net: dsa: microchip: ksz8: add MTU configuration support

Make MTU configurable on KSZ87xx and KSZ88xx series of switches.

Before this patch, pre-configured behavior was different on different
switch series, due to opposite meaning of the same bit:
- KSZ87xx: Reg 4, Bit 1 - if 1, max frame size is 1532; if 0 - 1514
- KSZ88xx: Reg 4, Bit 1 - if 1, max frame size is 1514; if 0 - 1532

Since the code was telling "... SW_LEGAL_PACKET_DISABLE, true)", I
assume, the idea was to set max frame size to 1532.

With this patch, by setting MTU size 1500, both switch series will be
configured to the 1532 frame limit.

This patch was tested on KSZ8873.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Vladimir Oltean <olteanv@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

drivers/net/dsa/microchip/ksz8.h

@@ -57,5 +57,6 @@ int ksz8_reset_switch(struct ksz_device *dev);
 int ksz8_switch_detect(struct ksz_device *dev);
 int ksz8_switch_init(struct ksz_device *dev);
 void ksz8_switch_exit(struct ksz_device *dev);
+int ksz8_change_mtu(struct ksz_device *dev, int port, int mtu);
 
 #endif

drivers/net/dsa/microchip/ksz8795.c

@@ -76,6 +76,57 @@ int ksz8_reset_switch(struct ksz_device *dev)
 	return 0;
 }
 
+static int ksz8863_change_mtu(struct ksz_device *dev, int frame_size)
+{
+	u8 ctrl2 = 0;
+
+	if (frame_size <= KSZ8_LEGAL_PACKET_SIZE)
+		ctrl2 |= KSZ8863_LEGAL_PACKET_ENABLE;
+	else if (frame_size > KSZ8863_NORMAL_PACKET_SIZE)
+		ctrl2 |= KSZ8863_HUGE_PACKET_ENABLE;
+
+	return ksz_rmw8(dev, REG_SW_CTRL_2, KSZ8863_LEGAL_PACKET_ENABLE |
+			KSZ8863_HUGE_PACKET_ENABLE, ctrl2);
+}
+
+static int ksz8795_change_mtu(struct ksz_device *dev, int frame_size)
+{
+	u8 ctrl1 = 0, ctrl2 = 0;
+	int ret;
+
+	if (frame_size > KSZ8_LEGAL_PACKET_SIZE)
+		ctrl2 |= SW_LEGAL_PACKET_DISABLE;
+	else if (frame_size > KSZ8863_NORMAL_PACKET_SIZE)
+		ctrl1 |= SW_HUGE_PACKET;
+
+	ret = ksz_rmw8(dev, REG_SW_CTRL_1, SW_HUGE_PACKET, ctrl1);
+	if (ret)
+		return ret;
+
+	return ksz_rmw8(dev, REG_SW_CTRL_2, SW_LEGAL_PACKET_DISABLE, ctrl2);
+}
+
+int ksz8_change_mtu(struct ksz_device *dev, int port, int mtu)
+{
+	u16 frame_size;
+
+	if (!dsa_is_cpu_port(dev->ds, port))
+		return 0;
+
+	frame_size = mtu + VLAN_ETH_HLEN + ETH_FCS_LEN;
+
+	switch (dev->chip_id) {
+	case KSZ8795_CHIP_ID:
+	case KSZ8794_CHIP_ID:
+	case KSZ8765_CHIP_ID:
+		return ksz8795_change_mtu(dev, frame_size);
+	case KSZ8830_CHIP_ID:
+		return ksz8863_change_mtu(dev, frame_size);
+	}
+
+	return -EOPNOTSUPP;
+}
+
 static void ksz8795_set_prio_queue(struct ksz_device *dev, int port, int queue)
 {
 	u8 hi, lo;
@@ -1233,8 +1284,6 @@ void ksz8_config_cpu_port(struct dsa_switch *ds)
 	masks = dev->info->masks;
 	regs = dev->info->regs;
 
-	/* Switch marks the maximum frame with extra byte as oversize. */
-	ksz_cfg(dev, REG_SW_CTRL_2, SW_LEGAL_PACKET_DISABLE, true);
 	ksz_cfg(dev, regs[S_TAIL_TAG_CTRL], masks[SW_TAIL_TAG_ENABLE], true);
 
 	p = &dev->ports[dev->cpu_port];

drivers/net/dsa/microchip/ksz8795_reg.h

@@ -48,6 +48,9 @@
 #define NO_EXC_COLLISION_DROP		BIT(3)
 #define SW_LEGAL_PACKET_DISABLE		BIT(1)
 
+#define KSZ8863_HUGE_PACKET_ENABLE	BIT(2)
+#define KSZ8863_LEGAL_PACKET_ENABLE	BIT(1)
+
 #define REG_SW_CTRL_3			0x05
  #define WEIGHTED_FAIR_QUEUE_ENABLE	BIT(3)
 

drivers/net/dsa/microchip/ksz_common.c

@@ -172,6 +172,7 @@ static const struct ksz_dev_ops ksz8_dev_ops = {
 	.reset = ksz8_reset_switch,
 	.init = ksz8_switch_init,
 	.exit = ksz8_switch_exit,
+	.change_mtu = ksz8_change_mtu,
 };
 
 static void ksz9477_phylink_mac_link_up(struct ksz_device *dev, int port,
@@ -2500,6 +2501,12 @@ static int ksz_max_mtu(struct dsa_switch *ds, int port)
 	struct ksz_device *dev = ds->priv;
 
 	switch (dev->chip_id) {
+	case KSZ8795_CHIP_ID:
+	case KSZ8794_CHIP_ID:
+	case KSZ8765_CHIP_ID:
+		return KSZ8795_HUGE_PACKET_SIZE - VLAN_ETH_HLEN - ETH_FCS_LEN;
+	case KSZ8830_CHIP_ID:
+		return KSZ8863_HUGE_PACKET_SIZE - VLAN_ETH_HLEN - ETH_FCS_LEN;
 	case KSZ8563_CHIP_ID:
 	case KSZ9477_CHIP_ID:
 	case KSZ9563_CHIP_ID:

drivers/net/dsa/microchip/ksz_common.h

@@ -591,6 +591,10 @@ static inline int is_lan937x(struct ksz_device *dev)
 
 #define PORT_SRC_PHY_INT		1
 
+#define KSZ8795_HUGE_PACKET_SIZE	2000
+#define KSZ8863_HUGE_PACKET_SIZE	1916
+#define KSZ8863_NORMAL_PACKET_SIZE	1536
+#define KSZ8_LEGAL_PACKET_SIZE		1518
 #define KSZ9477_MAX_FRAME_SIZE		9000
 
 /* Regmap tables generation */