net: dsa: microchip: Add SGMII port support to KSZ9477 switch

The KSZ9477 switch driver uses the XPCS driver to operate its SGMII
port.  However there are some hardware bugs in the KSZ9477 SGMII
module so workarounds are needed.  There was a proposal to update the
XPCS driver to accommodate KSZ9477, but the new code is not generic
enough to be used by other vendors.  It is better to do all these
workarounds inside the KSZ9477 driver instead of modifying the XPCS
driver.

There are 3 hardware issues.  The first is the MII_ADVERTISE register
needs to be write once after reset for the correct code word to be
sent.  The XPCS driver disables auto-negotiation first before
configuring the SGMII/1000BASE-X mode and then enables it back.  The
KSZ9477 driver then writes the MII_ADVERTISE register before enabling
auto-negotiation.  In 1000BASE-X mode the MII_ADVERTISE register will
be set, so KSZ9477 driver does not need to write it.

The second issue is the MII_BMCR register needs to set the exact speed
and duplex mode when running in SGMII mode.  During link polling the
KSZ9477 will check the speed and duplex mode are different from
previous ones and update the MII_BMCR register accordingly.

The last issue is 1000BASE-X mode does not work with auto-negotiation
on.  The cause is the local port hardware does not know the link is up
and so network traffic is not forwarded.  The workaround is to write 2
additional bits when 1000BASE-X mode is configured.

Note the SGMII interrupt in the port cannot be masked.  As that
interrupt is not handled in the KSZ9477 driver the SGMII interrupt bit
will not be set even when the XPCS driver sets it.

Signed-off-by: Tristram Ha <tristram.ha@microchip.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20250520230720.23425-1-Tristram.Ha@microchip.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

1 files changed, 193 insertions, 1 deletions

diff --git a/drivers/net/dsa/microchip/ksz9477.c b/drivers/net/dsa/microchip/ksz9477.c
index 29fe79ea74cd..d747ea1c41a7 100644
--- a/drivers/net/dsa/microchip/ksz9477.c
+++ b/drivers/net/dsa/microchip/ksz9477.c
@@ -2,7 +2,7 @@
 /*
  * Microchip KSZ9477 switch driver main logic
  *
- * Copyright (C) 2017-2024 Microchip Technology Inc.
+ * Copyright (C) 2017-2025 Microchip Technology Inc.
  */
 
 #include <linux/kernel.h>
@@ -161,6 +161,190 @@ static int ksz9477_wait_alu_sta_ready(struct ksz_device *dev)
 					10, 1000);
 }
 
