drm/edid: convert drm_edid_to_sad() to use cea db iter

Use the cea db iterator for short audio descriptors. We'll still stop at
the first audio data block, but not at the first CTA Extension if that
doesn't have the info.

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/237e4b1de1567903d37ce1d1bb830020b8fd6690.1651569697.git.jani.nikula@intel.com

drivers/gpu/drm/drm_edid.c

@@ -5007,40 +5007,21 @@ static void drm_edid_to_eld(struct drm_connector *connector,
  */
 int drm_edid_to_sad(const struct edid *edid, struct cea_sad **sads)
 {
+	const struct cea_db *db;
+	struct cea_db_iter iter;
 	int count = 0;
-	int i, start, end, dbl;
-	const u8 *cea;
-
-	cea = drm_find_cea_extension(edid);
-	if (!cea) {
-		DRM_DEBUG_KMS("SAD: no CEA Extension found\n");
-		return 0;
-	}
-
-	if (cea_revision(cea) < 3) {
-		DRM_DEBUG_KMS("SAD: wrong CEA revision\n");
-		return 0;
-	}
-
-	if (cea_db_offsets(cea, &start, &end)) {
-		DRM_DEBUG_KMS("SAD: invalid data block offsets\n");
-		return -EPROTO;
-	}
-
-	for_each_cea_db(cea, i, start, end) {
-		const u8 *db = &cea[i];
 
+	cea_db_iter_edid_begin(edid, &iter);
+	cea_db_iter_for_each(db, &iter) {
 		if (cea_db_tag(db) == CTA_DB_AUDIO) {
 			int j;
 
-			dbl = cea_db_payload_len(db);
-
-			count = dbl / 3; /* SAD is 3B */
+			count = cea_db_payload_len(db) / 3; /* SAD is 3B */
 			*sads = kcalloc(count, sizeof(**sads), GFP_KERNEL);
 			if (!*sads)
 				return -ENOMEM;
 			for (j = 0; j < count; j++) {
-				const u8 *sad = &db[1 + j * 3];
+				const u8 *sad = &db->data[j * 3];
 
 				(*sads)[j].format = (sad[0] & 0x78) >> 3;
 				(*sads)[j].channels = sad[0] & 0x7;
@@ -5050,6 +5031,9 @@ int drm_edid_to_sad(const struct edid *edid, struct cea_sad **sads)
 			break;
 		}
 	}
+	cea_db_iter_end(&iter);
+
+	DRM_DEBUG_KMS("Found %d Short Audio Descriptors\n", count);
 
 	return count;
 }