[Intel-gfx] [PATCH 2/6] drm/i915: Pick the first mode from EDID as the fixed mode when there is no preferred mode

[Adam Jackson]

On Thu, 2019-03-21 at 15:24 +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Some monitors apparently forget to mark any mode as preferred in the
> EDID. In this particular case we have a very generic looking ID
> "PNP Model 0 Serial Number 4" / "LVDS 800x600" so a specific quirk
> doesn't seem particularly wise. Also the quirk we have
> (EDID_QUIRK_FIRST_DETAILED_PREFERRED) is actually defunct so we'd
> have to fix it first.
> 
> When there is no preferred mode we currently fall back to the VBT.
> That approach fails us here as the VBT mode is 1024x768 whereas
> the panel resolution is 800x600. So instead of falling back to the
> VBT when there is no preferred mode let's just pick the first
> probed mode. Only if the EDID provided no modes we fall back to
> the VBT.
> 
> For this machine the VBIOS would appear to select the 800x600
> 60Hz EST mode rather than the first detailed mode (which is
> the new fallback will pick). The two modes differ only by
> having opposite sync polarities, which does not seem to matter
> to the panel in question.

Took me a moment to realize this was only about panels on i915, and not
any monitor/connector with no preferred modes. Looks sane to me though.

Reviewed-by: Adam Jackson <ajax at redhat.com>

- ajax