On Wed, Jun 08, 2022 at 10:50:31AM +0300, Jani Nikula wrote:
The CTA Data Block Collection is valid only for CTA extension version 3. In versions 1 and 2, it is a reserved block, which we ignore.
The DTD start offset (byte 2, or d in CTA-861 spec), which determines the CTA Data Block Collection size, is specified slightly differently for different versions:
Version 1: d = offset for the byte following the reserved data block. If no data is provided in the reserved data block, then d=4. If no DTDs are provided, then d=0
Version 2: d = offset for the byte following the reserved data block. If no data is provided in the reserved data block, then d=4. If d=0, then no detailed timing descriptors are provided, and no data is provided in the reserved data block.
Version 3: d = offset for the byte following the data block collection. If no data is provided in the data block collection, then d=4. If d=0, then no detailed timing descriptors are provided, and no data is provided in the data block collection.
Ever since commit 9e50b9d55e9c ("drm: edid: Add some bounds checking"), we've interpreted 0 to mean there are no DTDs but it's all Data Blocks. Per the spec, Data Blocks are only valid for version 3, where we should interpret 0 to mean there are no data blocks.
Follow the spec (and hope the EDIDs follow it too).
Cc: Ville Syrjälä ville.syrjala@linux.intel.com Signed-off-by: Jani Nikula jani.nikula@intel.com
drivers/gpu/drm/drm_edid.c | 2 -- 1 file changed, 2 deletions(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c index 929fc0e46751..c57f6333ea7d 100644 --- a/drivers/gpu/drm/drm_edid.c +++ b/drivers/gpu/drm/drm_edid.c @@ -4498,8 +4498,6 @@ static const void *__cea_db_iter_edid_next(struct cea_db_iter *iter)
iter->index = 4; iter->end = ext[2];
if (iter->end == 0)iter->end = 127;
Not really sure how I came up with this interpretation of the spec.
Looks like I at least fixed up the 18byte descriptor parsing correctly in commit 7304b9810a73 ("drm/edid: Check the number of detailed timing descriptors in the CEA ext block")
Reviewed-by: Ville Syrjälä ville.syrjala@linux.intel.com
if (iter->end < 4 || iter->end > 127) continue;-- 2.30.2