AN8811HB needs a MCU soft-reset cycle before firmware loading begins.
Assert the MCU (hold it in reset) and immediately deassert (release)
via a dedicated PBUS register pair (0x5cf9f8 / 0x5cf9fc), accessed
through a registered mdio_device at PHY-addr+8.

Add __air_pbus_reg_write() as a low-level helper taking a struct
mdio_device *, create and register the PBUS mdio_device in
an8811hb_probe() and store it in priv->pbusdev, then implement
an8811hb_mcu_assert() / _deassert() on top of it. Add
an8811hb_remove() to unregister the PBUS device on teardown. Wire
both calls into an8811hb_load_firmware() and en8811h_restart_mcu()
so every firmware load or MCU restart on AN8811HB correctly sequences
the reset control registers.

Fixes: 5afda1d734ed ("net: phy: air_en8811h: add Airoha AN8811HB support")
Signed-off-by: Lucien Jheng <lucienzx159@gmail.com>

---
Changes in v6:
- Include <linux/bitfield.h> and use FIELD_GET() in __air_pbus_reg_write()
  for PBUS register index extraction.
- Introduce AIR_PBUS_REG_ADDR_HIGH_MASK and AIR_PBUS_REG_ADDR_LOW_MASK
  macros to avoid open-coded bit operations.
- Add an8811hb_probe() comment documenting PHY strap constraints
  (addr 8-15), explaining why PHY addr + 8 stays within the valid
  0-31 MDIO address range.

Changes in v5:
- Move the version changelog out of the commit message;
  keep it only in the patch changelog section.

Changes in v4:
- Correct Fixes tag to 5afda1d734ed.
- Refine an8811hb_probe() error paths: split cleanup into err_dev_free and
  err_dev_create so an unregistered PBUS mdio_device is only freed, while a
  registered one is removed then freed. Simplify with fallthrough pattern.

Changes in v3:
- Register a dedicated mdio_device for the PBUS node (addr+8) in
  an8811hb_probe() and store it in priv->pbusdev, replacing the
  inline addr+8 computation in v2.
- Change __air_pbus_reg_write() to take struct mdio_device * instead
  of struct phy_device *.
- Add an8811hb_remove() to unregister and free the PBUS device.
- Fix error handling in an8811hb_probe() with goto error paths to
  ensure the PBUS device is always cleaned up on failure.

Changes in v2:
- Rewrite commit message: The previous wording was ambiguous,
  as it suggested the MCU remains asserted during the entire
  firmware loading process, rather than a quick reset cycle
  before it starts.
  Clarify that assert and deassert is an immediate soft-reset
  cycle to clear MCU state before firmware loading begins.
- Add Fixes: 0a55766b7711 ("net: phy: air_en8811h: add Airoha AN8811HB
  support").
- Change phydev_info() to phydev_dbg() in an8811hb_mcu_assert() and
  an8811hb_mcu_deassert() to avoid noise during normal boot.

 drivers/net/phy/air_en8811h.c | 153 ++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 149 insertions(+), 4 deletions(-)

diff --git a/drivers/net/phy/air_en8811h.c b/drivers/net/phy/air_en8811h.c
index 29ae73e65..a86129ce6 100644
--- a/drivers/net/phy/air_en8811h.c
+++ b/drivers/net/phy/air_en8811h.c
@@ -17,6 +17,7 @@
 #include <linux/phy.h>
 #include <linux/phy/phy-common-props.h>
 #include <linux/firmware.h>
+#include <linux/bitfield.h>
 #include <linux/property.h>
 #include <linux/wordpart.h>
 #include <linux/unaligned.h>
@@ -170,9 +171,23 @@
 #define   AN8811HB_CLK_DRV_CKO_LDPWD		BIT(13)
 #define   AN8811HB_CLK_DRV_CKO_LPPWD		BIT(14)

+#define AN8811HB_MCU_SW_RST		0x5cf9f8
+#define   AN8811HB_MCU_SW_RST_HOLD		BIT(16)
+#define   AN8811HB_MCU_SW_RST_RUN		(BIT(16) | BIT(0))
+#define AN8811HB_MCU_SW_START		0x5cf9fc
+#define   AN8811HB_MCU_SW_START_EN		BIT(16)
+
+/* MII register constants for PBUS access (PHY addr + 8) */
+#define AIR_PBUS_ADDR_HIGH		0x1c
+#define AIR_PBUS_DATA_HIGH		0x10
+#define AIR_PBUS_REG_ADDR_HIGH_MASK	GENMASK(15, 6)
+#define AIR_PBUS_REG_ADDR_LOW_MASK	GENMASK(5, 2)
+
 /* Led definitions */
 #define EN8811H_LED_COUNT	3

