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@xxxxxxxxxx>
> ---
> 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.
--
Ville Syrjälä
Intel
