[Intel-gfx] [PATCH v2 5/5] drm/i915: Force DPCD backlight mode on X1 Extreme 2nd Gen 4K AMOLED panel

[Jani Nikula]

On Wed, 15 Jan 2020, Lyude Paul <lyude at redhat.com> wrote:
> sigh… so I just went through the correspondence with the vendor I mentioned
> and unfortunately the answer is still unclear. It looks like that for some of
> these panels there might actually be some bits in the EDID (!?!?) that are
> supposed to correspond to the backlight interface. weird. on top of that I'm
> not even sure if these EDID bits are actually standard. Interestingly enough
> it seems like they're also intending for some of their panels to be able to be
> used in both PWM and DPCD mode, and will eventually drop the PWM
> compatibility.
>
> Note this vendor isn't Lenovo, so I'm assuming that's probably why pwm mode
> doesn't work at all on this X1 extreme.
>
> That being said all I've seen are systems that don't specify this correctly in
> the vbt but do in the dpcd, so I'm going to go ahead and change this patch
> series over to using the dpcd by default instead. If this actually breaks any
> systems out there we can change the default behavior later. I will do a respin
> of the series asap (will have it on the list today or tommorrow, will merge
> after CI gives the OK).

Don't worry, nothing about displays really surprises me anymore.

I'm fine with the idea of trying to use the DPCD alone to enable aux
backlight. We need to try to make this work out of the box, without
module parameters.

Just make sure it's reasonably easy to revert in case issues do arise...

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Graphics Center