Re: [PATCH v2 01/14] drm/edid: Don't clear YUV422 if using deep color

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

On Tue, Jan 11, 2022 at 04:55:35PM +0100, Maxime Ripard wrote:
> Hi Ville,
> 
> Thanks for your review
> 
> On Wed, Dec 15, 2021 at 03:48:39PM +0200, Ville Syrjälä wrote:
> > On Wed, Dec 15, 2021 at 01:43:53PM +0100, Maxime Ripard wrote:
> > > The current code, when parsing the EDID Deep Color depths, that the
> > > YUV422 cannot be used, referring to the HDMI 1.3 Specification.
> > > 
> > > This specification, in its section 6.2.4, indeed states:
> > > 
> > >   For each supported Deep Color mode, RGB 4:4:4 shall be supported and
> > >   optionally YCBCR 4:4:4 may be supported.
> > > 
> > >   YCBCR 4:2:2 is not permitted for any Deep Color mode.
> > > 
> > > This indeed can be interpreted like the code does, but the HDMI 1.4
> > > specification further clarifies that statement in its section 6.2.4:
> > > 
> > >   For each supported Deep Color mode, RGB 4:4:4 shall be supported and
> > >   optionally YCBCR 4:4:4 may be supported.
> > > 
> > >   YCBCR 4:2:2 is also 36-bit mode but does not require the further use
> > >   of the Deep Color modes described in section 6.5.2 and 6.5.3.
> > > 
> > > This means that, even though YUV422 can be used with 12 bit per color,
> > > it shouldn't be treated as a deep color mode.
> > > 
> > > This deviates from the interpretation of the code and comment, so let's
> > > fix those.
> > > 
> > > Fixes: d0c94692e0a3 ("drm/edid: Parse and handle HDMI deep color modes.")
> > > Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> > > ---
> > >  drivers/gpu/drm/drm_edid.c | 5 ++---
> > >  1 file changed, 2 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> > > index 12893e7be89b..e57d1b8cdaaa 100644
> > > --- a/drivers/gpu/drm/drm_edid.c
> > > +++ b/drivers/gpu/drm/drm_edid.c
> > > @@ -5106,10 +5106,9 @@ static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,
> > >  
> > >  	/*
> > >  	 * Deep color support mandates RGB444 support for all video
> > > -	 * modes and forbids YCRCB422 support for all video modes per
> > > -	 * HDMI 1.3 spec.
> > > +	 * modes.
> > >  	 */
> > > -	info->color_formats = DRM_COLOR_FORMAT_RGB444;
> > > +	info->color_formats |= DRM_COLOR_FORMAT_RGB444;
> > >  
> > >  	/* YCRCB444 is optional according to spec. */
> > >  	if (hdmi[6] & DRM_EDID_HDMI_DC_Y444) {
> > 
> > This whole code seems pretty much wrong. What it tries to do (I think)
> > is make sure we don't use deep color with YCbCr 4:4:4 unless supported.
> > But what it actually does is also disable YCbCr 4:4:4 8bpc when deep
> > color is not supported for YCbCr 4:4:4.
> > 
> > I think what we want is to just get rid of this color_formats stuff here
> > entirely and instead have some kind of separate tracking of RGB 4:4:4 vs.
> > YCbCr 4:4:4 deep color capabilities.
> 
> I'm sorry, I'm not entirely sure to understand what you're suggesting
> here. Do you want to get ride of info->color_formats entirely?

I think color_formats can stay (assuming it's actually useful for
something), but we need separate tracking for supported RGB 4:4:4
vs. YCbCr 4:4:4 deep color modes.

-- 
Ville Syrjälä
Intel