edid: Add an edid_check_checksum() helper function

Add a helper function to check the checksum of an EDID data block.
Signed-off-by: NHans de Goede <hdegoede@redhat.com>
Acked-by: NAnatolij Gustschin <agust@denx.de>

common/edid.c

@@ -12,6 +12,7 @@
 
 #include <common.h>
 #include <edid.h>
+#include <errno.h>
 #include <linux/ctype.h>
 #include <linux/string.h>
 
@@ -29,6 +30,17 @@ int edid_check_info(struct edid1_info *edid_info)
 	return 0;
 }
 
+int edid_check_checksum(u8 *edid_block)
+{
+	u8 checksum = 0;
+	int i;
+
+	for (i = 0; i < 128; i++)
+		checksum += edid_block[i];
+
+	return (checksum == 0) ? 0 : -EINVAL;
+}
+
 int edid_get_ranges(struct edid1_info *edid, unsigned int *hmin,
 		    unsigned int *hmax, unsigned int *vmin,
 		    unsigned int *vmax)

include/edid.h

@@ -245,6 +245,15 @@ void edid_print_info(struct edid1_info *edid_info);
  */
 int edid_check_info(struct edid1_info *info);
 
+/**
+ * Check checksum of a 128 bytes EDID data block
+ *
+ * @param edid_block	EDID block data
+ *
+ * @return 0 on success, or a negative errno on error
+ */
+int edid_check_checksum(u8 *edid_block);
+
 /**
  * Get the horizontal and vertical rate ranges of the monitor.
  *