[RFC PATCH net-next v2 08/10] net: mdio: en8811h: add the nested pass-through bus

[Aleksei Sviridkin <f@lex.la>]

Registering the bus is what publishes the PHY, so it must happen only
once the MD32 is running its firmware. Put the PHY on a bus of its own
rather than on the parent so that the device tree can describe it
normally, interrupts included, and so that the MCU keeps ownership of
the reset line the PHY must not touch.

Only the address the MD32 answers on is passed through; every other
address returns -ENODEV, so scanning this bus cannot produce anything
but this chip's PHY. phy_mask would express the same thing but is not
usable here: of_mdiobus_register() overwrites it before walking the
children. The parent's interrupt for that address is carried over,
since a parent that fills irq[] from its own interrupt domain - a
switch, say - would otherwise leave the PHY polling; an interrupts
property on the PHY's node still wins.

Reach the parent through the mdiobus_*_nested() accessors, which take
its lock at MDIO_MUTEX_NESTED, the way the DSA drivers reach through a
child bus into their parent.

Assisted-by: LLM
Signed-off-by: Aleksei Sviridkin <f@lex.la>
---
 drivers/net/mdio/mdio-airoha-en8811h.c | 134 +++++++++++++++++++++++--
 1 file changed, 128 insertions(+), 6 deletions(-)

diff --git a/drivers/net/mdio/mdio-airoha-en8811h.c b/drivers/net/mdio/mdio-airoha-en8811h.c
index 595b1b72bc01..222aa4b11b95 100644
--- a/drivers/net/mdio/mdio-airoha-en8811h.c
+++ b/drivers/net/mdio/mdio-airoha-en8811h.c
@@ -13,6 +13,8 @@
 #include <linux/mdio.h>
 #include <linux/module.h>
 #include <linux/of.h>
+#include <linux/of_mdio.h>
+#include <linux/phy.h>
 #include <linux/property.h>
 #include <linux/workqueue.h>
 
@@ -26,12 +28,104 @@ struct en8811h_mcu {
 	struct mdio_device *mdiodev;
 	struct gpio_desc *reset_gpio;
 	struct delayed_work fw_poll;
+	struct mii_bus *bus;
 	unsigned int poll_ms;
 	unsigned int waited_ms;
 	u32 fw_version;
 	bool warned;
+	bool fw_running;
 };
 
+static int en8811h_mcu_read(struct mii_bus *bus, int addr, int regnum)
+{
+	struct en8811h_mcu *mcu = bus->priv;
+
+	if (addr != mcu->mdiodev->addr)
+		return -ENODEV;
+
+	return mdiobus_read_nested(mcu->mdiodev->bus, addr, regnum);
+}
+
+static int en8811h_mcu_write(struct mii_bus *bus, int addr, int regnum, u16 val)
+{
+	struct en8811h_mcu *mcu = bus->priv;
+
+	if (addr != mcu->mdiodev->addr)
+		return -ENODEV;
+
+	return mdiobus_write_nested(mcu->mdiodev->bus, addr, regnum, val);
+}
+
+static int en8811h_mcu_read_c45(struct mii_bus *bus, int addr, int devad,
+				int regnum)
+{
+	struct en8811h_mcu *mcu = bus->priv;
+
+	if (addr != mcu->mdiodev->addr)
+		return -ENODEV;
+
+	return mdiobus_c45_read_nested(mcu->mdiodev->bus, addr, devad, regnum);
+}
+
+static int en8811h_mcu_write_c45(struct mii_bus *bus, int addr, int devad,
+				 int regnum, u16 val)
+{
+	struct en8811h_mcu *mcu = bus->priv;
+
+	if (addr != mcu->mdiodev->addr)
+		return -ENODEV;
+
+	return mdiobus_c45_write_nested(mcu->mdiodev->bus, addr, devad, regnum,
+					val);
+}
+
+static int en8811h_mcu_bus_register(struct en8811h_mcu *mcu)
+{
+	struct device *dev = &mcu->mdiodev->dev;
+	struct mii_bus *parent = mcu->mdiodev->bus;
+	struct device_node *np;
+	struct mii_bus *bus;
+	int ret;
+
+	np = of_get_child_by_name(dev->of_node, "mdio");
+	if (!np)
+		return -ENODEV;
+
+	/* Not devm: this is retried, and a devm bus would only be freed at
+	 * detach.
+	 */
+	bus = mdiobus_alloc();
+	if (!bus) {
+		of_node_put(np);
+		return -ENOMEM;
+	}
+
+	bus->name = "airoha-en8811h";
+	snprintf(bus->id, MII_BUS_ID_SIZE, "%s", dev_name(dev));
+	bus->priv = mcu;
+	bus->parent = dev;
+	bus->irq[mcu->mdiodev->addr] = parent->irq[mcu->mdiodev->addr];
+
+	if (parent->read) {
+		bus->read = en8811h_mcu_read;
+		bus->write = en8811h_mcu_write;
+	}
+	if (parent->read_c45) {
+		bus->read_c45 = en8811h_mcu_read_c45;
+		bus->write_c45 = en8811h_mcu_write_c45;
+	}
+
+	ret = of_mdiobus_register(bus, np);
+	of_node_put(np);
+	if (ret) {
+		mdiobus_free(bus);
+		return ret;
+	}
+
+	mcu->bus = bus;
+	return 0;
+}
+
 static void en8811h_mcu_fw_poll(struct work_struct *work)
 {
 	struct en8811h_mcu *mcu = container_of(to_delayed_work(work),
@@ -39,21 +133,35 @@ static void en8811h_mcu_fw_poll(struct work_struct *work)
 	struct device *dev = &mcu->mdiodev->dev;
 	int ret;
 
