On Wed, 23 Mar 2022, Ville Syrjälä ville.syrjala@linux.intel.com wrote:

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.

Well, I just abstracted it all away in the CEA data block iteration series [1].

It'll be possible to add a different iteration initializer depending on what you want to iterate and where.

BR, Jani.

But for a bugfix we want to keep it simple.

Reviewed-by: Ville Syrjälä ville.syrjala@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@vger.kernel.org # v4.15 Cc: Shawn C Lee shawn.c.lee@intel.com Cc: Ville Syrjälä ville.syrjala@linux.intel.com Signed-off-by: Jani Nikula jani.nikula@intel.com

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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".

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[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