drm/edid: Fix up partially corrupted headers

We'll still fail the block if it fails the EDID checksum though.

See also: http://bugzilla.redhat.com/534120

Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_edid.c

@@ -123,23 +123,33 @@ static const u8 edid_header[] = {
  */
 static bool edid_is_valid(struct edid *edid)
 {
-	int i;
+	int i, score = 0;
 	u8 csum = 0;
 	u8 *raw_edid = (u8 *)edid;
 
-	if (memcmp(edid->header, edid_header, sizeof(edid_header)))
-		goto bad;
-	if (edid->version != 1) {
-		DRM_ERROR("EDID has major version %d, instead of 1\n", edid->version);
+	for (i = 0; i < sizeof(edid_header); i++)
+		if (raw_edid[i] == edid_header[i])
+			score++;
+
+	if (score == 8) ;
+	else if (score >= 6) {
+		DRM_DEBUG("Fixing EDID header, your hardware may be failing\n");
+		memcpy(raw_edid, edid_header, sizeof(edid_header));
+	} else
 		goto bad;
-	}
+
 	for (i = 0; i < EDID_LENGTH; i++)
 		csum += raw_edid[i];
 	if (csum) {
 		DRM_ERROR("EDID checksum is invalid, remainder is %d\n", csum);
 		goto bad;
 	}
 
+	if (edid->version != 1) {
+		DRM_ERROR("EDID has major version %d, instead of 1\n", edid->version);
+		goto bad;
+	}
+
 	if (edid->revision > 4)
 		DRM_DEBUG("EDID minor > 4, assuming backward compatibility\n");