net: pcs: xpcs: add support for NXP SJA1105

The NXP SJA1105 DSA switch integrates a Synopsys SGMII XPCS on port 4.
The generic code works fine, except there is an integration issue which
needs to be dealt with: in this switch, the XPCS is integrated with a
PMA that has the TX lane polarity inverted by default (PLUS is MINUS,
MINUS is PLUS).

To obtain normal non-inverted behavior, the TX lane polarity must be
inverted in the PCS, via the DIGITAL_CONTROL_2 register.

We introduce a pma_config() method in xpcs_compat which is called by the
phylink_pcs_config() implementation.

Also, the NXP SJA1105 returns all zeroes in the PHY ID registers 2 and 3.
We need to hack up an ad-hoc PHY ID (OUI is zero, device ID is 1) in
order for the XPCS driver to recognize it. This PHY ID is added to the
public include/linux/pcs/pcs-xpcs.h for that reason (for the sja1105
driver to be able to use it in a later patch).

Signed-off-by: Vladimir Oltean <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

MAINTAINERS

···
 L:	[e-mail]
 S:	Maintained
 F:	drivers/net/dsa/sja1105
+F:	drivers/net/pcs/pcs-xpcs-nxp.c
 
 NXP TDA998X DRM DRIVER
 M:	Russell King <[e-mail]>

drivers/net/pcs/Makefile

···
 # SPDX-License-Identifier: GPL-2.0
 # Makefile for Linux PCS drivers
 
-obj-$(CONFIG_PCS_XPCS)		+= pcs-xpcs.o
+pcs_xpcs-$(CONFIG_PCS_XPCS)	:= pcs-xpcs.o pcs-xpcs-nxp.o
+
+obj-$(CONFIG_PCS_XPCS)		+= pcs_xpcs.o
 obj-$(CONFIG_PCS_LYNX)		+= pcs-lynx.o

drivers/net/pcs/pcs-xpcs-nxp.c

···
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright 2021 NXP Semiconductors
+ */
+#include <linux/pcs/pcs-xpcs.h>
+#include "pcs-xpcs.h"
+
+/* In NXP SJA1105, the PCS is integrated with a PMA that has the TX lane
+ * polarity inverted by default (PLUS is MINUS, MINUS is PLUS). To obtain
+ * normal non-inverted behavior, the TX lane polarity must be inverted in the
+ * PCS, via the DIGITAL_CONTROL_2 register.
+ */
+int nxp_sja1105_sgmii_pma_config(struct dw_xpcs *xpcs)
+{
+	return xpcs_write(xpcs, MDIO_MMD_VEND2, DW_VR_MII_DIG_CTRL2,
+			  DW_VR_MII_DIG_CTRL2_TX_POL_INV);
+}

drivers/net/pcs/pcs-xpcs.c

···
 	const phy_interface_t *interface;
 	int num_interfaces;
 	int an_mode;
+	int (*pma_config)(struct dw_xpcs *xpcs);
 };
 
 struct xpcs_id {
···
 #define xpcs_linkmode_supported(compat, mode) \
 	__xpcs_linkmode_supported(compat, ETHTOOL_LINK_MODE_ ## mode ## _BIT)
 
-static int xpcs_read(struct dw_xpcs *xpcs, int dev, u32 reg)
+int xpcs_read(struct dw_xpcs *xpcs, int dev, u32 reg)
 {
 	u32 reg_addr = mdiobus_c45_addr(dev, reg);
 	struct mii_bus *bus = xpcs->mdiodev->bus;
···
 	return mdiobus_read(bus, addr, reg_addr);
 }
 
-static int xpcs_write(struct dw_xpcs *xpcs, int dev, u32 reg, u16 val)
+int xpcs_write(struct dw_xpcs *xpcs, int dev, u32 reg, u16 val)
 {
 	u32 reg_addr = mdiobus_c45_addr(dev, reg);
 	struct mii_bus *bus = xpcs->mdiodev->bus;
···
 		return -1;
 	}
 
+	if (compat->pma_config) {
+		ret = compat->pma_config(xpcs);
+		if (ret)
+			return ret;
+	}
+
 	return 0;
 }
 
···
 	},
 };
 
+static const struct xpcs_compat nxp_sja1105_xpcs_compat[DW_XPCS_INTERFACE_MAX] = {
+	[DW_XPCS_SGMII] = {
+		.supported = xpcs_sgmii_features,
+		.interface = xpcs_sgmii_interfaces,
+		.num_interfaces = ARRAY_SIZE(xpcs_sgmii_interfaces),
+		.an_mode = DW_AN_C37_SGMII,
+		.pma_config = nxp_sja1105_sgmii_pma_config,
+	},
+};
+
 static const struct xpcs_id xpcs_id_list[] = {
 	{
 		.id = SYNOPSYS_XPCS_ID,
 		.mask = SYNOPSYS_XPCS_MASK,
 		.compat = synopsys_xpcs_compat,
+	}, {
+		.id = NXP_SJA1105_XPCS_ID,
+		.mask = SYNOPSYS_XPCS_MASK,
+		.compat = nxp_sja1105_xpcs_compat,
 	},
 };
 

drivers/net/pcs/pcs-xpcs.h

···
 /* EEE Mode Control Register */
 #define DW_VR_MII_EEE_MCTRL0		0x8006
 #define DW_VR_MII_EEE_MCTRL1		0x800b
+#define DW_VR_MII_DIG_CTRL2		0x80e1
 
 /* VR_MII_DIG_CTRL1 */
 #define DW_VR_MII_DIG_CTRL1_MAC_AUTO_SW		BIT(9)
+
+/* VR_MII_DIG_CTRL2 */
+#define DW_VR_MII_DIG_CTRL2_TX_POL_INV		BIT(4)
+#define DW_VR_MII_DIG_CTRL2_RX_POL_INV		BIT(0)
 
 /* VR_MII_AN_CTRL */
 #define DW_VR_MII_AN_CTRL_TX_CONFIG_SHIFT	3
···
 
 /* VR MII EEE Control 1 defines */
 #define DW_VR_MII_EEE_TRN_LPI		BIT(0)	/* Transparent Mode Enable */
+
+int xpcs_read(struct dw_xpcs *xpcs, int dev, u32 reg);
+int xpcs_write(struct dw_xpcs *xpcs, int dev, u32 reg, u16 val);
+
+int nxp_sja1105_sgmii_pma_config(struct dw_xpcs *xpcs);

include/linux/pcs/pcs-xpcs.h

···
 #include <linux/phy.h>
 #include <linux/phylink.h>
 
+#define NXP_SJA1105_XPCS_ID		0x00000010
+
 /* AN mode */
 #define DW_AN_C73			1
 #define DW_AN_C37_SGMII			2