| Message ID | 2a4c94417f024cbafc5d4ca0a74e4617fc4325d1.1654674560.git.jani.nikula@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/edid: expand on struct drm_edid usage | expand |
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
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; if (iter->end < 4 || iter->end > 127) continue;
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(-)