[PATCH 1/2] drm/edid: Don't look for CEA data blocks in CEA ext block rev < 3

[Ville Syrjala]

From: Ville Syrjälä <ville.syrjala at linux.intel.com>

CEA ext block revisions 1 and 2 do not contain the data block
collection. Instead that section of the extension block is
marked as reserved for 8 byte timing descriptors. Revision 3
changed it to contain the CEA data block collection instead.

Most places that iterate the data blocks already check for
revision >= 3, but drm_detect_hdmi_monitor() and
drm_detect_monitor_audio() do not. So in theory when encountering
rev 1 or 2 CEA extension block they could end up misinterpreting
whatever data is in the reserved section as CEA data blocks.

Let's have cea_db_offsets() do the revision check so that the
callers don't even have worry about it.

Cc: Jean Delvare <jdelvare at suse.de>
Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
---
 drivers/gpu/drm/drm_edid.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 82a4ceed3fcf..7b3072fc550b 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -3690,6 +3690,9 @@ cea_revision(const u8 *cea)
 static int
 cea_db_offsets(const u8 *cea, int *start, int *end)
 {
+	if (cea_revision(cea) < 3)
+		return -ENOTSUPP;
+
 	/* DisplayID CTA extension blocks and top-level CEA EDID
 	 * block header definitions differ in the following bytes:
 	 *   1) Byte 2 of the header specifies length differently,
-- 
2.21.0