[PATCH] drm/i915/display: Fixed a screen flickering when turning on display from off

[Ville Syrjälä]

On Wed, Mar 06, 2024 at 12:19:42PM +0200, Jani Nikula wrote:
> On Wed, 06 Mar 2024, gareth.yu at intel.com wrote:
> > From: Gareth Yu <gareth.yu at intel.com>
> >
> > Turn on the panel from zero brightness of the last state, the panel was set
> > a maximum PWM in the flow. Once the panel initialization is completed, the
> > backlight is restored to zero brightness. There is a flckering generated.
> 
> Please be more precise in describing what exactly happens and
> when. Driver probe? Modeset? What restores backlight to zero brightness?
> 
> Better yet, please file a bug at fdo gitlab, attach full dmesg with
> debugs, etc.
> 
> Before we had the concept of minimum brightness, the minimum was always
> 0. And the check was:
> 
> 	if (level == 0)
> 		level = max;
> 
> Historically, the point was, if you're enabling the display and
> backlight, you don't want it to be at 0 brightness, because for most
> displays that means a black screen.

I think that hack was originally added becaue some silly
userspace thingy was setting the backlight level to 0 on
suspend/etc. and then forgetting to restore it back to a
sane value afterwards. Dunno if that nonsense behaviour
still persists to this day.

-- 
Ville Syrjälä
Intel