drm/edid: Try harder to fix up base EDID blocks

Requiring the first byte of the EDID base block header to be 0 means we
don't fix up as many transfer errors as we could.  Instead have the
callers specify whether it's meant to be block 0 or not, and
conditionally run header fixup based on that.

Bugzilla: https://bugzilla.redhat.com/812890
Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Alex Deucher <alexdeucher@gmail.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_edid.c

@@ -149,13 +149,13 @@ EXPORT_SYMBOL(drm_edid_header_is_valid);
  * Sanity check the EDID block (base or extension).  Return 0 if the block
  * doesn't check out, or 1 if it's valid.
  */
-bool drm_edid_block_valid(u8 *raw_edid)
+bool drm_edid_block_valid(u8 *raw_edid, int block)
 {
 	int i;
 	u8 csum = 0;
 	struct edid *edid = (struct edid *)raw_edid;
 
-	if (raw_edid[0] == 0x00) {
+	if (block == 0) {
 		int score = drm_edid_header_is_valid(raw_edid);
 		if (score == 8) ;
 		else if (score >= 6) {
@@ -219,7 +219,7 @@ bool drm_edid_is_valid(struct edid *edid)
 		return false;
 
 	for (i = 0; i <= edid->extensions; i++)
-		if (!drm_edid_block_valid(raw + i * EDID_LENGTH))
+		if (!drm_edid_block_valid(raw + i * EDID_LENGTH, i))
 			return false;
 
 	return true;
@@ -299,7 +299,7 @@ drm_do_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter)
 	for (i = 0; i < 4; i++) {
 		if (drm_do_probe_ddc_edid(adapter, block, 0, EDID_LENGTH))
 			goto out;
-		if (drm_edid_block_valid(block))
+		if (drm_edid_block_valid(block, 0))
 			break;
 		if (i == 0 && drm_edid_is_zero(block, EDID_LENGTH)) {
 			connector->null_edid_counter++;
@@ -324,7 +324,7 @@ drm_do_get_edid(struct drm_connector *connector, struct i2c_adapter *adapter)
 				  block + (valid_extensions + 1) * EDID_LENGTH,
 				  j, EDID_LENGTH))
 				goto out;
-			if (drm_edid_block_valid(block + (valid_extensions + 1) * EDID_LENGTH)) {
+			if (drm_edid_block_valid(block + (valid_extensions + 1) * EDID_LENGTH, j)) {
 				valid_extensions++;
 				break;
 			}

include/drm/drm_crtc.h

@@ -1012,7 +1012,7 @@ extern int drm_add_modes_noedid(struct drm_connector *connector,
 				int hdisplay, int vdisplay);
 
 extern int drm_edid_header_is_valid(const u8 *raw_edid);
-extern bool drm_edid_block_valid(u8 *raw_edid);
+extern bool drm_edid_block_valid(u8 *raw_edid, int block);
 extern bool drm_edid_is_valid(struct edid *edid);
 struct drm_display_mode *drm_mode_find_dmt(struct drm_device *dev,
 					   int hsize, int vsize, int fresh,