. To not have to touch all consumer > > drivers, maybe the pair for pwm should better be > > > > pwm_apply_state() > > pwm_apply_state_atomic() > > Do we need pwm_config_atomic(), pwm_enable_atomic(), and pwm_disable_atomic() > too? These are just convenience functions, so we can probably do without them.
I'd like to get rid of these, so for now I'd keep them as is.
> > instead of a "cansleep" suffix for the sleeping variant? Or maybe it's > > better to accept touching all consumer drivers to get semantics similar > > to gpio? I couldn't decide quickly what I really like better here, so > > that's your chance to comment and influence the outcome :-) > > If you expect to have more parameters for pwm_apply_state() then a flags > argument makes sense.
Actually I don't want more parameters -- at least for this use case. I could imagine another parameter for something like apply-immediately vs. complete-current-period, but that's another topic.
> TBH I like the pwm_apply_state_atomic() option.
ok.
Best regards Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ | [unhandled content-type:application/pgp-signature] | |