net: dsa: rtl8366rb: Roof MTU for switch

The MTU setting for this DSA switch is global so we need
to keep track of the MTU set for each port, then as soon
as any MTU changes, roof the MTU to the biggest common
denominator and poke that into the switch MTU setting.

To achieve this we need a per-chip-variant state container
for the RTL8366RB to use for the RTL8366RB-specific
stuff. Other SMI switches does seem to have per-port
MTU setting capabilities.

Fixes: 5f4a8ef ("net: dsa: rtl8366rb: Support setting MTU")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/net/dsa/realtek-smi-core.c

@@ -394,9 +394,10 @@ static int realtek_smi_probe(struct platform_device *pdev)
 	var = of_device_get_match_data(dev);
 	np = dev->of_node;
 
-	smi = devm_kzalloc(dev, sizeof(*smi), GFP_KERNEL);
+	smi = devm_kzalloc(dev, sizeof(*smi) + var->chip_data_sz, GFP_KERNEL);
 	if (!smi)
 		return -ENOMEM;
+	smi->chip_data = (void *)smi + sizeof(*smi);
 	smi->map = devm_regmap_init(dev, NULL, smi,
 				    &realtek_smi_mdio_regmap_config);
 	if (IS_ERR(smi->map)) {

drivers/net/dsa/realtek-smi-core.h

@@ -71,6 +71,7 @@ struct realtek_smi {
 	int			vlan4k_enabled;
 
 	char			buf[4096];
+	void			*chip_data; /* Per-chip extra variant data */
 };
 
 /**
@@ -111,6 +112,7 @@ struct realtek_smi_variant {
 	unsigned int clk_delay;
 	u8 cmd_read;
 	u8 cmd_write;
+	size_t chip_data_sz;
 };
 
 /* SMI core calls */

drivers/net/dsa/rtl8366rb.c

@@ -311,6 +311,13 @@
 #define RTL8366RB_GREEN_FEATURE_TX	BIT(0)
 #define RTL8366RB_GREEN_FEATURE_RX	BIT(2)
 
+/**
+ * struct rtl8366rb - RTL8366RB-specific data
+ */
+struct rtl8366rb {
+	unsigned int max_mtu[RTL8366RB_NUM_PORTS];
+};
+
 static struct rtl8366_mib_counter rtl8366rb_mib_counters[] = {
 	{ 0,  0, 4, "IfInOctets"				},
 	{ 0,  4, 4, "EtherStatsOctets"				},
@@ -710,6 +717,7 @@ static const u16 rtl8366rb_green_jam[][2] = {
 
 static int rtl8366rb_setup(struct dsa_switch *ds)
 {
+	struct rtl8366rb *rb = smi->chip_data;
 	struct realtek_smi *smi = ds->priv;
 	const u16 *jam_table;
 	u32 chip_ver = 0;
@@ -868,6 +876,9 @@ static int rtl8366rb_setup(struct dsa_switch *ds)
 				 RTL8366RB_SGCR_MAX_LENGTH_1536);
 	if (ret)
 		return ret;
+	for (i = 0; i < RTL8366RB_NUM_PORTS; i++)
+		/* layer 2 size, see rtl8366rb_change_mtu() */
+		rb->max_mtu[i] = 1532;
 
 	/* Enable learning for all ports */
 	ret = regmap_write(smi->map, RTL8366RB_SSCR0, 0);
@@ -1109,20 +1120,36 @@ rtl8366rb_port_disable(struct dsa_switch *ds, int port)
 static int rtl8366rb_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
 {
 	struct realtek_smi *smi = ds->priv;
+	struct rtl8366rb *rb;
+	unsigned int max_mtu;
 	u32 len;
+	int i;
 
-	/* The first setting, 1522 bytes, is max IP packet 1500 bytes,
+	/* Cache the per-port MTU setting */
+	rb = smi->chip_data;
+	rb->max_mtu[port] = new_mtu;
+
+	/* Roof out the MTU for the entire switch to the greatest
+	 * common denominator: the biggest set for any one port will
+	 * be the biggest MTU for the switch.
+	 *
+	 * The first setting, 1522 bytes, is max IP packet 1500 bytes,
 	 * plus ethernet header, 1518 bytes, plus CPU tag, 4 bytes.
 	 * This function should consider the parameter an SDU, so the
 	 * MTU passed for this setting is 1518 bytes. The same logic
 	 * of subtracting the DSA tag of 4 bytes apply to the other
 	 * settings.
 	 */
-	if (new_mtu <= 1518)
+	max_mtu = 1518;
+	for (i = 0; i < RTL8366RB_NUM_PORTS; i++) {
+		if (rb->max_mtu[i] > max_mtu)
+			max_mtu = rb->max_mtu[i];
+	}
+	if (max_mtu <= 1518)
 		len = RTL8366RB_SGCR_MAX_LENGTH_1522;
-	else if (new_mtu > 1518 && new_mtu <= 1532)
+	else if (max_mtu > 1518 && max_mtu <= 1532)
 		len = RTL8366RB_SGCR_MAX_LENGTH_1536;
-	else if (new_mtu > 1532 && new_mtu <= 1548)
+	else if (max_mtu > 1532 && max_mtu <= 1548)
 		len = RTL8366RB_SGCR_MAX_LENGTH_1552;
 	else
 		len = RTL8366RB_SGCR_MAX_LENGTH_16000;
@@ -1505,5 +1532,6 @@ const struct realtek_smi_variant rtl8366rb_variant = {
 	.clk_delay = 10,
 	.cmd_read = 0xa9,
 	.cmd_write = 0xa8,
+	.chip_data_sz = sizeof(struct rtl8366rb),
 };
 EXPORT_SYMBOL_GPL(rtl8366rb_variant);