Subject: [PATCH net-next v2 03/14] net: pcs: pcs-xpcs-regmap: support XPCS memory-mapped MDIO bus via regmap

From: Alex Elder <[email-masked]>
Date: Thu, 4 Jun 2026 20:00:10 -0500

From: Daniel Thompson <[email-masked]>

In some DesignWare XPCS implementatons the memory-mapped MDIO bus is
allocated to a register window that does not align to a page boundary.
This makes iomapping the registers problematic.

For example the Toshiba TC9564 (a PCIe Ethernet-AVB/TSN bridge) provides
an "eMAC" subsystem with the XPCS base address cuddled up to XGMAC
registers.

Let's introduce helpers to allow the driver that owns the eMAC to register
an XPCS using is regmap for the memory-mapped MDIO bus.

Signed-off-by: Daniel Thompson <[email-masked]>
Signed-off-by: Alex Elder <[email-masked]>
---
 MAINTAINERS                         |   2 +
 drivers/net/pcs/Makefile            |   4 +-
 drivers/net/pcs/pcs-xpcs-regmap.c   | 219 ++++++++++++++++++++++++++++
 include/linux/pcs/pcs-xpcs-regmap.h |  20 +++
 4 files changed, 243 insertions(+), 2 deletions(-)
 create mode 100644 drivers/net/pcs/pcs-xpcs-regmap.c
 create mode 100644 include/linux/pcs/pcs-xpcs-regmap.h

diff --git a/MAINTAINERS b/MAINTAINERS
index eb8cdcc76324f..2aa6ea012c848 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -25931,8 +25931,10 @@ F:	drivers/net/ethernet/synopsys/
 SYNOPSYS DESIGNWARE ETHERNET XPCS DRIVER
 L:	[email-masked]
 S:	Orphan
+F:	drivers/net/pcs/pcs-xpcs-regmap.c
 F:	drivers/net/pcs/pcs-xpcs.c
 F:	drivers/net/pcs/pcs-xpcs.h
+F	include/linux/pcs/pcs-xpcs-regmap.h
 F:	include/linux/pcs/pcs-xpcs.h
 
 SYNOPSYS DESIGNWARE HDMI RX CONTROLLER DRIVER
diff --git a/drivers/net/pcs/Makefile b/drivers/net/pcs/Makefile
index 4f7920618b900..565f1b63fce0b 100644
--- a/drivers/net/pcs/Makefile
+++ b/drivers/net/pcs/Makefile
@@ -1,8 +1,8 @@
 # SPDX-License-Identifier: GPL-2.0
 # Makefile for Linux PCS drivers
 
-pcs_xpcs-$(CONFIG_PCS_XPCS)	:= pcs-xpcs.o pcs-xpcs-plat.o \
-				   pcs-xpcs-nxp.o pcs-xpcs-wx.o
+pcs_xpcs-$(CONFIG_PCS_XPCS)	:= pcs-xpcs.o pcs-xpcs-nxp.o pcs-xpcs-regmap.o \
+				   pcs-xpcs-plat.o pcs-xpcs-wx.o
 
