drm: rcar-du: Recognize "renesas,vsps" in addition to "vsps"

The Renesas-specific "vsps" property lacks a vendor prefix.
Add a "renesas," prefix to comply with DT best practises.
Retain backward compatibility with old DTBs by falling back to "vsps"
when needed.

Fixes: 6d62ef3 ("drm: rcar-du: Expose the VSP1 compositor through KMS planes")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>

drivers/gpu/drm/rcar-du/rcar_du_kms.c

@@ -544,6 +544,7 @@ static int rcar_du_properties_init(struct rcar_du_device *rcdu)
 static int rcar_du_vsps_init(struct rcar_du_device *rcdu)
 {
 	const struct device_node *np = rcdu->dev->of_node;
+	const char *vsps_prop_name = "renesas,vsps";
 	struct of_phandle_args args;
 	struct {
 		struct device_node *np;
@@ -559,15 +560,21 @@ static int rcar_du_vsps_init(struct rcar_du_device *rcdu)
 	 * entry contains a pointer to the VSP DT node and a bitmask of the
 	 * connected DU CRTCs.
 	 */
-	cells = of_property_count_u32_elems(np, "vsps") / rcdu->num_crtcs - 1;
+	ret = of_property_count_u32_elems(np, vsps_prop_name);
+	if (ret < 0) {
+		/* Backward compatibility with old DTBs. */
+		vsps_prop_name = "vsps";
+		ret = of_property_count_u32_elems(np, vsps_prop_name);
+	}
+	cells = ret / rcdu->num_crtcs - 1;
 	if (cells > 1)
 		return -EINVAL;
 
 	for (i = 0; i < rcdu->num_crtcs; ++i) {
 		unsigned int j;
 
-		ret = of_parse_phandle_with_fixed_args(np, "vsps", cells, i,
-						       &args);
+		ret = of_parse_phandle_with_fixed_args(np, vsps_prop_name,
+						       cells, i, &args);
 		if (ret < 0)
 			goto error;
 
@@ -589,8 +596,8 @@ static int rcar_du_vsps_init(struct rcar_du_device *rcdu)
 
 		/*
 		 * Store the VSP pointer and pipe index in the CRTC. If the
-		 * second cell of the 'vsps' specifier isn't present, default
-		 * to 0 to remain compatible with older DT bindings.
+		 * second cell of the 'renesas,vsps' specifier isn't present,
+		 * default to 0 to remain compatible with older DT bindings.
 		 */
 		rcdu->crtcs[i].vsp = &rcdu->vsps[j];
 		rcdu->crtcs[i].vsp_pipe = cells >= 1 ? args.args[0] : 0;