On Wed, Oct 18, 2023 at 11:07:41PM +0200, Uwe Kleine-König wrote: > Hello Philipp, > > On Thu, Jun 08, 2023 at 04:11:14PM +0200, Philipp Zabel wrote: > > The initial PWM state returned by pwm_init_state() has a duty cycle > > of 0 ns. > > This is only true for drivers without a .get_state() callback, isn't it? pwm_init_state() explicitly zeros the duty-cycle in order to avoid problems when the default args have a different period to the currently applied config: https://elixir.bootlin.com/linux/latest/source/include/linux/pwm.h#L174 Daniel. > > To avoid backlight flicker when taking over an enabled > > display from the bootloader, skip the initial pwm_apply_state() > > and leave the PWM be until backlight_update_state() will apply the > > state with the desired brightness. > > > > Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> > > --- > > With a PWM driver that allows to inherit PWM state from the bootloader, > > postponing the initial pwm_apply_state() with 0 ns duty cycle allows to > > set the desired duty cycle before the PWM is set, avoiding a short flicker > > if the backlight was previously enabled and will be enabled again. > > --- > > drivers/video/backlight/pwm_bl.c | 16 ++++++++-------- > > 1 file changed, 8 insertions(+), 8 deletions(-) > > > > diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c > > index fce412234d10..47a917038f58 100644 > > --- a/drivers/video/backlight/pwm_bl.c > > +++ b/drivers/video/backlight/pwm_bl.c > > @@ -531,12 +531,10 @@ static int pwm_backlight_probe(struct platform_device *pdev) > > if (!state.period && (data->pwm_period_ns > 0)) > > state.period = data->pwm_period_ns; > > > > - ret = pwm_apply_state(pb->pwm, &state); > > - if (ret) { > > - dev_err(&pdev->dev, "failed to apply initial PWM state: %d\n", > > - ret); > > - goto err_alloc; > > - } > > + /* > > + * No need to apply initial state, except in the error path. > > Why do you want to modify the PWM in the error path? I would have > expected not touching it at all in .probe() is fine?! > > > + * State will be applied by backlight_update_status() on success. > > + */ > > > > memset(&props, 0, sizeof(struct backlight_properties)); > > > > Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König | > Industrial Linux Solutions | https://www.pengutronix.de/ |
