Re: [PATCH v6 2/7] drm/edid: prepare for VESA vendor-specific data block extension

[Yaroslav]

On 2025-11-26 10:13, Jani Nikula wrote:
On Wed, 26 Nov 2025, Yaroslav Bolyukin <i...@lach.pw> wrote:
Current VESA vendor-specific block parsing expects real block size to be
the same as the defined struct size, use real offsets in conditionals
instead to add struct fields in future commits.

Signed-off-by: Yaroslav Bolyukin <i...@lach.pw>

I think this is something we want to backport, since MSO would break
with bigger vendor-specific blocks, and that leads to black screens on
MSO displays.


Not sure why would we want to backport that if we don't backport the 
other changes, old kernels will just have the broken implementation, 
which in reality affects almost no body, given that there were no bug 
reports
Cc: sta...@vger.kernel.org
Reviewed-by: Jani Nikula <jani.nik...@intel.com>

---
  drivers/gpu/drm/drm_edid.c | 28 ++++++++++++----------------
  1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 64f7a94dd9e4..a52fd6de9327 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -6544,7 +6544,7 @@ static void drm_parse_vesa_specific_block(struct 
drm_connector *connector,
        if (oui(vesa->oui[0], vesa->oui[1], vesa->oui[2]) != VESA_IEEE_OUI)
                return;
  
-	if (sizeof(*vesa) != sizeof(*block) + block->num_bytes) {
+       if (block->num_bytes < 5) {
                drm_dbg_kms(connector->dev,
                            "[CONNECTOR:%d:%s] Unexpected VESA vendor block 
size\n",
                            connector->base.id, connector->name);
@@ -6567,24 +6567,20 @@ static void drm_parse_vesa_specific_block(struct 
drm_connector *connector,
                break;
        }
  
-	if (!info->mso_stream_count) {
-               info->mso_pixel_overlap = 0;
-               return;
-       }
-
-       info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP, 
vesa->mso);
-       if (info->mso_pixel_overlap > 8) {
+       if (info->mso_stream_count) {
+               info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP, 
vesa->mso);
+               if (info->mso_pixel_overlap > 8) {
+                       drm_dbg_kms(connector->dev,
+                                   "[CONNECTOR:%d:%s] Reserved MSO pixel overlap 
value %u\n",
+                                   connector->base.id, connector->name,
+                                   info->mso_pixel_overlap);
+                       info->mso_pixel_overlap = 8;
+               }
                drm_dbg_kms(connector->dev,
-                           "[CONNECTOR:%d:%s] Reserved MSO pixel overlap value 
%u\n",
+                           "[CONNECTOR:%d:%s] MSO stream count %u, pixel overlap 
%u\n",
                            connector->base.id, connector->name,
-                           info->mso_pixel_overlap);
-               info->mso_pixel_overlap = 8;
+                           info->mso_stream_count, info->mso_pixel_overlap);
        }
-
-       drm_dbg_kms(connector->dev,
-                   "[CONNECTOR:%d:%s] MSO stream count %u, pixel overlap %u\n",
-                   connector->base.id, connector->name,
-                   info->mso_stream_count, info->mso_pixel_overlap);
  }
  
  static void drm_update_vesa_specific_block(struct drm_connector *connector,