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Message-ID: <20231004095920.ne7yrrthow6tnuvg@pengutronix.de>
Date: Wed, 4 Oct 2023 11:59:20 +0200
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Sean Young <sean@...s.org>
Cc: Thierry Reding <thierry.reding@...il.com>,
Shawn Guo <shawnguo@...nel.org>,
Sascha Hauer <s.hauer@...gutronix.de>,
Pengutronix Kernel Team <kernel@...gutronix.de>,
Fabio Estevam <festevam@...il.com>,
NXP Linux Team <linux-imx@....com>,
Vladimir Zapolskiy <vz@...ia.com>,
Conor Dooley <conor.dooley@...rochip.com>,
Daire McNamara <daire.mcnamara@...rochip.com>,
Palmer Dabbelt <palmer@...belt.com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Fabrice Gasnier <fabrice.gasnier@...s.st.com>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue <alexandre.torgue@...s.st.com>,
linux-pwm@...r.kernel.org,
Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
linux-stm32@...md-mailman.stormreply.com,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] pwm: make it possible to apply pwm changes in atomic
context
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/ |
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