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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Nov 21, 2013 at 02:48:55AM +0000, Gohad, Tushar wrote:
> > On Wed, Nov 20, 2013 at 11:45:03PM +0000, Gohad, Tushar wrote:
> > > > > On Wed, Nov 20, 2013 at 09:48:26PM +0000, Gohad, Tushar wrote:
> > > > > > Folks,
> > > > > >
> > > > > > 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
> > > > > :)
> > >
> 
> > > Thanks Damien.  Sure, I can come up with something quick.  Is the idea
> > > then to store aspect ratio information in drm_display_mode, possibly
> > > as a separate member or as a hint that's part of mode->flags?
> > 
> > It seems natural to extend those flags to describe the picture aspect ratio (that
> > why dri-devel is in Cc., touching core DRM).
> 
> Cc: dri-devel
> 
> To start with we can use a single bit in drm_display_mode->flags to distinguish 16:9 vs 4:3.

I must admit I haven't really looked into the matter, but do we actually
need any mode bits? Would it be enoguh to just have a property that
allows the user to specify the picture aspect ratio?

-- 
Ville Syrjälä
Intel OTC