drm: edid: Refactor HDMI VSDB detection

There are two slightly different pieces of code for HDMI VSDB
detection. Unify the code into a single helper function.

Also fix a bug where drm_detect_hdmi_monitor() would stop looking
for the HDMI VSDB after the first vendor specific block is found,
whether or not that block happened to be the HDMI VSDB. The
standard allows for any number of vendor specific blocks to be
present.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_edid.c

@@ -1621,6 +1621,21 @@ monitor_name(struct detailed_timing *t, void *data)
 		*(u8 **)data = t->data.other_data.data.str.str;
 }
 
+static bool cea_db_is_hdmi_vsdb(const u8 *db)
+{
+	int hdmi_id;
+
+	if (cea_db_tag(db) != VENDOR_BLOCK)
+		return false;
+
+	if (cea_db_payload_len(db) < 5)
+		return false;
+
+	hdmi_id = db[1] | (db[2] << 8) | (db[3] << 16);
+
+	return hdmi_id == HDMI_IDENTIFIER;
+}
+
 /**
  * drm_edid_to_eld - build ELD from EDID
  * @connector: connector corresponding to the HDMI/DP sink
@@ -1693,7 +1708,7 @@ void drm_edid_to_eld(struct drm_connector *connector, struct edid *edid)
 				break;
 			case VENDOR_BLOCK:
 				/* HDMI Vendor-Specific Data Block */
-				if (dbl >= 5 && db[1] == 0x03 && db[2] == 0x0c && db[3] == 0)
+				if (cea_db_is_hdmi_vsdb(db))
 					parse_hdmi_vsdb(connector, db);
 				break;
 			default:
@@ -1778,35 +1793,26 @@ EXPORT_SYMBOL(drm_select_eld);
 bool drm_detect_hdmi_monitor(struct edid *edid)
 {
 	u8 *edid_ext;
-	int i, hdmi_id;
+	int i;
 	int start_offset, end_offset;
-	bool is_hdmi = false;
 
 	edid_ext = drm_find_cea_extension(edid);
 	if (!edid_ext)
-		goto end;
+		return false;
 
 	if (cea_db_offsets(edid_ext, &start_offset, &end_offset))
-		goto end;
+		return false;
 
 	/*
 	 * Because HDMI identifier is in Vendor Specific Block,
 	 * search it from all data blocks of CEA extension.
 	 */
 	for_each_cea_db(edid_ext, i, start_offset, end_offset) {
-		/* Find vendor specific block */
-		if (cea_db_tag(&edid_ext[i]) == VENDOR_BLOCK) {
-			hdmi_id = edid_ext[i + 1] | (edid_ext[i + 2] << 8) |
-				  edid_ext[i + 3] << 16;
-			/* Find HDMI identifier */
-			if (hdmi_id == HDMI_IDENTIFIER)
-				is_hdmi = true;
-			break;
-		}
+		if (cea_db_is_hdmi_vsdb(&edid_ext[i]))
+			return true;
 	}
 
-end:
-	return is_hdmi;
+	return false;
 }
 EXPORT_SYMBOL(drm_detect_hdmi_monitor);