 obj-$(CONFIG_PCS_XPCS)		+= pcs_xpcs.o
 obj-$(CONFIG_PCS_LYNX)		+= pcs-lynx.o
diff --git a/drivers/net/pcs/pcs-xpcs-regmap.c b/drivers/net/pcs/pcs-xpcs-regmap.c
new file mode 100644
index 0000000000000..55cd05d09c7db
--- /dev/null
+++ b/drivers/net/pcs/pcs-xpcs-regmap.c
@@ -0,0 +1,219 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Synopsys DesignWare XPCS regmap helpers
+ *
+ * Copyright (C) 2026 RISCstar Solutions.
+ * Copyright (C) 2024 Serge Semin
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/mdio.h>
+#include <linux/pcs/pcs-xpcs.h>
+#include <linux/pcs/pcs-xpcs-regmap.h>
+#include <linux/regmap.h>
+
+#include "pcs-xpcs.h"
+
+/* Page select register for the indirect MMIO CSRs access */
+#define DW_VR_CSR_VIEWPORT		0xff
+
+struct dw_xpcs_regmap {
+	struct device *dev;
+	struct mii_bus *bus;
+	struct regmap *regmap;
+	bool reg_indir;
+};
+
+static ptrdiff_t xpcs_regmap_addr_format(int dev, int reg)
+{
+	return FIELD_PREP(0x1f0000, dev) | FIELD_PREP(0xffff, reg);
+}
+
+static u16 xpcs_regmap_addr_page(ptrdiff_t csr)
+{
+	return FIELD_GET(0x1fff00, csr);
+}
+
+static ptrdiff_t xpcs_regmap_addr_offset(ptrdiff_t csr)
+{
+	return FIELD_GET(0xff, csr);
+}
+
+static int xpcs_regmap_read_reg_indirect(struct dw_xpcs_regmap *pxpcs, int dev,
+					 int reg)
+{
+	ptrdiff_t csr, ofs;
+	unsigned int val;
+	u16 page;
+	int res;
+
+	csr = xpcs_regmap_addr_format(dev, reg);
+	page = xpcs_regmap_addr_page(csr);
+	ofs = xpcs_regmap_addr_offset(csr);
+
+	res = regmap_write(pxpcs->regmap, DW_VR_CSR_VIEWPORT, page);
+	if (res < 0)
+		return res;
+
+	res = regmap_read(pxpcs->regmap, ofs, &val);
+	if (res < 0)
+		return res;
+
+	return val & 0xffff;
+}
+
+static int xpcs_regmap_write_reg_indirect(struct dw_xpcs_regmap *pxpcs, int dev,
+					  int reg, u16 val)
+{
+	ptrdiff_t csr, ofs;
+	u16 page;
+	int res;
+
+	csr = xpcs_regmap_addr_format(dev, reg);
+	page = xpcs_regmap_addr_page(csr);
+	ofs = xpcs_regmap_addr_offset(csr);
+
+	res = regmap_write(pxpcs->regmap, DW_VR_CSR_VIEWPORT, page);
+	if (res < 0)
+		return res;
+
+	return regmap_write(pxpcs->regmap, ofs, val);
+}
+
+static int xpcs_regmap_read_reg_direct(struct dw_xpcs_regmap *pxpcs, int dev,
+				       int reg)
+{
+	unsigned int val;
+	ptrdiff_t csr;
+	int res;
+
+	csr = xpcs_regmap_addr_format(dev, reg);
+	res = regmap_read(pxpcs->regmap, csr, &val);
+	if (res < 0)
+		return res;
+
+	return val & 0xffff;
+}
+
+static int xpcs_regmap_write_reg_direct(struct dw_xpcs_regmap *pxpcs, int dev,
+					int reg, u16 val)
+{
+	ptrdiff_t csr = xpcs_regmap_addr_format(dev, reg);
+
+	return regmap_write(pxpcs->regmap, csr, val);
+}
+
+static int xpcs_regmap_read_c22(struct mii_bus *bus, int addr, int reg)
+{
+	struct dw_xpcs_regmap *pxpcs = bus->priv;
+
+	if (addr != 0)
+		return -ENODEV;
+
+	if (pxpcs->reg_indir)
+		return xpcs_regmap_read_reg_indirect(pxpcs, MDIO_MMD_VEND2, reg);
+	else
+		return xpcs_regmap_read_reg_direct(pxpcs, MDIO_MMD_VEND2, reg);
+}
+
+static int xpcs_regmap_write_c22(struct mii_bus *bus, int addr, int reg, u16 val)
+{
+	struct dw_xpcs_regmap *pxpcs = bus->priv;
+
+	if (addr != 0)
