Re: [PATCH 2/5] drm/edid: Introduce drm_default_rgb_quant_range()

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

On Sat, Jan 21, 2017 at 06:50:57AM +1100, Eric Anholt wrote:
> ville.syrjala@linux.intel.com writes:
> 
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Make the code selecting the RGB quantization range a little less magicy
> > by wrapping it up in a small helper.
> 
> This series seems good.  I won't have the ability to test it on vc4
> within a reasonable time frame, so you can add an Acked-by from me if
> you'd like.  Just one comment that you can take or leave:
> 
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/drm_edid.c        | 18 ++++++++++++++++++
> >  drivers/gpu/drm/i915/intel_dp.c   |  4 +++-
> >  drivers/gpu/drm/i915/intel_hdmi.c |  3 ++-
> >  drivers/gpu/drm/vc4/vc4_hdmi.c    |  4 +++-
> >  include/drm/drm_edid.h            |  2 ++
> >  5 files changed, 28 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> > index 4ff04aa84dd0..304c583b8000 100644
> > --- a/drivers/gpu/drm/drm_edid.c
> > +++ b/drivers/gpu/drm/drm_edid.c
> > @@ -3768,6 +3768,24 @@ bool drm_rgb_quant_range_selectable(struct edid *edid)
> >  }
> >  EXPORT_SYMBOL(drm_rgb_quant_range_selectable);
> >  
> > +/**
> > + * drm_default_rgb_quant_range - default RGB quantization range
> > + * @mode: display mode
> > + *
> > + * Determine the default RGB quantization range for the mode,
> > + * as specified in CEA-861.
> > + *
> > + * Return: The default RGB quantization range for the mode
> > + */
> > +enum hdmi_quantization_range
> > +drm_default_rgb_quant_range(const struct drm_display_mode *mode)
> > +{
> > +	return drm_match_cea_mode(mode) > 1 ?
> > +		HDMI_QUANTIZATION_RANGE_LIMITED :
> > +		HDMI_QUANTIZATION_RANGE_FULL;
> 
> It might be nice to add a comment here like
> 
> /* All CEA modes other than VIC 1 use limited quantization range. */
> 
> When I first had to put this logic in vc4, I was surprised by it and
> figured that it was an off-by-one bug in code that was trying to say "if
> it's any CEA mode then it should be limited range"

Seems like a good idea. I could even try to dig up a specific spec
quote perhaps? And if I can't find anything succinct in the spec we
can always go with your proposal.

> 
> 
> > +}
> > +EXPORT_SYMBOL(drm_default_rgb_quant_range);

-- 
Ville Syrjälä
Intel OTC
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