[Intel-gfx] [PATCH] drm/i915/display: Re-add check for low voltage sku for max dp source rate

[Jason A. Donenfeld]

Hi Jani,

On Mon, Jun 13, 2022 at 02:05:17PM +0300, Jani Nikula wrote:
> On Mon, 13 Jun 2022, "Jason A. Donenfeld" <Jason at zx2c4.com> wrote:
> > This reverts commit 73867c8709b569cdd7fda67f01dfe02c8d055521, which, on
> > an i7-11850H iGPU with a Thinkpad X1 Extreme Gen 4, attached to a LG
> > LP160UQ1-SPB1 embedded panel, causes wild flickering glitching
> > technicolor pyrotechnics on resumption from suspend. The display shows
> > strobing colors in an utter disaster explosion of pantone, as though
> > bombs were dropped on the leprechauns at the base of the rainbow.
> >
> > Rebooting the machine fixes the issue, presumably because the display is
> > initialized by firmware rather than by i915. Otherwise, the GPU appears
> > to work fine.
> >
> > Bisection traced it back to this commit, which makes sense given the
> > issues.
> 
> Thanks for putting in the effort to bisect, and the patch.
> 
> As the commit message of the regressing commit suggests, the VBT (Video
> BIOS Tables) should contain the info about max rates, filled in by the
> OEM. Unfortunately, we were missing some of the checks,
> e.g. 24b8b74eb2eb ("drm/i915: Parse max link rate from the eDP BDB
> block") added to drm-intel-next just recently.
> 
> Unfortunately, gitlab is down today so I can't check if you already
> tried drm-tip [1]; that might be helpful. Also, attaching
> /sys/kernel/debug/dri/0/i915_vbt might be useful to see if the
> limitation is there.
> 
> If your system works with the limitations from VBT, *and* the commits
> adding that support are trivial to backport to v5.19, I'm inclined to do
> that instead of the revert. But obviously the revert is the way to go if
> that doesn't happen.

I checked with drm-tip last week when I filed the bug, and I just
remerged the latest today, just in case there was anything new, and
alas, the problem still occurs.

Jason