linux-kernel - Re: [PATCH 1/2] pwm: make it possible to apply pwm changes in atomic context

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Message-ID: <20231006144456.zybxv2pn4c37fpr3@pengutronix.de>
Date:   Fri, 6 Oct 2023 16:44:56 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-pwm@...r.kernel.org,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Sean Young <sean@...s.org>,
        Daire McNamara <daire.mcnamara@...rochip.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Fabrice Gasnier <fabrice.gasnier@...s.st.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org,
        Fabio Estevam <festevam@...il.com>,
        linux-stm32@...md-mailman.stormreply.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] pwm: make it possible to apply pwm changes in atomic
 context

Hello Thierry,

On Fri, Oct 06, 2023 at 12:27:51PM +0200, Thierry Reding 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/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.
> 
> What about drivers for devices that can be either sleeping or not? There
> are things like regmap which can abstract those differences away, so you
> could have a driver that works on both types of devices, so setting this
> in ops wouldn't be correct all the time. I think can_sleep needs to be
> per-chip rather than per-driver.

I would consider that a theoretic possibility. If there is a hardware
that has a (say) i2c and a memory-mapped register variant, I never
encountered such a thing. Hmm, the dwc driver seems to have a pci and a
memory-mapped variant, both would be "fast" though. (Wouldn't they?)

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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