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, 22 insertions, 1 deletions

diff --git a/drivers/net/dsa/microchip/ksz_common.h b/drivers/net/dsa/microchip/ksz_common.h
index a034017568cd..a08417df2ca4 100644
--- a/drivers/net/dsa/microchip/ksz_common.h
+++ b/drivers/net/dsa/microchip/ksz_common.h
@@ -1,7 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 /* Microchip switch driver common header
  *
- * Copyright (C) 2017-2024 Microchip Technology Inc.
+ * Copyright (C) 2017-2025 Microchip Technology Inc.
  */
 
 #ifndef __KSZ_COMMON_H
@@ -10,6 +10,7 @@
 #include <linux/etherdevice.h>
 #include <linux/kernel.h>
 #include <linux/mutex.h>
+#include <linux/pcs/pcs-xpcs.h>
 #include <linux/phy.h>
 #include <linux/regmap.h>
 #include <net/dsa.h>
@@ -93,6 +94,7 @@ struct ksz_chip_data {
 	bool internal_phy[KSZ_MAX_NUM_PORTS];
 	bool gbit_capable[KSZ_MAX_NUM_PORTS];
 	bool ptp_capable;
+	u8 sgmii_port;
 	const struct regmap_access_table *wr_table;
 	const struct regmap_access_table *rd_table;
 };
@@ -132,6 +134,7 @@ struct ksz_port {
 	u32 force:1;
 	u32 read:1;			/* read MIB counters in background */
 	u32 freeze:1;			/* MIB counter freeze is enabled */
+	u32 sgmii_adv_write:1;
 
 	struct ksz_port_mib mib;
 	phy_interface_t interface;
@@ -141,6 +144,7 @@ struct ksz_port {
 	void *acl_priv;
 	struct ksz_irq pirq;
 	u8 num;
+	struct phylink_pcs *pcs;
 #if IS_ENABLED(CONFIG_NET_DSA_MICROCHIP_KSZ_PTP)
 	struct kernel_hwtstamp_config tstamp_config;
 	bool hwts_tx_en;
@@ -440,6 +444,8 @@ struct ksz_dev_ops {
 	int (*reset)(struct ksz_device *dev);
 	int (*init)(struct ksz_device *dev);
 	void (*exit)(struct ksz_device *dev);
+
+	int (*pcs_create)(struct ksz_device *dev);
 };
 
 struct ksz_device *ksz_switch_alloc(struct device *base, void *priv);
@@ -731,6 +737,21 @@ static inline bool is_lan937x_tx_phy(struct ksz_device *dev, int port)
 		dev->chip_id == LAN9372_CHIP_ID) && port == KSZ_PORT_4;
 }
 
+static inline int ksz_get_sgmii_port(struct ksz_device *dev)
+{
+	return dev->info->sgmii_port - 1;
+}
+
+static inline bool ksz_has_sgmii_port(struct ksz_device *dev)
+{
+	return dev->info->sgmii_port > 0;
+}
+
+static inline bool ksz_is_sgmii_port(struct ksz_device *dev, int port)
+{
+	return dev->info->sgmii_port == port + 1;
+}
+
 /* STP State Defines */
 #define PORT_TX_ENABLE			BIT(2)
 #define PORT_RX_ENABLE			BIT(1)