drm/edid: check for HF-VSDB block

This patch implements a small function that finds if a
given CEA db is hdmi-forum vendor specific data block
or not.

V2: Rebase.
V3: Added R-B from Jose.
V4: Rebase
V5: Rebase
V6: Rebase
V7: Rebase
V8: Rebase
V9: Rebase
V10: Rebase

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1489404244-16608-3-git-send-email-shashank.sharma@intel.com

drivers/gpu/drm/drm_edid.c

@@ -3248,6 +3248,21 @@ static bool cea_db_is_hdmi_vsdb(const u8 *db)
 	return hdmi_id == HDMI_IEEE_OUI;
 }
 
+static bool cea_db_is_hdmi_forum_vsdb(const u8 *db)
+{
+	unsigned int oui;
+
+	if (cea_db_tag(db) != VENDOR_BLOCK)
+		return false;
+
+	if (cea_db_payload_len(db) < 7)
+		return false;
+
+	oui = db[3] << 16 | db[2] << 8 | db[1];
+
+	return oui == HDMI_FORUM_IEEE_OUI;
+}
+
 #define for_each_cea_db(cea, i, start, end) \
 	for ((i) = (start); (i) < (end) && (i) + cea_db_payload_len(&(cea)[(i)]) < (end); (i) += cea_db_payload_len(&(cea)[(i)]) + 1)
 

include/linux/hdmi.h

@@ -35,6 +35,7 @@ enum hdmi_infoframe_type {
 };
 
 #define HDMI_IEEE_OUI 0x000c03
+#define HDMI_FORUM_IEEE_OUI 0xc45dd8
 #define HDMI_INFOFRAME_HEADER_SIZE  4
 #define HDMI_AVI_INFOFRAME_SIZE    13
 #define HDMI_SPD_INFOFRAME_SIZE    25