+		return -ENODEV;
+
+	if (pxpcs->reg_indir)
+		return xpcs_regmap_write_reg_indirect(pxpcs, MDIO_MMD_VEND2, reg, val);
+	else
+		return xpcs_regmap_write_reg_direct(pxpcs, MDIO_MMD_VEND2, reg, val);
+}
+
+static int xpcs_regmap_read_c45(struct mii_bus *bus, int addr, int dev, int reg)
+{
+	struct dw_xpcs_regmap *pxpcs = bus->priv;
+
+	if (addr != 0)
+		return -ENODEV;
+
+	if (pxpcs->reg_indir)
+		return xpcs_regmap_read_reg_indirect(pxpcs, dev, reg);
+	else
+		return xpcs_regmap_read_reg_direct(pxpcs, dev, reg);
+}
+
+static int xpcs_regmap_write_c45(struct mii_bus *bus, int addr, int dev,
+				 int reg, u16 val)
+{
+	struct dw_xpcs_regmap *pxpcs = bus->priv;
+
+	if (addr != 0)
+		return -ENODEV;
+
+	if (pxpcs->reg_indir)
+		return xpcs_regmap_write_reg_indirect(pxpcs, dev, reg, val);
+	else
+		return xpcs_regmap_write_reg_direct(pxpcs, dev, reg, val);
+}
+
+static void devm_xpcs_regmap_destroy(void *data)
+{
+	struct dw_xpcs *xpcs = data;
+
+	xpcs_destroy(xpcs);
+}
+
+struct dw_xpcs *devm_xpcs_regmap_register(struct device *dev,
+					  const struct xpcs_regmap_config *config)
+{
+	static atomic_t id = ATOMIC_INIT(-1);
+	struct dw_xpcs_regmap *pxpcs;
+	struct dw_xpcs *xpcs;
+	int ret;
+
+	pxpcs = devm_kzalloc(dev, sizeof(*pxpcs), GFP_KERNEL);
+	if (!pxpcs)
+		return ERR_PTR(-ENOMEM);
+
+	pxpcs->dev = dev;
+	pxpcs->regmap = config->regmap;
+	pxpcs->reg_indir = config->reg_indir;
+
+	pxpcs->bus = devm_mdiobus_alloc_size(dev, 0);
+	if (!pxpcs->bus)
+		return ERR_PTR(-ENOMEM);
+
+	pxpcs->bus->name = "DW XPCS MCI/APB3";
+	pxpcs->bus->read = xpcs_regmap_read_c22;
+	pxpcs->bus->write = xpcs_regmap_write_c22;
+	pxpcs->bus->read_c45 = xpcs_regmap_read_c45;
+	pxpcs->bus->write_c45 = xpcs_regmap_write_c45;
+	pxpcs->bus->phy_mask = ~0;
+	pxpcs->bus->parent = dev;
+	pxpcs->bus->priv = pxpcs;
+
+	snprintf(pxpcs->bus->id, MII_BUS_ID_SIZE,
+		 "dwxpcs-%x", atomic_inc_return(&id));
+
+	/* MDIO-bus here serves as just a back-end engine abstracting out
+	 * the MDIO and MCI/APB3 IO interfaces utilized for the DW XPCS CSRs
+	 * access.
+	 */
+	ret = devm_mdiobus_register(dev, pxpcs->bus);
+	if (ret) {
+		dev_err(dev, "Failed to create MDIO bus\n");
+		return ERR_PTR(ret);
+	}
+
+	xpcs = xpcs_create_mdiodev(pxpcs->bus, 0);
+	if (IS_ERR(xpcs))
+		return xpcs;
+
+	ret = devm_add_action_or_reset(dev, devm_xpcs_regmap_destroy, xpcs);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return xpcs;
+}
+EXPORT_SYMBOL_GPL(devm_xpcs_regmap_register);
diff --git a/include/linux/pcs/pcs-xpcs-regmap.h b/include/linux/pcs/pcs-xpcs-regmap.h
new file mode 100644
index 0000000000000..19c99d4160365
--- /dev/null
+++ b/include/linux/pcs/pcs-xpcs-regmap.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __LINUX_PCS_XPCS_REGMAP_H
+#define __LINUX_PCS_XPCS_REGMAP_H
+
+#include <linux/types.h>
+
+struct device;
+struct regmap;
+struct dw_xpcs;
+
+struct xpcs_regmap_config {
+	struct regmap *regmap;
+	bool reg_indir;
+};
+
+struct dw_xpcs *devm_xpcs_regmap_register(
+		struct device *dev, const struct xpcs_regmap_config *config);
+
+#endif /* __LINUX_PCS_XPCS_REGMAP_H */
-- 
2.51.0