drm/edid: clean up EDID block checksum functions

Have two clear functions, one to compute the checksum over the EDID, and
another to get the checksum from the EDID. Throw away the diff function.

Ditch the drm_ prefix for static functions, and accept const void * to
help transition to struct edid * usage.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/36641401c8eb0e403c0e33365ff4ad9a28f9fd4a.1648752228.git.jani.nikula@intel.com

drivers/gpu/drm/drm_edid.c

@@ -1597,25 +1597,25 @@ module_param_named(edid_fixup, edid_fixup, int, 0400);
 MODULE_PARM_DESC(edid_fixup,
 		 "Minimum number of valid EDID header bytes (0-8, default 6)");
 
-static int drm_edid_block_checksum(const u8 *raw_edid)
+static int edid_block_compute_checksum(const void *_block)
 {
+	const u8 *block = _block;
 	int i;
 	u8 csum = 0, crc = 0;
 
 	for (i = 0; i < EDID_LENGTH - 1; i++)
-		csum += raw_edid[i];
+		csum += block[i];
 
 	crc = 0x100 - csum;
 
 	return crc;
 }
 
-static bool drm_edid_block_checksum_diff(const u8 *raw_edid, u8 real_checksum)
+static int edid_block_get_checksum(const void *_block)
 {
-	if (raw_edid[EDID_LENGTH - 1] != real_checksum)
-		return true;
-	else
-		return false;
+	const struct edid *block = _block;
+
+	return block->checksum;
 }
 
 static bool drm_edid_is_zero(const u8 *in_edid, int length)
@@ -1704,8 +1704,8 @@ bool drm_edid_block_valid(u8 *raw_edid, int block, bool print_bad_edid,
 		}
 	}
 
-	csum = drm_edid_block_checksum(raw_edid);
-	if (drm_edid_block_checksum_diff(raw_edid, csum)) {
+	csum = edid_block_compute_checksum(raw_edid);
+	if (csum != edid_block_get_checksum(raw_edid)) {
 		if (edid_corrupt)
 			*edid_corrupt = true;
 
@@ -1859,7 +1859,7 @@ static void connector_bad_edid(struct drm_connector *connector,
 	/* Calculate real checksum for the last edid extension block data */
 	if (last_block < num_blocks)
 		connector->real_edid_checksum =
-			drm_edid_block_checksum(edid + last_block * EDID_LENGTH);
+			edid_block_compute_checksum(edid + last_block * EDID_LENGTH);
 
 	if (connector->bad_edid_counter++ && !drm_debug_enabled(DRM_UT_KMS))
 		return;