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, 33 insertions, 4 deletions

diff --git a/drivers/net/dsa/microchip/ksz_common.c b/drivers/net/dsa/microchip/ksz_common.c
index f492fa9f6dd4..f424b3d10781 100644
--- a/drivers/net/dsa/microchip/ksz_common.c
+++ b/drivers/net/dsa/microchip/ksz_common.c
@@ -2,7 +2,7 @@
 /*
  * Microchip switch driver main logic
  *
- * Copyright (C) 2017-2024 Microchip Technology Inc.
+ * Copyright (C) 2017-2025 Microchip Technology Inc.
  */
 
 #include <linux/delay.h>
@@ -408,12 +408,29 @@ static void ksz9477_phylink_mac_link_up(struct phylink_config *config,
 					int speed, int duplex, bool tx_pause,
 					bool rx_pause);
 
+static struct phylink_pcs *
+ksz_phylink_mac_select_pcs(struct phylink_config *config,
+			   phy_interface_t interface)
+{
+	struct dsa_port *dp = dsa_phylink_to_port(config);
+	struct ksz_device *dev = dp->ds->priv;
+	struct ksz_port *p = &dev->ports[dp->index];
+
+	if (ksz_is_sgmii_port(dev, dp->index) &&
+	    (interface == PHY_INTERFACE_MODE_SGMII ||
+	    interface == PHY_INTERFACE_MODE_1000BASEX))
+		return p->pcs;
+
+	return NULL;
+}
+
 static const struct phylink_mac_ops ksz9477_phylink_mac_ops = {
 	.mac_config	= ksz_phylink_mac_config,
 	.mac_link_down	= ksz_phylink_mac_link_down,
 	.mac_link_up	= ksz9477_phylink_mac_link_up,
 	.mac_disable_tx_lpi = ksz_phylink_mac_disable_tx_lpi,
 	.mac_enable_tx_lpi = ksz_phylink_mac_enable_tx_lpi,
+	.mac_select_pcs	= ksz_phylink_mac_select_pcs,
 };
 
 static const struct ksz_dev_ops ksz9477_dev_ops = {
@@ -451,6 +468,7 @@ static const struct ksz_dev_ops ksz9477_dev_ops = {
 	.reset = ksz9477_reset_switch,
 	.init = ksz9477_switch_init,
 	.exit = ksz9477_switch_exit,
+	.pcs_create = ksz9477_pcs_create,
 };
 
 static const struct phylink_mac_ops lan937x_phylink_mac_ops = {
@@ -1093,8 +1111,7 @@ static const struct regmap_range ksz9477_valid_regs[] = {
 	regmap_reg_range(0x701b, 0x701b),
 	regmap_reg_range(0x701f, 0x7020),
 	regmap_reg_range(0x7030, 0x7030),
-	regmap_reg_range(0x7200, 0x7203),
-	regmap_reg_range(0x7206, 0x7207),
+	regmap_reg_range(0x7200, 0x7207),
 	regmap_reg_range(0x7300, 0x7301),
 	regmap_reg_range(0x7400, 0x7401),
 	regmap_reg_range(0x7403, 0x7403),
@@ -1610,6 +1627,7 @@ const struct ksz_chip_data ksz_switch_chips[] = {
 				   true, false, false},
 		.gbit_capable	= {true, true, true, true, true, true, true},
 		.ptp_capable = true,
+		.sgmii_port = 7,
 		.wr_table = &ksz9477_register_set,
 		.rd_table = &ksz9477_register_set,
 	},
@@ -2002,6 +2020,7 @@ const struct ksz_chip_data ksz_switch_chips[] = {
 		.internal_phy	= {true, true, true, true,
 				   true, false, false},
 		.gbit_capable	= {true, true, true, true, true, true, true},
+		.sgmii_port = 7,
 		.wr_table = &ksz9477_register_set,
 		.rd_table = &ksz9477_register_set,
 	},
@@ -2137,7 +2156,7 @@ void ksz_r_mib_stats64(struct ksz_device *dev, int port)
 
 	spin_unlock(&mib->stats64_lock);
 
-	if (dev->info->phy_errata_9477) {
+	if (dev->info->phy_errata_9477 && !ksz_is_sgmii_port(dev, port)) {
 		ret = ksz9477_errata_monitor(dev, port, raw->tx_late_col);
 		if (ret)
 			dev_err(dev->dev, "Failed to monitor transmission halt\n");
@@ -2845,6 +2864,12 @@ static int ksz_setup(struct dsa_switch *ds)
 	if (ret)
 		return ret;
 
+	if (ksz_has_sgmii_port(dev) && dev->dev_ops->pcs_create) {
+		ret = dev->dev_ops->pcs_create(dev);
+		if (ret)
+			return ret;
+	}
+
 	/* set broadcast storm protection 10% rate */
 	regmap_update_bits(ksz_regmap_16(dev), regs[S_BROADCAST_CTRL],
 			   BROADCAST_STORM_RATE,
@@ -3692,6 +3717,10 @@ static void ksz_phylink_mac_config(struct phylink_config *config,
 	if (dev->info->internal_phy[port])
 		return;
 
+	/* No need to configure XMII control register when using SGMII. */
+	if (ksz_is_sgmii_port(dev, port))
+		return;
+
 	if (phylink_autoneg_inband(mode)) {
 		dev_err(dev->dev, "In-band AN not supported!\n");
 		return;