Re: [PATCH] backlight: pwm_bl: Avoid backlight flicker applying initial PWM state
From: Uwe Kleine-König <hidden>
Date: 2023-10-18 21:07:55
Also in:
dri-devel, linux-pwm, lkml
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?
quoted hunk ↗ jump to hunk
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@pengutronix.de> --- 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/ |
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