+#define EN8811H_PBUS_ADDR_OFFS	8
+
 /* Default LED setup:
  * GPIO5 <-> LED0  On: Link detected, blink Rx/Tx
  * GPIO4 <-> LED1  On: Link detected at 2500 or 1000 Mbps
@@ -201,6 +216,7 @@ struct en8811h_priv {
 	struct clk_hw		hw;
 	struct phy_device	*phydev;
 	unsigned int		cko_is_enabled;
+	struct mdio_device	*pbusdev;
 };

 enum {
@@ -254,6 +270,31 @@ static int air_phy_write_page(struct phy_device *phydev, int page)
 	return __phy_write(phydev, AIR_EXT_PAGE_ACCESS, page);
 }

+static int __air_pbus_reg_write(struct mdio_device *mdiodev,
+				u32 pbus_reg, u32 pbus_data)
+{
+	int ret;
+
+	ret = __mdiobus_write(mdiodev->bus, mdiodev->addr, AIR_EXT_PAGE_ACCESS,
+			      upper_16_bits(pbus_reg));
+	if (ret < 0)
+		return ret;
+
+	ret = __mdiobus_write(mdiodev->bus, mdiodev->addr, AIR_PBUS_ADDR_HIGH,
+			      FIELD_GET(AIR_PBUS_REG_ADDR_HIGH_MASK, pbus_reg));
+	if (ret < 0)
+		return ret;
+
+	ret = __mdiobus_write(mdiodev->bus, mdiodev->addr,
+			      FIELD_GET(AIR_PBUS_REG_ADDR_LOW_MASK, pbus_reg),
+			      lower_16_bits(pbus_data));
+	if (ret < 0)
+		return ret;
+
+	return __mdiobus_write(mdiodev->bus, mdiodev->addr, AIR_PBUS_DATA_HIGH,
+			       upper_16_bits(pbus_data));
+}
+
 static int __air_buckpbus_reg_write(struct phy_device *phydev,
 				    u32 pbus_address, u32 pbus_data)
 {
@@ -570,10 +611,67 @@ static int an8811hb_load_file(struct phy_device *phydev, const char *name,
 	return ret;
 }

+static int an8811hb_mcu_assert(struct phy_device *phydev)
+{
+	struct en8811h_priv *priv = phydev->priv;
+	int ret;
+
+	phy_lock_mdio_bus(phydev);
+
+	ret = __air_pbus_reg_write(priv->pbusdev, AN8811HB_MCU_SW_RST,
+				   AN8811HB_MCU_SW_RST_HOLD);
+	if (ret < 0)
+		goto unlock;
+
+	ret = __air_pbus_reg_write(priv->pbusdev, AN8811HB_MCU_SW_START, 0);
+	if (ret < 0)
+		goto unlock;
+
+	msleep(50);
+	phydev_dbg(phydev, "MCU asserted\n");
+
+unlock:
+	phy_unlock_mdio_bus(phydev);
+	return ret;
+}
+
+static int an8811hb_mcu_deassert(struct phy_device *phydev)
+{
+	struct en8811h_priv *priv = phydev->priv;
+	int ret;
+
+	phy_lock_mdio_bus(phydev);
+
+	ret = __air_pbus_reg_write(priv->pbusdev, AN8811HB_MCU_SW_START,
+				   AN8811HB_MCU_SW_START_EN);
+	if (ret < 0)
+		goto unlock;
+
+	ret = __air_pbus_reg_write(priv->pbusdev, AN8811HB_MCU_SW_RST,
+				   AN8811HB_MCU_SW_RST_RUN);
+	if (ret < 0)
+		goto unlock;
+
+	msleep(50);
+	phydev_dbg(phydev, "MCU deasserted\n");
+
+unlock:
+	phy_unlock_mdio_bus(phydev);
+	return ret;
+}
+
 static int an8811hb_load_firmware(struct phy_device *phydev)
 {
 	int ret;

