[Intel-gfx] AVI infoframes: default aspect ratio/VIC for CEA modes

[Damien Lespiau]

On Wed, Nov 20, 2013 at 10:11:55PM +0000, Damien Lespiau wrote:
> On Wed, Nov 20, 2013 at 09:48:26PM +0000, Gohad, Tushar wrote:
> > Folks,
> > 
> > A newbie question - When filling in an HDMI AVI infoframe, how does
> > one correctly determine the "default" picture aspect ratio (and VIC)
> > for CEA modes that support multiple (4:3 and 16:9) aspect ratios.
> > 720x576p for example, corresponds to VIC 17 or 18:
> > 
> >         /* 17 - 720x576 at 50Hz */
> >         { DRM_MODE("720x576", DRM_MODE_TYPE_DRIVER, 27000, 720, 732,
> >                    796, 864, 0, 576, 581, 586, 625, 0,
> >                    DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),
> >           .vrefresh = 50, },
> >         /* 18 - 720x576 at 50Hz */
> >         { DRM_MODE("720x576", DRM_MODE_TYPE_DRIVER, 27000, 720, 732,
> >                    796, 864, 0, 576, 581, 586, 625, 0,
> >                    DRM_MODE_FLAG_NHSYNC | DRM_MODE_FLAG_NVSYNC),
> >           .vrefresh = 50, },
> > 
> > Should the "picture aspect ratio" information be derived from sink
> > EDID (from detailed/cvt/standard timings)? .. possibly in
> > drm_add_edid_modes() and store the picture aspect ratio in
> > drm_display_mode perhaps, for later use?  Trying to get a better
> > understanding of how this usually works.
> 
> Oh no! someone finally discovered it! Yes, we are totally missing the
> picture aspect ratio information from the CEA modes. It's been on my
> TODO list for a couple of month but not exactly high priority. If we
> want to get a stab a it, we'll review the patches :)

I realized that I did not actually answer the question. The CEA modes
come with their defined aspect ratio, it's part of the CEA 861 standard.
In this case VIC 17 is 4:3, VIC 18 is 16:9.

-- 
Damien