linux-kernel - Re: [PATCH v6 6/7] pwm: pca9685: Restrict period change for prescaler users

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Date:   Mon, 29 Mar 2021 19:15:59 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     linux-pwm@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Sven Van Asbroeck <TheSven73@...il.com>,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: Re: [PATCH v6 6/7] pwm: pca9685: Restrict period change for
 prescaler users

On Mon, Mar 29, 2021 at 02:57:06PM +0200, Clemens Gruber wrote:
> @@ -330,14 +345,22 @@ static int pca9685_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
>  
>  	if (!state->enabled || duty < 1) {
>  		pca9685_pwm_set_duty(pca, pwm->hwpwm, 0);
> +		clear_bit(pwm->hwpwm, pca->prescaler_users);

Hmm, so if "my" channel runs at say

	.duty_cycle = 2539520 ns
	.period = 5079040 ns

and I call pwm_apply_state(mypwm, { .duty_cycle = 0, .period = 5079040,
enabled = true }); it might happen that another channel modifies the
period and I won't be able to return to the initial setting.

So I think it's sensible to only clear the user bit if the PWM is
disabled, but not if it is configured for duty_cycle = 0.

Does this make sense?

Best regards
Uwe

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

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