net: dsa: rtl8366rb: Support setting STP state

This adds support for setting the STP state to the RTL8366RB
DSA switch. This rids the following message from the kernel on
e.g. OpenWrt:

DSA: failed to set STP state 3 (-95)

Since the RTL8366RB has one STP state register per FID with
two bit per port in each, we simply loop over all the FIDs
and set the state on all of them.

Cc: Vladimir Oltean <olteanv@gmail.com>
Cc: Alvin Šipraga <alsi@bang-olufsen.dk>
Cc: Mauri Sandberg <sandberg@mailfence.com>
Cc: DENG Qingfang <dqfext@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/rtl8366rb.c

@@ -110,6 +110,18 @@
 
 #define RTL8366RB_POWER_SAVING_REG	0x0021
 
+/* Spanning tree status (STP) control, two bits per port per FID */
+#define RTL8366RB_STP_STATE_BASE	0x0050 /* 0x0050..0x0057 */
+#define RTL8366RB_STP_STATE_DISABLED	0x0
+#define RTL8366RB_STP_STATE_BLOCKING	0x1
+#define RTL8366RB_STP_STATE_LEARNING	0x2
+#define RTL8366RB_STP_STATE_FORWARDING	0x3
+#define RTL8366RB_STP_MASK		GENMASK(1, 0)
+#define RTL8366RB_STP_STATE(port, state) \
+	((state) << ((port) * 2))
+#define RTL8366RB_STP_STATE_MASK(port) \
+	RTL8366RB_STP_STATE((port), RTL8366RB_STP_MASK)
+
 /* CPU port control reg */
 #define RTL8368RB_CPU_CTRL_REG		0x0061
 #define RTL8368RB_CPU_PORTS_MSK		0x00FF
@@ -234,6 +246,7 @@
 #define RTL8366RB_NUM_LEDGROUPS		4
 #define RTL8366RB_NUM_VIDS		4096
 #define RTL8366RB_PRIORITYMAX		7
+#define RTL8366RB_NUM_FIDS		8
 #define RTL8366RB_FIDMAX		7
 
 #define RTL8366RB_PORT_1		BIT(0) /* In userspace port 0 */
@@ -1308,6 +1321,40 @@ rtl8366rb_port_bridge_flags(struct dsa_switch *ds, int port,
 	return 0;
 }
 
+static void
+rtl8366rb_port_stp_state_set(struct dsa_switch *ds, int port, u8 state)
+{
+	struct realtek_smi *smi = ds->priv;
+	u32 val;
+	int i;
+
+	switch (state) {
+	case BR_STATE_DISABLED:
+		val = RTL8366RB_STP_STATE_DISABLED;
+		break;
+	case BR_STATE_BLOCKING:
+	case BR_STATE_LISTENING:
+		val = RTL8366RB_STP_STATE_BLOCKING;
+		break;
+	case BR_STATE_LEARNING:
+		val = RTL8366RB_STP_STATE_LEARNING;
+		break;
+	case BR_STATE_FORWARDING:
+		val = RTL8366RB_STP_STATE_FORWARDING;
+		break;
+	default:
+		dev_err(smi->dev, "unknown bridge state requested\n");
+		return;
+	};
+
+	/* Set the same status for the port on all the FIDs */
+	for (i = 0; i < RTL8366RB_NUM_FIDS; i++) {
+		regmap_update_bits(smi->map, RTL8366RB_STP_STATE_BASE + i,
+				   RTL8366RB_STP_STATE_MASK(port),
+				   RTL8366RB_STP_STATE(port, val));
+	}
+}
+
 static void
 rtl8366rb_port_fast_age(struct dsa_switch *ds, int port)
 {
@@ -1733,6 +1780,7 @@ static const struct dsa_switch_ops rtl8366rb_switch_ops = {
 	.port_disable = rtl8366rb_port_disable,
 	.port_pre_bridge_flags = rtl8366rb_port_pre_bridge_flags,
 	.port_bridge_flags = rtl8366rb_port_bridge_flags,
+	.port_stp_state_set = rtl8366rb_port_stp_state_set,
 	.port_fast_age = rtl8366rb_port_fast_age,
 	.port_change_mtu = rtl8366rb_change_mtu,
 	.port_max_mtu = rtl8366rb_max_mtu,