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

[Maxime Ripard]

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 at 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?

Maxime
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