diff options
author | Uwe Kleine-König <u.kleine-koenig@pengutronix.de> | 2021-07-01 10:29:26 +0300 |
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committer | Thierry Reding <thierry.reding@gmail.com> | 2021-11-17 19:09:22 +0300 |
commit | 92f69e582e15bf281ff1ab3ccc7abdd8392550a3 (patch) | |
tree | 763625b54e2b8fe4dde2269972c9754d19e7bfac /drivers/pwm/core.c | |
parent | 77965c98cffe41994dce3389c4aae80e2072f098 (diff) | |
download | linux-92f69e582e15bf281ff1ab3ccc7abdd8392550a3.tar.xz |
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: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Diffstat (limited to 'drivers/pwm/core.c')
-rw-r--r-- | drivers/pwm/core.c | 41 |
1 files changed, 24 insertions, 17 deletions
diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c index c4bbe12cd850..dedf38a81bf9 100644 --- a/drivers/pwm/core.c +++ b/drivers/pwm/core.c @@ -555,26 +555,33 @@ 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) { - err = chip->ops->config(pwm->chip, pwm, - state->duty_cycle, - state->period); - if (err) - return err; + if (!state->enabled) { + if (pwm->state.enabled) + chip->ops->disable(chip, pwm); - pwm->state.period = state->period; - pwm->state.duty_cycle = state->duty_cycle; + return 0; } - 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); - } + /* + * 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); + if (err) + return err; + + pwm->state.period = state->period; + pwm->state.duty_cycle = state->duty_cycle; + + if (!pwm->state.enabled) { + err = chip->ops->enable(chip, pwm); + if (err) + return err; } return 0; |