Re: AVI infoframes: default aspect ratio/VIC for CEA modes

[Damien Lespiau <damien.lespiau@intel.com>]

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@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@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 :)

> As an aside, to match VIC correctly, shouldn't drm_match_cea_mode()
> take into account picture aspect ratio as well?

Yes.

-- 
Damien