--- zzzz-none-000/linux-5.4.213/drivers/net/dsa/rtl8366rb.c	2022-09-15 10:04:56.000000000 +0000
+++ alder-5690pro-762/linux-5.4.213/drivers/net/dsa/rtl8366rb.c	2024-08-14 09:02:07.000000000 +0000
@@ -109,8 +109,8 @@
 /* CPU port control reg */
 #define RTL8368RB_CPU_CTRL_REG		0x0061
 #define RTL8368RB_CPU_PORTS_MSK		0x00FF
-/* Enables inserting custom tag length/type 0x8899 */
-#define RTL8368RB_CPU_INSTAG		BIT(15)
+/* Disables inserting custom tag length/type 0x8899 */
+#define RTL8368RB_CPU_NO_TAG		BIT(15)
 
 #define RTL8366RB_SMAR0			0x0070 /* bits 0..15 */
 #define RTL8366RB_SMAR1			0x0071 /* bits 16..31 */
@@ -844,16 +844,14 @@
 	if (ret)
 		return ret;
 
-	/* Enable CPU port and enable inserting CPU tag
+	/* Enable CPU port with custom DSA tag 8899.
 	 *
-	 * Disabling RTL8368RB_CPU_INSTAG here will change the behaviour
-	 * of the switch totally and it will start talking Realtek RRCP
-	 * internally. It is probably possible to experiment with this,
-	 * but then the kernel needs to understand and handle RRCP first.
+	 * If you set RTL8368RB_CPU_NO_TAG (bit 15) in this registers
+	 * the custom tag is turned off.
 	 */
 	ret = regmap_update_bits(smi->map, RTL8368RB_CPU_CTRL_REG,
 				 0xFFFF,
-				 RTL8368RB_CPU_INSTAG | BIT(smi->cpu_port));
+				 BIT(smi->cpu_port));
 	if (ret)
 		return ret;
 
@@ -966,21 +964,8 @@
 static enum dsa_tag_protocol rtl8366_get_tag_protocol(struct dsa_switch *ds,
 						      int port)
 {
-	/* For now, the RTL switches are handled without any custom tags.
-	 *
-	 * It is possible to turn on "custom tags" by removing the
-	 * RTL8368RB_CPU_INSTAG flag when enabling the port but what it
-	 * does is unfamiliar to DSA: ethernet frames of type 8899, the Realtek
-	 * Remote Control Protocol (RRCP) start to appear on the CPU port of
-	 * the device. So this is not the ordinary few extra bytes in the
-	 * frame. Instead it appears that the switch starts to talk Realtek
-	 * RRCP internally which means a pretty complex RRCP implementation
-	 * decoding and responding the RRCP protocol is needed to exploit this.
-	 *
-	 * The OpenRRCP project (dormant since 2009) have reverse-egineered
-	 * parts of the protocol.
-	 */
-	return DSA_TAG_PROTO_NONE;
+	/* This switch uses the 4 byte protocol A Realtek DSA tag */
+	return DSA_TAG_PROTO_RTL4_A;
 }
 
 static void rtl8366rb_adjust_link(struct dsa_switch *ds, int port,