On Thu, Jul 08, 2021 at 11:10:58AM +0200, Marek Vasut wrote:
> The note in c2adda27d202f ("video: backlight: Add of_find_backlight helper
> in backlight.c") says that gpio-backlight uses brightness as power state.
> Other backlight drivers do not, so limit this workaround to gpio-backlight.
>
> This fixes the case where e.g. pwm-backlight can perfectly well be set to
> brightness 0 on boot in DT, which without this patch leads to the display
> brightness to be max instead of off.
>
> Fixes: c2adda27d202f ("video: backlight: Add of_find_backlight helper in backlight.c")
> Signed-off-by: Marek Vasut <marex@xxxxxxx>
> Cc: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> Cc: Meghana Madhyastha <meghana.madhyastha@xxxxxxxxx>
> Cc: Noralf Trønnes <noralf@xxxxxxxxxxx>
> Cc: Sean Paul <seanpaul@xxxxxxxxxxxx>
> Cc: Thierry Reding <treding@xxxxxxxxxx>
I have to admit that this patch really does makes it clear just how
nasty the hack in of_find_backlight() currently is.
Moreover I think it is also be obsolete. gpio-backlight power mode
handling was pretty broken when this code was introduced. It was fixed
in 2019 by ec665b756e6f ("backlight: gpio backlight: Correct initial
power state handling") by trying to match the behaviour of PWM
backlight. The new code always sets the brightness to 1 so I think we
can just remove the hack from of_find_backlight() since I think it is
unreachable.
Daniel.
> ---
> drivers/video/backlight/backlight.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 537fe1b376ad7..dfb66171dec41 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -676,6 +676,7 @@ EXPORT_SYMBOL(of_find_backlight_by_node);
> static struct backlight_device *of_find_backlight(struct device *dev)
> {
> struct backlight_device *bd = NULL;
> + bool is_gpio_backlight = false;
> struct device_node *np;
>
> if (!dev)
> @@ -685,6 +686,8 @@ static struct backlight_device *of_find_backlight(struct device *dev)
> np = of_parse_phandle(dev->of_node, "backlight", 0);
> if (np) {
> bd = of_find_backlight_by_node(np);
> + is_gpio_backlight =
> + of_device_is_compatible(np, "gpio-backlight");
> of_node_put(np);
> if (!bd)
> return ERR_PTR(-EPROBE_DEFER);
> @@ -692,7 +695,7 @@ static struct backlight_device *of_find_backlight(struct device *dev)
> * Note: gpio_backlight uses brightness as
> * power state during probe
> */
> - if (!bd->props.brightness)
> + if (is_gpio_backlight && !bd->props.brightness)
> bd->props.brightness = bd->props.max_brightness;
> }
> }
> --
> 2.30.2
