[RFC 5/7] net: mdio: Introduce a regmap-based mdio driver

[Maxime Chevallier <maxime.chevallier@bootlin.com>]

There exists several examples today of devices that embed an ethernet
PHY or PCS directly inside an SoC. In this situation, either the device
is controlled through a vendor-specific register set, or sometimes
exposes the standard 802.3 registers that are typically accessed over
MDIO.

As phylib and phylink are designed to use mdiodevices, this driver
allows creating a virtual MDIO bus, that translates mdiodev register
accesses to regmap accesses.

The reason we use regmap is because there are at least 3 such devices
known today, 2 of them are Altera TSE PCS's, memory-mapped, exposed
with a 4-byte stride in stmmac's dwmac-socfpga variant, and a 2-byte
stride in altera-tse. The other one (nxp,sja1110-base-tx-mdio) is
exposed over SPI.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
---
 MAINTAINERS                      |  7 +++
 drivers/net/mdio/Kconfig         | 11 +++++
 drivers/net/mdio/Makefile        |  1 +
 drivers/net/mdio/mdio-regmap.c   | 85 ++++++++++++++++++++++++++++++++
 include/linux/mdio/mdio-regmap.h | 25 ++++++++++
 5 files changed, 129 insertions(+)
 create mode 100644 drivers/net/mdio/mdio-regmap.c
 create mode 100644 include/linux/mdio/mdio-regmap.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 8d5bc223f305..10b3a1800e0d 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12751,6 +12751,13 @@ F:	Documentation/devicetree/bindings/net/ieee802154/mcr20a.txt
 F:	drivers/net/ieee802154/mcr20a.c
 F:	drivers/net/ieee802154/mcr20a.h
 
+MDIO REGMAP DRIVER
+M:	Maxime Chevallier <maxime.chevallier@bootlin.com>
+L:	netdev@vger.kernel.org
+S:	Maintained
+F:	drivers/net/mdio/mdio-regmap.c
+F:	include/linux/mdio/mdio-regmap.h
+
 MEASUREMENT COMPUTING CIO-DAC IIO DRIVER
 M:	William Breathitt Gray <william.gray@linaro.org>
 L:	linux-iio@vger.kernel.org
diff --git a/drivers/net/mdio/Kconfig b/drivers/net/mdio/Kconfig
index 90309980686e..671e4bb82e3e 100644
--- a/drivers/net/mdio/Kconfig
+++ b/drivers/net/mdio/Kconfig
@@ -182,6 +182,17 @@ config MDIO_IPQ8064
 	  This driver supports the MDIO interface found in the network
 	  interface units of the IPQ8064 SoC
 
