[RFC PATCH] drivers: net: dsa: b53: mmap: add phy ops

["Álvaro Fernández Rojas" <noltari@gmail.com>]

Currently, B53 MMAP BCM63xx devices with an external switch hang when
performing PHY read and write operations due to invalid registers access.
This adds support for PHY ops by using the internal bus from mdio-mux-bcm6368
when probed by device tree and also falls back to direct MDIO registers if not.

This is an alternative to:
- https://patchwork.kernel.org/project/netdevbpf/cover/20230317113427.302162-1-noltari@gmail.com/
- https://patchwork.kernel.org/project/netdevbpf/patch/20230317113427.302162-2-noltari@gmail.com/
- https://patchwork.kernel.org/project/netdevbpf/patch/20230317113427.302162-3-noltari@gmail.com/
- https://patchwork.kernel.org/project/netdevbpf/patch/20230317113427.302162-4-noltari@gmail.com/
As discussed, it was an ABI break and not the correct way of fixing the issue.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
---
 drivers/net/dsa/b53/b53_mmap.c    | 86 +++++++++++++++++++++++++++++++
 include/linux/platform_data/b53.h |  1 +
 2 files changed, 87 insertions(+)

diff --git a/drivers/net/dsa/b53/b53_mmap.c b/drivers/net/dsa/b53/b53_mmap.c
index 706df04b6cee..7deca1c557c5 100644
--- a/drivers/net/dsa/b53/b53_mmap.c
+++ b/drivers/net/dsa/b53/b53_mmap.c
@@ -19,14 +19,25 @@
 #include <linux/bits.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
+#include <linux/of_mdio.h>
 #include <linux/io.h>
 #include <linux/platform_device.h>
 #include <linux/platform_data/b53.h>
 
 #include "b53_priv.h"
 
+#define REG_MDIOC		0xb0
+#define  REG_MDIOC_EXT_MASK	BIT(16)
+#define  REG_MDIOC_REG_SHIFT	20
+#define  REG_MDIOC_PHYID_SHIFT	25
+#define  REG_MDIOC_RD_MASK	BIT(30)
+#define  REG_MDIOC_WR_MASK	BIT(31)
+
+#define REG_MDIOD		0xb4
+
 struct b53_mmap_priv {
 	void __iomem *regs;
+	struct mii_bus *bus;
 };
 
 static int b53_mmap_read8(struct b53_device *dev, u8 page, u8 reg, u8 *val)
@@ -216,6 +227,69 @@ static int b53_mmap_write64(struct b53_device *dev, u8 page, u8 reg,
 	return 0;
 }
 
+static inline void b53_mmap_mdio_read(struct b53_device *dev, int phy_id,
+				      int loc, u16 *val)
+{
+	uint32_t reg;
+
+	b53_mmap_write32(dev, 0, REG_MDIOC, 0);
+
+	reg = REG_MDIOC_RD_MASK |
+	      (phy_id << REG_MDIOC_PHYID_SHIFT) |
+	      (loc << REG_MDIOC_REG_SHIFT);
+
+	b53_mmap_write32(dev, 0, REG_MDIOC, reg);
+	udelay(50);
+	b53_mmap_read16(dev, 0, REG_MDIOD, val);
+}
+
+static inline int b53_mmap_mdio_write(struct b53_device *dev, int phy_id,
+				      int loc, u16 val)
+{
+	uint32_t reg;
+
+	b53_mmap_write32(dev, 0, REG_MDIOC, 0);
+
+	reg = REG_MDIOC_WR_MASK |
+	      (phy_id << REG_MDIOC_PHYID_SHIFT) |
+	      (loc << REG_MDIOC_REG_SHIFT) |
+	      val;
+
+	b53_mmap_write32(dev, 0, REG_MDIOC, reg);
+	udelay(50);
+
+	return 0;
+}
+
+static int b53_mmap_phy_read16(struct b53_device *dev, int addr, int reg,
+			       u16 *value)
+{
+	struct b53_mmap_priv *priv = dev->priv;
+	struct mii_bus *bus = priv->bus;
+
+	if (bus)
+		*value = mdiobus_read_nested(bus, addr, reg);
+	else
+		b53_mmap_mdio_read(dev, addr, reg, value);
+
+	return 0;
+}
+
+static int b53_mmap_phy_write16(struct b53_device *dev, int addr, int reg,
+				u16 value)
+{
+	struct b53_mmap_priv *priv = dev->priv;
+	struct mii_bus *bus = priv->bus;
+	int ret;
+
+	if (bus)
+		ret = mdiobus_write_nested(bus, addr, reg, value);
+	else
+		ret = b53_mmap_mdio_write(dev, addr, reg, value);
+
+	return ret;
+}
+
 static const struct b53_io_ops b53_mmap_ops = {
 	.read8 = b53_mmap_read8,
 	.read16 = b53_mmap_read16,
@@ -227,6 +301,8 @@ static const struct b53_io_ops b53_mmap_ops = {
 	.write32 = b53_mmap_write32,
 	.write48 = b53_mmap_write48,
 	.write64 = b53_mmap_write64,
+	.phy_read16 = b53_mmap_phy_read16,
+	.phy_write16 = b53_mmap_phy_write16,
 };
 
 static int b53_mmap_probe_of(struct platform_device *pdev,
@@ -234,6 +310,7 @@ static int b53_mmap_probe_of(struct platform_device *pdev,
 {
 	struct device_node *np = pdev->dev.of_node;
 	struct device_node *of_ports, *of_port;
+	struct device_node *mdio;
 	struct device *dev = &pdev->dev;
 	struct b53_platform_data *pdata;
 	void __iomem *mem;
@@ -251,6 +328,14 @@ static int b53_mmap_probe_of(struct platform_device *pdev,
 	pdata->chip_id = (u32)device_get_match_data(dev);
 	pdata->big_endian = of_property_read_bool(np, "big-endian");
 
+	mdio = of_parse_phandle(np, "mii-bus", 0);
+	if (!mdio)
+		return -EINVAL;
+
+	pdata->bus = of_mdio_find_bus(mdio);
+	if (!pdata->bus)
+		return -EPROBE_DEFER;
+
 	of_ports = of_get_child_by_name(np, "ports");
 	if (!of_ports) {
 		dev_err(dev, "no ports child node found\n");
@@ -297,6 +382,7 @@ static int b53_mmap_probe(struct platform_device *pdev)
 		return -ENOMEM;
 
 	priv->regs = pdata->regs;
+	priv->bus = pdata->bus;
 
 	dev = b53_switch_alloc(&pdev->dev, &b53_mmap_ops, priv);
 	if (!dev)
diff --git a/include/linux/platform_data/b53.h b/include/linux/platform_data/b53.h
index 6f6fed2b171d..be0c5bfdedad 100644
--- a/include/linux/platform_data/b53.h
+++ b/include/linux/platform_data/b53.h
@@ -32,6 +32,7 @@ struct b53_platform_data {
 	/* only used by MMAP'd driver */
 	unsigned big_endian:1;
 	void __iomem *regs;
+	struct mii_bus *bus;
 };
 
 #endif
-- 
2.30.2