From: Daniel Golle <daniel@makrotopia.org>

Some MDIO buses require to program PHY polling registers depending on
the PHY type. RealTek switch SoCs are the most prominent example of a
DSA switch which doesn't allow to program MAC speed, duplex and
flow-control settings without using PHY polling to do so [1].

Avoid a half-baked solution in the MDIO bus driver because

- it must reinvent the bus scanning to determine the PHYs and
- it must anticipate the right point in time (e.g. deferred PHYs).

Hence there is a need to inform the MDIO bus driver that a PHY is
being attached or detached. Provide two simple hooks in struct
mii_bus which are called

- right after a PHY has been attached
- just before the PHY is going to be detached

Remark! A slightly different version of this patch was part of a
former series [2]. The discussion already showed that an initialization
hook should be placed somewhere late during the whole setup. This
commit implants it right after phy_init_hw() as suggested. On top of
this it adds the detach hook.

[1] https://github.com/openwrt/openwrt/pull/21515#discussion_r2714069716
[2] https://lore.kernel.org/netdev/cover.1769053496.git.daniel@makrotopia.org/ (local)

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Markus Stockhausen <redacted>
---
 drivers/net/phy/phy_device.c | 9 +++++++++
 include/linux/phy.h          | 4 ++++
 2 files changed, 13 insertions(+)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 0615228459ef..676cbf183350 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c

@@ -1876,6 +1876,12 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 	if (err)
 		goto error;
 
+	if (phydev->mdio.bus->notify_phy_attach) {
+		err = phydev->mdio.bus->notify_phy_attach(phydev);
+		if (err)
+			goto error;
+	}
+
 	phy_resume(phydev);
 
 	/**

@@ -1919,6 +1925,9 @@ void phy_detach(struct phy_device *phydev)
 	struct module *ndev_owner = NULL;
 	struct mii_bus *bus;
 
+	if (phydev->mdio.bus->notify_phy_detach)
+		phydev->mdio.bus->notify_phy_detach(phydev);
+
 	if (phydev->devlink) {
 		device_link_del(phydev->devlink);
 		phydev->devlink = NULL;

diff --git a/include/linux/phy.h b/include/linux/phy.h
index 199a7aaa341b..3160ca99deab 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h

@@ -376,6 +376,10 @@ struct mii_bus {
 			 int regnum, u16 val);
 	/** @reset: Perform a reset of the bus */
 	int (*reset)(struct mii_bus *bus);
+	/** @notify_phy_attach: Perform post-attach handling */
+	int (*notify_phy_attach)(struct phy_device *phydev);
+	/** @notify_phy_detach: Perform pre-detach handling */
+	void (*notify_phy_detach)(struct phy_device *phydev);
 
 	/** @stats: Statistic counters per device on the bus */
 	struct mdio_bus_stats stats[PHY_MAX_ADDR];

-- 
2.54.0