+config MDIO_REGMAP
+	tristate "Regmap-based virtual MDIO bus driver"
+	depends on REGMAP
+	help
+	  This driver allows using MDIO devices that are not sitting on a
+	  regular MDIO bus, but still exposes the standard 802.3 register
+	  layout. It's regmap-based so that it can be used on integrated,
+	  memory-mapped PHYs, SPI PHYs and so on. A new virtual MDIO bus is
+	  created, and its read/write operations are mapped to the underlying
+	  regmap.
+
 config MDIO_THUNDER
 	tristate "ThunderX SOCs MDIO buses"
 	depends on 64BIT
diff --git a/drivers/net/mdio/Makefile b/drivers/net/mdio/Makefile
index 7d4cb4c11e4e..1015f0db4531 100644
--- a/drivers/net/mdio/Makefile
+++ b/drivers/net/mdio/Makefile
@@ -19,6 +19,7 @@ obj-$(CONFIG_MDIO_MOXART)		+= mdio-moxart.o
 obj-$(CONFIG_MDIO_MSCC_MIIM)		+= mdio-mscc-miim.o
 obj-$(CONFIG_MDIO_MVUSB)		+= mdio-mvusb.o
 obj-$(CONFIG_MDIO_OCTEON)		+= mdio-octeon.o
+obj-$(CONFIG_MDIO_REGMAP)		+= mdio-regmap.o
 obj-$(CONFIG_MDIO_SUN4I)		+= mdio-sun4i.o
 obj-$(CONFIG_MDIO_THUNDER)		+= mdio-thunder.o
 obj-$(CONFIG_MDIO_XGENE)		+= mdio-xgene.o
diff --git a/drivers/net/mdio/mdio-regmap.c b/drivers/net/mdio/mdio-regmap.c
new file mode 100644
index 000000000000..c85d62c2f55c
--- /dev/null
+++ b/drivers/net/mdio/mdio-regmap.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Driver for MMIO-Mapped MDIO devices. Some IPs expose internal PHYs or PCS
+ * within the MMIO-mapped area
+ *
+ * Copyright (C) 2023 Maxime Chevallier <maxime.chevallier@bootlin.com>
+ */
+#include <linux/bitfield.h>
+#include <linux/delay.h>
+#include <linux/mdio.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_mdio.h>
+#include <linux/phy.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/mdio/mdio-regmap.h>
+
+#define DRV_NAME "mdio-regmap"
+
+static int mdio_regmap_read_c22(struct mii_bus *bus, int addr, int regnum)
+{
+	struct mdio_regmap_config *ctx = bus->priv;
+	unsigned int val;
+	int ret;
+
+	if (!(ctx->valid_addr & BIT(addr)))
+		return -ENODEV;
+
+	ret = regmap_read(ctx->regmap, regnum, &val);
+	if (ret < 0)
+		return ret;
+
+	return val;
+}
+
+static int mdio_regmap_write_c22(struct mii_bus *bus, int addr, int regnum,
+				 u16 val)
+{
+	struct mdio_regmap_config *ctx = bus->priv;
+
+	if (!(ctx->valid_addr & BIT(addr)))
+		return -ENODEV;
+
+	return regmap_write(ctx->regmap, regnum, val);
+}
+
+struct mii_bus *devm_mdio_regmap_register(struct device *dev,
+					  const struct mdio_regmap_config *config)
+{
+	struct mdio_regmap_config *mrc;
+	struct mii_bus *mii;
+	int rc;
+
+	if (!config->parent)
+		return ERR_PTR(-EINVAL);
+
+	if (!config->valid_addr)
+		return ERR_PTR(-EINVAL);
+
+	mii = devm_mdiobus_alloc_size(config->parent, sizeof(*mrc));
+	if (!mii)
+		return ERR_PTR(-ENOMEM);
+
+	mrc = mii->priv;
+	memcpy(mrc, config, sizeof(*mrc));
+
+	mrc->regmap = config->regmap;
+	mrc->parent = config->parent;
+	mrc->valid_addr = config->valid_addr;
+
+	mii->name = DRV_NAME;
+	strncpy(mii->id, config->name, MII_BUS_ID_SIZE);
+	mii->parent = config->parent;
+	mii->read = mdio_regmap_read_c22;
+	mii->write = mdio_regmap_write_c22;
+
+	rc = devm_mdiobus_register(dev, mii);
+	if (rc) {
+		dev_err(config->parent, "Cannot register MDIO bus![%s] (%d)\n", mii->id, rc);
+		return ERR_PTR(rc);
+	}
+
+	return mii;
+}
+
diff --git a/include/linux/mdio/mdio-regmap.h b/include/linux/mdio/mdio-regmap.h
new file mode 100644
index 000000000000..ea428e5a2913
--- /dev/null
+++ b/include/linux/mdio/mdio-regmap.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Driver for MMIO-Mapped MDIO devices. Some IPs expose internal PHYs or PCS
+ * within the MMIO-mapped area
+ *
+ * Copyright (C) 2023 Maxime Chevallier <maxime.chevallier@bootlin.com>
+ */
+#ifndef MDIO_REGMAP_H
+#define MDIO_REGMAP_H
+
+#define MDIO_REGMAP_NAME 63
+
+struct device;
+struct regmap;
+
+struct mdio_regmap_config {
+	struct device *parent;
+	struct regmap *regmap;
+	char name[MDIO_REGMAP_NAME];
+	u32 valid_addr;
+};
+
+struct mii_bus *devm_mdio_regmap_register(struct device *dev,
+					  const struct mdio_regmap_config *config);
+
+#endif
-- 
2.39.2