Messages in this thread | | | Date | Wed, 4 Oct 2023 11:59:20 +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 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.
> 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;
As .apply() being callable in non-sleepable context only depends on .apply() I think a better place for this property is in struct pwm_ops.
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()
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 :-)
Best regards Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ | [unhandled content-type:application/pgp-signature] | |