[PATCH net-next 2/5] net: pcs: pcs-xpcs-regmap: support XPCS memory-mapped MDIO bus via regmap

[Alex Elder <elder@riscstar.com>]

From: Daniel Thompson <daniel@riscstar.com>

In some DesignWare XPCS implementations 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 <daniel@riscstar.com>
Co-developed-by: Alex Elder <elder@riscstar.com>
Signed-off-by: Alex Elder <elder@riscstar.com>
---
 MAINTAINERS                         |   2 +
 drivers/net/pcs/Makefile            |   3 +-
 drivers/net/pcs/pcs-xpcs-regmap.c   | 169 ++++++++++++++++++++++++++++
 include/linux/pcs/pcs-xpcs-regmap.h |  13 +++
 4 files changed, 186 insertions(+), 1 deletion(-)
 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 55ead3d1007a8..972c9faead5b3 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -27148,8 +27148,10 @@ F:	drivers/net/ethernet/synopsys/
 SYNOPSYS DESIGNWARE ETHERNET XPCS DRIVER
 L:	netdev@vger.kernel.org
 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..088d35f21a4c3 100644
--- a/drivers/net/pcs/Makefile
+++ b/drivers/net/pcs/Makefile
@@ -2,7 +2,8 @@
 # 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-nxp.o pcs-xpcs-regmap.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..f3f3aaaf0b75a
--- /dev/null
+++ b/drivers/net/pcs/pcs-xpcs-regmap.c
@@ -0,0 +1,169 @@
+// 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
+
+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 regmap *regmap, 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(regmap, DW_VR_CSR_VIEWPORT, page);
+	if (res < 0)
+		return res;
+
+	res = regmap_read(regmap, ofs, &val);
+	if (res < 0)
+		return res;
+
+	return val & 0xffff;
+}
+
+static int
+xpcs_regmap_write_reg_indirect(struct regmap *regmap, 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(regmap, DW_VR_CSR_VIEWPORT, page);
+	if (res < 0)
+		return res;
+
+	return regmap_write(regmap, ofs, val);
+}
+
+static int xpcs_regmap_read_c22(struct mii_bus *bus, int addr, int reg)
+{
+	struct regmap *regmap = bus->priv;
+
+	if (addr != 0)
+		return -ENODEV;
+
+	return xpcs_regmap_read_reg_indirect(regmap, MDIO_MMD_VEND2, reg);
+}
+
+static int
+xpcs_regmap_write_c22(struct mii_bus *bus, int addr, int reg, u16 val)
+{
+	struct regmap *regmap = bus->priv;
+
+	if (addr != 0)
+		return -ENODEV;
+
+	return xpcs_regmap_write_reg_indirect(regmap, MDIO_MMD_VEND2, reg, val);
+}
+
+static int xpcs_regmap_read_c45(struct mii_bus *bus, int addr, int dev, int reg)
+{
+	struct regmap *regmap = bus->priv;
+
+	if (addr != 0)
+		return -ENODEV;
+
+	return xpcs_regmap_read_reg_indirect(regmap, dev, reg);
+}
+
+static int xpcs_regmap_write_c45(struct mii_bus *bus, int addr, int dev,
+				 int reg, u16 val)
+{
+	struct regmap *regmap = bus->priv;
+
+	if (addr != 0)
+		return -ENODEV;
+
+	return xpcs_regmap_write_reg_indirect(regmap, 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,
+					  struct regmap *regmap)
+{
+	static atomic_t id = ATOMIC_INIT(-1);
+	struct dw_xpcs *xpcs;
+	struct mii_bus *bus;
+	int ret;
+
+	bus = devm_mdiobus_alloc_size(dev, 0);
+	if (!bus)
+		return ERR_PTR(-ENOMEM);
+
+	bus->name = "DW XPCS MCI/APB3";
+	bus->read = xpcs_regmap_read_c22;
+	bus->write = xpcs_regmap_write_c22;
+	bus->read_c45 = xpcs_regmap_read_c45;
+	bus->write_c45 = xpcs_regmap_write_c45;
+	bus->phy_mask = ~0;
+	bus->parent = dev;
+	bus->priv = regmap;
+
+	snprintf(bus->id, sizeof(bus->id), "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, bus);
+	if (ret) {
+		dev_err(dev, "failed to create MDIO bus\n");
+		return ERR_PTR(ret);
+	}
+
+	xpcs = xpcs_create_mdiodev(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..c6d934b1054ed
--- /dev/null
+++ b/include/linux/pcs/pcs-xpcs-regmap.h
@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef __LINUX_PCS_XPCS_REGMAP_H
+#define __LINUX_PCS_XPCS_REGMAP_H
+
+struct device;
+struct regmap;
+struct dw_xpcs;
+
+struct dw_xpcs *devm_xpcs_regmap_register(struct device *dev,
+					  struct regmap *regmap);
+
+#endif /* __LINUX_PCS_XPCS_REGMAP_H */
-- 
2.53.0