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Date:   Tue, 12 Dec 2023 12:48:12 +0100
From:   Uwe =?utf-8?Q?Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
To:     Sean Young <sean@mess.org>
Cc:     linux-media@vger.kernel.org, linux-pwm@vger.kernel.org,
        Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Jonathan Corbet <corbet@lwn.net>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v8 4/6] pwm: Make it possible to apply PWM changes in
 atomic context
Message-ID: <20231212114812.afzgjiunzc6druov@pengutronix.de>
References: <cover.1702369869.git.sean@mess.org>
 <57f48330eb606356e86be17f85253f0e3d6ab104.1702369869.git.sean@mess.org>
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Hello Sean,

On Tue, Dec 12, 2023 at 08:34:03AM +0000, Sean Young wrote:
> +/**
> + * pwm_apply_might_sleep() - atomically apply a new state to a PWM device
> + * Cannot be used in atomic context.
> + * @pwm: PWM device
> + * @state: new state to apply
> + */
> +int pwm_apply_might_sleep(struct pwm_device *pwm, const struct pwm_state=
 *state)
> +{
> +	int err;
> +
> +	/*
> +	 * Some lowlevel driver's implementations of .apply() make use of
> +	 * mutexes, also with some drivers only returning when the new
> +	 * configuration is active calling pwm_apply_might_sleep() from atomic =
context
> +	 * is a bad idea. So make it explicit that calling this function might
> +	 * sleep.
> +	 */
> +	might_sleep();
> +
> +	if (IS_ENABLED(CONFIG_PWM_DEBUG) && pwm->chip->atomic) {
> +		/*
> +		 * Catch any drivers that have been marked as atomic but
> +		 * that will sleep anyway.
> +		 */
> +		non_block_start();
> +		err =3D pwm_apply_unchecked(pwm, state);
> +		non_block_end();
> +	} else {
> +		err =3D pwm_apply_unchecked(pwm, state);
> +	}
> +
>  	/*
>  	 * only do this after pwm->state was applied as some
>  	 * implementations of .get_state depend on this
>  	 */
> -	pwm_apply_debug(pwm, state);
> +	if (!err)
> +		pwm_apply_debug(pwm, state);

It's easier to keep that in pwm_apply_unchecked(), isn't it? Then
pwm_apply_atomic() also benefits from the checks.

I'm not so happy with the function name of pwm_apply_unchecked(), but I
don't have a good suggestion either. Probably I'd have chosen
__pam_apply(), but that's probably subjective.

Best regards
Uwe

--=20
Pengutronix e.K.                           | Uwe Kleine-K=F6nig            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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