+static void port_sgmii_s(struct ksz_device *dev, uint port, u16 devid, u16 reg)
+{
+	u32 data;
+
+	data = (devid & MII_MMD_CTRL_DEVAD_MASK) << 16;
+	data |= reg;
+	ksz_pwrite32(dev, port, REG_PORT_SGMII_ADDR__4, data);
+}
+
+static void port_sgmii_r(struct ksz_device *dev, uint port, u16 devid, u16 reg,
+			 u16 *buf)
+{
+	port_sgmii_s(dev, port, devid, reg);
+	ksz_pread16(dev, port, REG_PORT_SGMII_DATA__4 + 2, buf);
+}
+
+static void port_sgmii_w(struct ksz_device *dev, uint port, u16 devid, u16 reg,
+			 u16 buf)
+{
+	port_sgmii_s(dev, port, devid, reg);
+	ksz_pwrite32(dev, port, REG_PORT_SGMII_DATA__4, buf);
+}
+
+static int ksz9477_pcs_read(struct mii_bus *bus, int phy, int mmd, int reg)
+{
+	struct ksz_device *dev = bus->priv;
+	int port = ksz_get_sgmii_port(dev);
+	u16 val;
+
+	port_sgmii_r(dev, port, mmd, reg, &val);
+
+	/* Simulate a value to activate special code in the XPCS driver if
+	 * supported.
+	 */
+	if (mmd == MDIO_MMD_PMAPMD) {
+		if (reg == MDIO_DEVID1)
+			val = 0x9477;
+		else if (reg == MDIO_DEVID2)
+			val = 0x22 << 10;
+	} else if (mmd == MDIO_MMD_VEND2) {
+		struct ksz_port *p = &dev->ports[port];
+
+		/* Need to update MII_BMCR register with the exact speed and
+		 * duplex mode when running in SGMII mode and this register is
+		 * used to detect connected speed in that mode.
+		 */
+		if (reg == MMD_SR_MII_AUTO_NEG_STATUS) {
+			int duplex, speed;
+
+			if (val & SR_MII_STAT_LINK_UP) {
+				speed = (val >> SR_MII_STAT_S) & SR_MII_STAT_M;
+				if (speed == SR_MII_STAT_1000_MBPS)
+					speed = SPEED_1000;
+				else if (speed == SR_MII_STAT_100_MBPS)
+					speed = SPEED_100;
+				else
+					speed = SPEED_10;
+
+				if (val & SR_MII_STAT_FULL_DUPLEX)
+					duplex = DUPLEX_FULL;
+				else
+					duplex = DUPLEX_HALF;
+
+				if (!p->phydev.link ||
+				    p->phydev.speed != speed ||
+				    p->phydev.duplex != duplex) {
+					u16 ctrl;
+
+					p->phydev.link = 1;
+					p->phydev.speed = speed;
+					p->phydev.duplex = duplex;
+					port_sgmii_r(dev, port, mmd, MII_BMCR,
+						     &ctrl);
+					ctrl &= BMCR_ANENABLE;
+					ctrl |= mii_bmcr_encode_fixed(speed,
+								      duplex);
+					port_sgmii_w(dev, port, mmd, MII_BMCR,
+						     ctrl);
+				}
+			} else {
+				p->phydev.link = 0;
+			}
+		} else if (reg == MII_BMSR) {
+			p->phydev.link = (val & BMSR_LSTATUS);
+		}
+	}
+
+	return val;
+}
+
+static int ksz9477_pcs_write(struct mii_bus *bus, int phy, int mmd, int reg,
+			     u16 val)
+{
+	struct ksz_device *dev = bus->priv;
+	int port = ksz_get_sgmii_port(dev);
+
+	if (mmd == MDIO_MMD_VEND2) {
+		struct ksz_port *p = &dev->ports[port];
+
+		if (reg == MMD_SR_MII_AUTO_NEG_CTRL) {
+			u16 sgmii_mode = SR_MII_PCS_SGMII << SR_MII_PCS_MODE_S;
+
+			/* Need these bits for 1000BASE-X mode to work with
+			 * AN on.
+			 */
+			if (!(val & sgmii_mode))
+				val |= SR_MII_SGMII_LINK_UP |
+				       SR_MII_TX_CFG_PHY_MASTER;
+
+			/* SGMII interrupt in the port cannot be masked, so
+			 * make sure interrupt is not enabled as it is not
+			 * handled.
+			 */
+			val &= ~SR_MII_AUTO_NEG_COMPLETE_INTR;
+		} else if (reg == MII_BMCR) {
+			/* The MII_ADVERTISE register needs to write once
+			 * before doing auto-negotiation for the correct
+			 * config_word to be sent out after reset.
+			 */
+			if ((val & BMCR_ANENABLE) && !p->sgmii_adv_write) {
+				u16 adv;
+
+				/* The SGMII port cannot disable flow control
+				 * so it is better to just advertise symmetric
+				 * pause.
+				 */
+				port_sgmii_r(dev, port, mmd, MII_ADVERTISE,
+					     &adv);
+				adv |= ADVERTISE_1000XPAUSE;
+				adv &= ~ADVERTISE_1000XPSE_ASYM;
+				port_sgmii_w(dev, port, mmd, MII_ADVERTISE,
+					     adv);
+				p->sgmii_adv_write = 1;
+			} else if (val & BMCR_RESET) {
+				p->sgmii_adv_write = 0;
+			}
+		} else if (reg == MII_ADVERTISE) {
+			/* XPCS driver writes to this register so there is no
+			 * need to update it for the errata.
+			 */
+			p->sgmii_adv_write = 1;
+		}
+	}
+	port_sgmii_w(dev, port, mmd, reg, val);
+
+	return 0;
+}
+
+int ksz9477_pcs_create(struct ksz_device *dev)
+{
+	/* This chip has a SGMII port. */
+	if (ksz_has_sgmii_port(dev)) {
+		int port = ksz_get_sgmii_port(dev);
+		struct ksz_port *p = &dev->ports[port];
+		struct phylink_pcs *pcs;
+		struct mii_bus *bus;
+		int ret;
+
+		bus = devm_mdiobus_alloc(dev->dev);
+		if (!bus)
+			return -ENOMEM;
+
+		bus->name = "ksz_pcs_mdio_bus";
+		snprintf(bus->id, MII_BUS_ID_SIZE, "%s-pcs",
+			 dev_name(dev->dev));
+		bus->read_c45 = &ksz9477_pcs_read;
+		bus->write_c45 = &ksz9477_pcs_write;
+		bus->parent = dev->dev;
+		bus->phy_mask = ~0;
+		bus->priv = dev;
+
+		ret = devm_mdiobus_register(dev->dev, bus);
+		if (ret)
+			return ret;
+
+		pcs = xpcs_create_pcs_mdiodev(bus, 0);
+		if (IS_ERR(pcs))
+			return PTR_ERR(pcs);
+		p->pcs = pcs;
+	}
+
+	return 0;
+}
+
 int ksz9477_reset_switch(struct ksz_device *dev)
 {
 	u8 data8;
@@ -978,6 +1162,14 @@ void ksz9477_get_caps(struct ksz_device *dev, int port,
 
 	if (dev->info->gbit_capable[port])
 		config->mac_capabilities |= MAC_1000FD;
+
+	if (ksz_is_sgmii_port(dev, port)) {
+		struct ksz_port *p = &dev->ports[port];
+
+		phy_interface_or(config->supported_interfaces,
+				 config->supported_interfaces,
+				 p->pcs->supported_interfaces);
+	}
 }
 
 int ksz9477_set_ageing_time(struct ksz_device *dev, unsigned int msecs)