[PATCH] drm/edid: fix CEA extension byte #3 parsing

[Ville Syrjälä]

On Wed, Mar 23, 2022 at 12:04:38PM +0200, Jani Nikula wrote:
> Only an EDID CEA extension has byte #3, while the CTA DisplayID Data
> Block does not. Don't interpret bogus data for color formats.

I think what we might want eventually is a cleaner split between
the CTA data blocks vs. the rest of the EDID CTA ext block. Only
the former is relevant for DisplayID.

But for a bugfix we want to keep it simple.

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

> 
> For most displays it's probably an unlikely scenario you'd have a CTA
> DisplayID Data Block without a CEA extension, but they do exist.
> 
> Fixes: e28ad544f462 ("drm/edid: parse CEA blocks embedded in DisplayID")
> Cc: <stable at vger.kernel.org> # v4.15
> Cc: Shawn C Lee <shawn.c.lee at intel.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>
> 
> ---
> 
> commit e28ad544f462 was merged in v5.3, but it has Cc: stable for v4.15.
> 
> This is also fixed in my CEA data block iteration series [1], but we'll
> want the simple fix for stable first.
> 
> Hum, CTA is formerly CEA, I and the code seem to use both, should we use
> only one or the other?

And before CEA it was called EIA (IIRC). Dunno if we also use that name
somewhere.

If someone cares enough I guess we could rename everything to "cta".

> 
> [1] https://patchwork.freedesktop.org/series/101659/
> ---
>  drivers/gpu/drm/drm_edid.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index 561f53831e29..ccf7031a6797 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -5187,10 +5187,14 @@ static void drm_parse_cea_ext(struct drm_connector *connector,
>  
>  	/* The existence of a CEA block should imply RGB support */
>  	info->color_formats = DRM_COLOR_FORMAT_RGB444;
> -	if (edid_ext[3] & EDID_CEA_YCRCB444)
> -		info->color_formats |= DRM_COLOR_FORMAT_YCBCR444;
> -	if (edid_ext[3] & EDID_CEA_YCRCB422)
> -		info->color_formats |= DRM_COLOR_FORMAT_YCBCR422;
> +
> +	/* CTA DisplayID Data Block does not have byte #3 */
> +	if (edid_ext[0] == CEA_EXT) {
> +		if (edid_ext[3] & EDID_CEA_YCRCB444)
> +			info->color_formats |= DRM_COLOR_FORMAT_YCBCR444;
> +		if (edid_ext[3] & EDID_CEA_YCRCB422)
> +			info->color_formats |= DRM_COLOR_FORMAT_YCBCR422;
> +	}
>  
>  	if (cea_db_offsets(edid_ext, &start, &end))
>  		return;
> -- 
> 2.30.2

-- 
Ville Syrjälä
Intel