HDMI Aspect Ratio

[Ville Syrjälä]

On Thu, Oct 19, 2017 at 01:08:05PM -0400, Alex Deucher wrote:
> On Thu, Oct 19, 2017 at 12:32 PM, Rob Clark <robdclark at gmail.com> wrote:
> > On Wed, Oct 18, 2017 at 4:06 PM, Lloyd Atkinson <latkinso at codeaurora.org> wrote:
> >> Hi folks,
> >>
> >> We're looking at 4K HDMI mode support, and noticed aspect ratio support
> >> is in flux.
> >>
> >> Aspect ratio parsing was added to the mode:
> >> https://patchwork.kernel.org/patch/9271401/
> >>
> >> But later reverted:
> >> https://patchwork.kernel.org/patch/9410765/
> >>
> >> We're finding that since aspect ratio information isn't supported, modes
> >> conflict, and the userspace isn't able to see the full list of modes.
> >>
> >> Similarly, there's a case where two modes differ only by aspect_ratio
> >> and vrefresh. In drm_edid.c, within drm_display_mode_from_vic_index,
> >> newmode->vrefresh is forcibly being cleared to 0. Since refresh rate is
> >> forced to 0, and aspect ratio isn’t considered in general, the modes
> >> collide and we can’t advertise one of the modes.
> >>
> >> https://github.com/torvalds/linux/blob/v4.14-rc4/drivers/gpu/drm/drm_edid.c#L3153
> >>
> >> Have there been any follow-up discussions on this topic?
> >>
> >> What is the reason to clear the vrefresh within
> >> drm_display_mode_from_vic_index?
> >
> > +Ville who might remember the history..
> >
> > I don't remember if we found a userspace app that was broken, or if
> > reverting was an "abundance of caution" thing (which is equally valid,
> > it is basically impossible to track down and test "all of
> > userspace"..)
> >
> 
> Wasn't there an issue with SNA?

Exposing the aspect ratio flags broke sna, at least.

-- 
Ville Syrjälä
Intel OTC