+	ret = an8811hb_mcu_assert(phydev);
+	if (ret < 0)
+		return ret;
+
+	ret = an8811hb_mcu_deassert(phydev);
+	if (ret < 0)
+		return ret;
+
 	ret = air_buckpbus_reg_write(phydev, EN8811H_FW_CTRL_1,
 				     EN8811H_FW_CTRL_1_START);
 	if (ret < 0)
@@ -662,6 +760,16 @@ static int en8811h_restart_mcu(struct phy_device *phydev)
 {
 	int ret;

+	if (phy_id_compare_model(phydev->phy_id, AN8811HB_PHY_ID)) {
+		ret = an8811hb_mcu_assert(phydev);
+		if (ret < 0)
+			return ret;
+
+		ret = an8811hb_mcu_deassert(phydev);
+		if (ret < 0)
+			return ret;
+	}
+
 	ret = air_buckpbus_reg_write(phydev, EN8811H_FW_CTRL_1,
 				     EN8811H_FW_CTRL_1_START);
 	if (ret < 0)
@@ -1166,6 +1274,7 @@ static int en8811h_leds_setup(struct phy_device *phydev)

 static int an8811hb_probe(struct phy_device *phydev)
 {
+	struct mdio_device *mdiodev;
 	struct en8811h_priv *priv;
 	int ret;

@@ -1175,10 +1284,28 @@ static int an8811hb_probe(struct phy_device *phydev)
 		return -ENOMEM;
 	phydev->priv = priv;

+	/*
+	 * The AN8811HB PHY address is restricted to 8-15 (decimal),
+	 * depending on the board hardware strapping.
+	 * This means the PBUS address is only in the range 16-21 (decimal),
+	 * so we do not need to handle the case
+	 * where the PBUS address exceeds 31 (decimal).
+	 */
+	mdiodev = mdio_device_create(phydev->mdio.bus,
+				     phydev->mdio.addr + EN8811H_PBUS_ADDR_OFFS);
+	if (IS_ERR(mdiodev))
+		return PTR_ERR(mdiodev);
+
+	ret = mdio_device_register(mdiodev);
+	if (ret)
+		goto err_dev_free;
+
+	priv->pbusdev = mdiodev;
+
 	ret = an8811hb_load_firmware(phydev);
 	if (ret < 0) {
 		phydev_err(phydev, "Load firmware failed: %d\n", ret);
-		return ret;
+		goto err_dev_create;
 	}

 	en8811h_print_fw_version(phydev);
@@ -1191,22 +1318,29 @@ static int an8811hb_probe(struct phy_device *phydev)

 	ret = en8811h_leds_setup(phydev);
 	if (ret < 0)
-		return ret;
+		goto err_dev_create;

 	priv->phydev = phydev;
 	/* Co-Clock Output */
 	ret = an8811hb_clk_provider_setup(&phydev->mdio.dev, &priv->hw);
 	if (ret)
-		return ret;
+		goto err_dev_create;

 	/* Configure led gpio pins as output */
 	ret = air_buckpbus_reg_modify(phydev, AN8811HB_GPIO_OUTPUT,
 				      AN8811HB_GPIO_OUTPUT_345,
 				      AN8811HB_GPIO_OUTPUT_345);
 	if (ret < 0)
-		return ret;
+		goto err_dev_create;

 	return 0;
+
+err_dev_create:
+	mdio_device_remove(mdiodev);
+
+err_dev_free:
+	mdio_device_free(mdiodev);
+	return ret;
 }

 static int en8811h_probe(struct phy_device *phydev)
@@ -1561,6 +1695,16 @@ static int en8811h_suspend(struct phy_device *phydev)
 	return genphy_suspend(phydev);
 }

+static void an8811hb_remove(struct phy_device *phydev)
+{
+	struct en8811h_priv *priv = phydev->priv;
+
+	if (priv->pbusdev) {
+		mdio_device_remove(priv->pbusdev);
+		mdio_device_free(priv->pbusdev);
+	}
+}
+
 static struct phy_driver en8811h_driver[] = {
 {
 	PHY_ID_MATCH_MODEL(EN8811H_PHY_ID),
@@ -1587,6 +1731,7 @@ static struct phy_driver en8811h_driver[] = {
 	PHY_ID_MATCH_MODEL(AN8811HB_PHY_ID),
 	.name			= "Airoha AN8811HB",
 	.probe			= an8811hb_probe,
+	.remove			= an8811hb_remove,
 	.get_features		= en8811h_get_features,
 	.config_init		= an8811hb_config_init,
 	.get_rate_matching	= en8811h_get_rate_matching,
--
2.34.1