-	ret = air_en8811h_fw_download(mcu->mdiodev, &mcu->fw_version);
-	if (ret >= 0) {
+	if (!mcu->fw_running) {
+		ret = air_en8811h_fw_download(mcu->mdiodev, &mcu->fw_version);
+		if (ret < 0)
+			goto retry;
+
 		dev_dbg(dev, "firmware %08x running after %ums\n",
 			mcu->fw_version, mcu->waited_ms);
-		return;
+		/* Registration is a new phase: its own backoff and warning. */
+		mcu->fw_running = true;
+		mcu->poll_ms = EN8811H_FW_POLL_MIN_MS;
+		mcu->warned = false;
 	}
 
+	/* fwnode_mdio defers while the PHY node's interrupt controller is
+	 * missing, so a failure here is not necessarily permanent.
+	 */
+	ret = en8811h_mcu_bus_register(mcu);
+	if (!ret)
+		return;
+
+retry:
 	mcu->waited_ms += mcu->poll_ms;
 	if (!mcu->warned && mcu->waited_ms >= EN8811H_FW_WARN_MS) {
-		if (ret == -ENOENT)
+		if (!mcu->fw_running && ret == -ENOENT)
 			dev_warn(dev, "still waiting for %s and %s\n",
 				 EN8811H_MD32_DM, EN8811H_MD32_DSP);
 		else
-			dev_warn(dev, "firmware download keeps failing: %pe\n",
-				 ERR_PTR(ret));
+			dev_warn(dev, "PHY not up after %ums: %pe\n",
+				 mcu->waited_ms, ERR_PTR(ret));
 		mcu->warned = true;
 	}
 
@@ -99,6 +207,7 @@ static int en8811h_mcu_probe(struct mdio_device *mdiodev)
 {
 	struct device *dev = &mdiodev->dev;
 	struct en8811h_mcu *mcu;
+	struct device_node *np;
 
 	mcu = devm_kzalloc(dev, sizeof(*mcu), GFP_KERNEL);
 	if (!mcu)
@@ -107,6 +216,15 @@ static int en8811h_mcu_probe(struct mdio_device *mdiodev)
 	mcu->mdiodev = mdiodev;
 	mdiodev_set_drvdata(mdiodev, mcu);
 
+	/* Registration needs this only once the firmware runs, but a DT
+	 * hole should fail the bind now, not as a work-item error later.
+	 */
+	np = of_get_child_by_name(dev->of_node, "mdio");
+	if (!np)
+		return dev_err_probe(dev, -ENODEV,
+				     "no mdio node describing the PHY\n");
+	of_node_put(np);
+
 	/* The core claims reset-gpios only for devices flagged as PHYs. */
 	mcu->reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_ASIS);
 	if (IS_ERR(mcu->reset_gpio))
@@ -133,6 +251,10 @@ static void en8811h_mcu_remove(struct mdio_device *mdiodev)
 	struct en8811h_mcu *mcu = mdiodev_get_drvdata(mdiodev);
 
 	cancel_delayed_work_sync(&mcu->fw_poll);
+	if (mcu->bus) {
+		mdiobus_unregister(mcu->bus);
+		mdiobus_free(mcu->bus);
+	}
 }
 
 static const struct of_device_id en8811h_mcu_of_match[] = {
-- 
2.53.0