Re: [PATCH v4 02/16] drm/edid: Don't clear formats if using deep color

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

On Thu, Jan 20, 2022 at 04:16:11PM +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 is also broken with YUV444 if it's supported by the display, but
> DRM_EDID_HDMI_DC_Y444 isn't set. In such a case, the code will clear
> color_formats of the YUV444 support set previously in
> drm_parse_cea_ext(), but will not set it back.
> 
> Since the formats supported are already setup properly in
> drm_parse_cea_ext(), let's just remove the code modifying the formats in
> drm_parse_hdmi_deep_color_info()
> 
> Fixes: d0c94692e0a3 ("drm/edid: Parse and handle HDMI deep color modes.")
> Signed-off-by: Maxime Ripard <maxime@cerno.tech>

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> ---
>  drivers/gpu/drm/drm_edid.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 13644dd579b4..5085ef08c22d 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -5104,16 +5104,8 @@ static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,
>  		  connector->name, dc_bpc);
>  	info->bpc = dc_bpc;
>  
> -	/*
> -	 * Deep color support mandates RGB444 support for all video
> -	 * modes and forbids YCRCB422 support for all video modes per
> -	 * HDMI 1.3 spec.
> -	 */
> -	info->color_formats = DRM_COLOR_FORMAT_RGB444;
> -
>  	/* YCRCB444 is optional according to spec. */
>  	if (hdmi[6] & DRM_EDID_HDMI_DC_Y444) {
> -		info->color_formats |= DRM_COLOR_FORMAT_YCRCB444;
>  		DRM_DEBUG("%s: HDMI sink does YCRCB444 in deep color.\n",
>  			  connector->name);
>  	}
> -- 
> 2.34.1

-- 
Ville Syrjälä
Intel