[led-backlight] default-brightness-level issue

[pgeiem]

On Thursday, April 29, 2021 1:00 PM, Daniel Thompson <daniel.thompson at linaro.org> wrote:

> On Fri, Apr 23, 2021 at 01:04:23PM +0000, pgeiem wrote:
>
> > Dear all,
> > On a custom board I have a simple DPI panel. Panel's backlight is
> > drive with an I2C led driver (PCA9632). led-backlight driver is sued
> > to manage this as a backlight.
> > When using brightness-levels and default-brightness-level the
> > backlight stay turned-off even if manually trying to set a different
> > index value to brightness through sysfs.
> > I traced this issue as follow: When led_bl_update_status() is called
> > the brightness value is returned from backlight_get_brightness() which
> > call backlight_is_blank(). In my case backlight_is_blank() return true
> > due to props.power = FB_BLANK_POWERDOWN which is != FB_BLANK_UNBLANK.
> > I traced why at startup props.power is FB_BLANK_POWERDOWN and found
> > that in led_bl_probe() when a default brightness is set (>0)
> > props.power is set to FB_BLANK_POWERDOWN which seems incorrect to me.
> > I made the small change below and default brightness is correctly used
> > at startup. I am not really sure this is an issue and if my change is
> > correct or if I am doing something incorrect somewhere else. So I
> > first would like to get your opinion on this and if correct will send
> > a patch.
>
> Makes sense. Please send this as a patch.
>
> Daniel.

I finally believe this was correct.

A link between the panel and the backlight was missing in dts. With this link the backlight is turned on (props.power = FB_BLANK_UNBLANK) from drm_panel_enable function after enabling the panel.

Let me know if you disagree and still believe I should send the patch.

Patrick