Re: [PATCH] drm/panel-edp: Change the KD116N2930A15 panel enable delay

[Haikun Zhou]

Hi Doug, thank you very much for your reply,

On Wed, Jul 1, 2026 at 1:33 AM Doug Anderson <dianders@xxxxxxxxxxxx> wrote:
>
> Hi,
>
> On Sun, Jun 28, 2026 at 8:09 PM Haikun Zhou
> <zhouhaikun5@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Due to panel characteristics, when the panel wakes up from the S3, the
> > main link data is not yet ready when the backlight turns on, causing
> > a garbage appearance on the screen. Delaying the backlight by 1000ms
> > can avoid this issue.
> >
> > Signed-off-by: Haikun Zhou <zhouhaikun5@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/panel/panel-edp.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
>
> This really doesn't feel right; it seems like a hack papering over a
> problem whose root cause hasn't been found. If nothing else, what does
> "S3" have to do with anything? The panel isn't left powered on during
> S3, right? So, as far as the panel is concerned, S3 should be the same
> as S5. Why would you see this noise only coming out of S3?
>
> -Doug

Yes, this screen issue isn't limited to the S3; the backlight turning
on first and then
displaying garbage isn't limited to this issue. On Chromebooks, the
same phenomenon occurs
when the backlight is completely turned off and then back on.
Measurements with EE revealed
that when the backlight is on, the main link data is already being
transmitted but is still unstable.
Turning on the backlight at this time causes the screen to display garbage.
We had to add sufficient backlight delay to fix this issue, and while
we could modify it in the DTS
settings, since this is a screen-related problem, we wanted to fix it
from the driver.