Commit 92f69e58 authored by Uwe Kleine-König's avatar Uwe Kleine-König Committed by Thierry Reding
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pwm: Prevent a glitch for legacy drivers 



If a running PWM is reconfigured to disabled calling the ->config()
callback before disabling the hardware might result in a glitch where
the (maybe) new period and duty_cycle are visible on the output before
disabling the hardware.

So handle disabling before calling ->config(). Also exit early in this case
which is possible because period and duty_cycle don't matter for disabled PWMs.
In return however ->config has to be called even if state->period ==
pwm->state.period && state->duty_cycle != pwm->state.duty_cycle because setting
these might have been skipped in the previous call.

Signed-off-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: default avatarThierry Reding <thierry.reding@gmail.com>
parent 77965c98

drivers/pwm/core.c

+24 −17
Original line number Diff line number Diff line
@@ -555,8 +555,20 @@ static int pwm_apply_legacy(struct pwm_chip *chip, struct pwm_device *pwm, 
		pwm->state.polarity = state->polarity;

	}



	if (state->period != pwm->state.period ||

	    state->duty_cycle != pwm->state.duty_cycle) {

	if (!state->enabled) {

		if (pwm->state.enabled)

			chip->ops->disable(chip, pwm);



		return 0;

	}



	/*

	 * We cannot skip calling ->config even if state->period ==

	 * pwm->state.period && state->duty_cycle == pwm->state.duty_cycle

	 * because we might have exited early in the last call to

	 * pwm_apply_state because of !state->enabled and so the two values in

	 * pwm->state might not be configured in hardware.

	 */

	err = chip->ops->config(pwm->chip, pwm,

				state->duty_cycle,

				state->period);
@@ -565,16 +577,11 @@ static int pwm_apply_legacy(struct pwm_chip *chip, struct pwm_device *pwm, 


	pwm->state.period = state->period;

	pwm->state.duty_cycle = state->duty_cycle;

	}



	if (state->enabled != pwm->state.enabled) {

	if (!pwm->state.enabled) {

		err = chip->ops->enable(chip, pwm);

		if (err)

			return err;

		} else {

			chip->ops->disable(chip, pwm);

		}

	}



	return 0;