| Message ID | 20230120120018.161103-3-u.kleine-koenig@pengutronix.de (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | backlight: pwm_bl: Two PWM releated changes | expand |
On Fri, Jan 20, 2023 at 01:00:18PM +0100, Uwe Kleine-König wrote: > Most but not all PWMs drive the PWM pin to its inactive state when > disabled. However if there is no enable_gpio and no regulator the PWM > must drive the inactive state to actually disable the backlight. > > So keep the PWM on in this case. > > Note that to determine if there is a regulator some effort is required > because it might happen that there isn't actually one but the regulator > core gave us a dummy. (A nice side effect is that this makes the > regulator actually optional even on fully constrained systems.) > > This fixes backlight disabling e.g. on i.MX6 when an inverted PWM is > used. > > Hint for the future: If this change results in a regression, the bug is > in the lowlevel PWM driver. :-) > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Thanks for the changes. Looks good: Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org> Daniel.
On Fri, 20 Jan 2023, Uwe Kleine-König wrote: > Most but not all PWMs drive the PWM pin to its inactive state when > disabled. However if there is no enable_gpio and no regulator the PWM > must drive the inactive state to actually disable the backlight. > > So keep the PWM on in this case. > > Note that to determine if there is a regulator some effort is required > because it might happen that there isn't actually one but the regulator > core gave us a dummy. (A nice side effect is that this makes the > regulator actually optional even on fully constrained systems.) > > This fixes backlight disabling e.g. on i.MX6 when an inverted PWM is > used. > > Hint for the future: If this change results in a regression, the bug is > in the lowlevel PWM driver. > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> > --- > drivers/video/backlight/pwm_bl.c | 30 ++++++++++++++++++++++-------- > 1 file changed, 22 insertions(+), 8 deletions(-) Applied, thanks
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 0509fecd5715..fb388148d98f 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -45,9 +45,11 @@ static void pwm_backlight_power_on(struct pwm_bl_data *pb) if (pb->enabled) return; - err = regulator_enable(pb->power_supply); - if (err < 0) - dev_err(pb->dev, "failed to enable power supply\n"); + if (pb->power_supply) { + err = regulator_enable(pb->power_supply); + if (err < 0) + dev_err(pb->dev, "failed to enable power supply\n"); + } if (pb->post_pwm_on_delay) msleep(pb->post_pwm_on_delay); @@ -69,7 +71,8 @@ static void pwm_backlight_power_off(struct pwm_bl_data *pb) if (pb->pwm_off_delay) msleep(pb->pwm_off_delay); - regulator_disable(pb->power_supply); + if (pb->power_supply) + regulator_disable(pb->power_supply); pb->enabled = false; } @@ -109,8 +112,16 @@ static int pwm_backlight_update_status(struct backlight_device *bl) pwm_backlight_power_off(pb); pwm_get_state(pb->pwm, &state); - state.enabled = false; state.duty_cycle = 0; + /* + * We cannot assume a disabled PWM to drive its output to the + * inactive state. If we have an enable GPIO and/or a regulator + * we assume that this isn't relevant and we can disable the PWM + * to save power. If however there is neither an enable GPIO nor + * a regulator keep the PWM on be sure to get a constant + * inactive output. + */ + state.enabled = !pb->power_supply && !pb->enable_gpio; pwm_apply_state(pb->pwm, &state); } @@ -408,7 +419,7 @@ static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb) if (pb->enable_gpio && gpiod_get_value_cansleep(pb->enable_gpio) == 0) active = false; - if (!regulator_is_enabled(pb->power_supply)) + if (pb->power_supply && !regulator_is_enabled(pb->power_supply)) active = false; if (!pwm_is_enabled(pb->pwm)) @@ -489,10 +500,13 @@ static int pwm_backlight_probe(struct platform_device *pdev) goto err_alloc; } - pb->power_supply = devm_regulator_get(&pdev->dev, "power"); + pb->power_supply = devm_regulator_get_optional(&pdev->dev, "power"); if (IS_ERR(pb->power_supply)) { ret = PTR_ERR(pb->power_supply); - goto err_alloc; + if (ret == -ENODEV) + pb->power_supply = NULL; + else + goto err_alloc; } pb->pwm = devm_pwm_get(&pdev->dev, NULL);
Most but not all PWMs drive the PWM pin to its inactive state when disabled. However if there is no enable_gpio and no regulator the PWM must drive the inactive state to actually disable the backlight. So keep the PWM on in this case. Note that to determine if there is a regulator some effort is required because it might happen that there isn't actually one but the regulator core gave us a dummy. (A nice side effect is that this makes the regulator actually optional even on fully constrained systems.) This fixes backlight disabling e.g. on i.MX6 when an inverted PWM is used. Hint for the future: If this change results in a regression, the bug is in the lowlevel PWM driver. Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> --- drivers/video/backlight/pwm_bl.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-)