drm/edid: abstract cea data block collection size

Add a function to get the cea data block collection size.

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/5339ab3249400a3c41001967e7ff2611b58e0425.1654674560.git.jani.nikula@intel.com

drivers/gpu/drm/drm_edid.c

@@ -4482,6 +4482,20 @@ __cea_db_iter_current_block(const struct cea_db_iter *iter)
 	return NULL;
 }
 
+/*
+ * References:
+ * - CTA-861-H section 7.3.3 CTA Extension Version 3
+ */
+static int cea_db_collection_size(const u8 *cta)
+{
+	u8 d = cta[2];
+
+	if (d < 4 || d > 127)
+		return 0;
+
+	return d - 4;
+}
+
 /*
  * References:
  * - VESA E-EDID v1.4
@@ -4492,15 +4506,19 @@ static const void *__cea_db_iter_edid_next(struct cea_db_iter *iter)
 	const u8 *ext;
 
 	drm_edid_iter_for_each(ext, &iter->edid_iter) {
+		int size;
+
 		/* Only support CTA Extension revision 3+ */
 		if (ext[0] != CEA_EXT || cea_revision(ext) < 3)
 			continue;
 
-		iter->index = 4;
-		iter->end = ext[2];
-		if (iter->end < 4 || iter->end > 127)
+		size = cea_db_collection_size(ext);
+		if (!size)
 			continue;
 
+		iter->index = 4;
+		iter->end = iter->index + size;
+
 		return ext;
 	}