[net-next PATCH v10 6/9] net: mdio: Add Airoha AN8855 Switch MDIO Passtrough

[Christian Marangi <ansuelsmth@gmail.com>]

Add Airoha AN8855 Switch driver to register a MDIO passtrough as switch
address is shared with the internal PHYs and require additional page
handling.

This requires the upper Switch MFD to be probed and init to actually
work.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
---
 MAINTAINERS                    |   1 +
 drivers/net/mdio/Kconfig       |   9 +++
 drivers/net/mdio/Makefile      |   1 +
 drivers/net/mdio/mdio-an8855.c | 113 +++++++++++++++++++++++++++++++++
 4 files changed, 124 insertions(+)
 create mode 100644 drivers/net/mdio/mdio-an8855.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 7f4d7c48b6e1..38c7b2362c92 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -722,6 +722,7 @@ F:	Documentation/devicetree/bindings/net/airoha,an8855-mdio.yaml
 F:	Documentation/devicetree/bindings/net/dsa/airoha,an8855-switch.yaml
 F:	Documentation/devicetree/bindings/nvmem/airoha,an8855-efuse.yaml
 F:	drivers/mfd/airoha-an8855.c
+F:	drivers/net/mdio/mdio-an8855.c
 
 AIROHA ETHERNET DRIVER
 M:	Lorenzo Bianconi <lorenzo@kernel.org>
diff --git a/drivers/net/mdio/Kconfig b/drivers/net/mdio/Kconfig
index 4a7a303be2f7..64fc5c3ef38b 100644
--- a/drivers/net/mdio/Kconfig
+++ b/drivers/net/mdio/Kconfig
@@ -61,6 +61,15 @@ config MDIO_XGENE
 	  This module provides a driver for the MDIO busses found in the
 	  APM X-Gene SoC's.
 
+config MDIO_AN8855
+	tristate "Airoha AN8855 Switch MDIO bus controller"
+	depends on MFD_AIROHA_AN8855
+	depends on OF_MDIO
+	help
+	  This module provides a driver for the Airoha AN8855 Switch
+	  that require a MDIO passtrough as switch address is shared
+	  with the internal PHYs and require additional page handling.
+
 config MDIO_ASPEED
 	tristate "ASPEED MDIO bus controller"
 	depends on ARCH_ASPEED || COMPILE_TEST
diff --git a/drivers/net/mdio/Makefile b/drivers/net/mdio/Makefile
index 1015f0db4531..546c4e55b475 100644
--- a/drivers/net/mdio/Makefile
+++ b/drivers/net/mdio/Makefile
@@ -5,6 +5,7 @@ obj-$(CONFIG_ACPI_MDIO)		+= acpi_mdio.o
 obj-$(CONFIG_FWNODE_MDIO)	+= fwnode_mdio.o
 obj-$(CONFIG_OF_MDIO)		+= of_mdio.o
 
+obj-$(CONFIG_MDIO_AN8855)		+= mdio-an8855.o
 obj-$(CONFIG_MDIO_ASPEED)		+= mdio-aspeed.o
 obj-$(CONFIG_MDIO_BCM_IPROC)		+= mdio-bcm-iproc.o
 obj-$(CONFIG_MDIO_BCM_UNIMAC)		+= mdio-bcm-unimac.o
diff --git a/drivers/net/mdio/mdio-an8855.c b/drivers/net/mdio/mdio-an8855.c
new file mode 100644
index 000000000000..d8a856352842
--- /dev/null
+++ b/drivers/net/mdio/mdio-an8855.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * MDIO passthrough driver for Airoha AN8855 Switch
+ */
+
+#include <linux/mfd/airoha-an8855-mfd.h>
+#include <linux/module.h>
+#include <linux/of_mdio.h>
+#include <linux/platform_device.h>
+
+static int an855_phy_restore_page(struct an8855_mfd_priv *priv,
+				  int phy) __must_hold(&priv->bus->mdio_lock)
+{
+	/* Check PHY page only for addr shared with switch */
+	if (phy != priv->switch_addr)
+		return 0;
+
+	/* Don't restore page if it's not set to switch page */
+	if (priv->current_page != FIELD_GET(AN8855_PHY_PAGE,
+					    AN8855_PHY_PAGE_EXTENDED_4))
+		return 0;
+
+	/* Restore page to 0, PHY might change page right after but that
+	 * will be ignored as it won't be a switch page.
+	 */
+	return an8855_mii_set_page(priv, phy, AN8855_PHY_PAGE_STANDARD);
+}
+
+static int an8855_phy_read(struct mii_bus *bus, int phy, int regnum)
+{
+	struct an8855_mfd_priv *priv = bus->priv;
+	struct mii_bus *real_bus = priv->bus;
+	int ret;
+
+	mutex_lock_nested(&real_bus->mdio_lock, MDIO_MUTEX_NESTED);
+
+	ret = an855_phy_restore_page(priv, phy);
+	if (ret)
+		goto exit;
+
+	ret = __mdiobus_read(real_bus, phy, regnum);
+exit:
+	mutex_unlock(&real_bus->mdio_lock);
+
+	return ret;
+}
+
+static int an8855_phy_write(struct mii_bus *bus, int phy, int regnum, u16 val)
+{
+	struct an8855_mfd_priv *priv = bus->priv;
+	struct mii_bus *real_bus = priv->bus;
+	int ret;
+
+	mutex_lock_nested(&real_bus->mdio_lock, MDIO_MUTEX_NESTED);
+
+	ret = an855_phy_restore_page(priv, phy);
+	if (ret)
+		goto exit;
+
+	ret = __mdiobus_write(real_bus, phy, regnum, val);
+exit:
+	mutex_unlock(&real_bus->mdio_lock);
+
+	return ret;
+}
+
+static int an8855_mdio_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct an8855_mfd_priv *priv;
+	struct mii_bus *bus;
+	int ret;
+
+	/* Get priv of MFD */
+	priv = dev_get_drvdata(dev->parent);
+
+	bus = devm_mdiobus_alloc(dev);
+	if (!bus)
+		return -ENOMEM;
+
+	bus->priv = priv;
+	bus->name = KBUILD_MODNAME "-mii";
+	snprintf(bus->id, MII_BUS_ID_SIZE, KBUILD_MODNAME "-%d",
+		 priv->switch_addr);
+	bus->parent = dev;
+	bus->read = an8855_phy_read;
+	bus->write = an8855_phy_write;
+
+	ret = devm_of_mdiobus_register(dev, bus, dev->of_node);
+	if (ret)
+		dev_err(dev, "failed to register MDIO bus: %d", ret);
+
+	return ret;
+}
+
+static const struct of_device_id an8855_mdio_ids[] = {
+	{ .compatible = "airoha,an8855-mdio", },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, an8855_mdio_ids);
+
+static struct platform_driver an8855_mdio_driver = {
+	.probe	= an8855_mdio_probe,
+	.driver = {
+		.name = "an8855-mdio",
+		.of_match_table = an8855_mdio_ids,
+	},
+};
+module_platform_driver(an8855_mdio_driver);
+
+MODULE_AUTHOR("Christian Marangi <ansuelsmth@gmail.com>");
+MODULE_DESCRIPTION("Driver for AN8855 Mdio passthrough");
+MODULE_LICENSE("GPL");
-- 
2.45.2