[PATCH net-next v15 05/13] net: phy: add (*notify_phy_attach/detach)() hooks to struct mii_bus

[Markus Stockhausen <markus.stockhausen@gmx.de>]

From: Daniel Golle <daniel@makrotopia.org>

Some MDIO buses require programming 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 hooks in struct mii_bus

- notify_phy_attach(): called in phy_attach_direct() after PHY
  hardware has been initialized and just before PHY is resumed.
- notify_phy_detach(): called in phy_detach() right after PHY
  has been suspended.

Worth to notice: As of now phy_detach() is not 100% LIFO symmetric
to phy_attach_direct(). E.g. sysfs links are torn down before
suspend while being created before resume. Without reordering of the
detach function the above mentioned notifier placement is the best
possible symmetric implementation. An unconditional call of
notify_phy_detach() was favoured [3].

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/
[3] https://lore.kernel.org/netdev/9e40f50b-357a-4a93-9f59-94847850835d@lunn.ch/#t

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
---
 drivers/net/phy/phy_device.c | 20 ++++++++++++++++----
 include/linux/phy.h          | 18 ++++++++++++++++++
 2 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 2827d2226d6a..de59d864b060 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1737,11 +1737,12 @@ static bool phy_drv_supports_irq(const struct phy_driver *phydrv)
 /**
  * phy_detach_internal - detach a PHY device from its network device
  * @phydev: target phy_device struct
+ * @notify_bus: whether to notify the MDIO bus about the PHY detach
  *
  * This detaches the phy device from its network device and the phy
  * driver, and drops the reference count taken in phy_attach_direct().
  */
-static void phy_detach_internal(struct phy_device *phydev)
+static void phy_detach_internal(struct phy_device *phydev, bool notify_bus)
 {
 	struct net_device *dev = phydev->attached_dev;
 	struct module *ndev_owner = NULL;
@@ -1763,6 +1764,10 @@ static void phy_detach_internal(struct phy_device *phydev)
 				  &dev_attr_phy_standalone.attr);
 
 	phy_suspend(phydev);
+
+	if (notify_bus && phydev->mdio.bus->notify_phy_detach)
+		phydev->mdio.bus->notify_phy_detach(phydev);
+
 	if (dev) {
 		struct hwtstamp_provider *hwprov;
 
@@ -1822,7 +1827,8 @@ static void phy_detach_internal(struct phy_device *phydev)
  */
 void phy_detach(struct phy_device *phydev)
 {
-	phy_detach_internal(phydev);
+	/* cleanup including bus notification */
+	phy_detach_internal(phydev, true);
 }
 EXPORT_SYMBOL(phy_detach);
 
@@ -1968,6 +1974,12 @@ 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);
 
 	/**
@@ -1982,8 +1994,8 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 	return err;
 
 error:
-	/* phy_detach() does all of the cleanup below */
-	phy_detach(phydev);
+	/* phy_detach_internal() does all of the cleanup below */
+	phy_detach_internal(phydev, false);
 	return err;
 
 error_module_put:
diff --git a/include/linux/phy.h b/include/linux/phy.h
index 5f8d65868e0f..3d8afe6b7f1c 100644
--- a/include/linux/phy.h
+++ b/include/linux/phy.h
@@ -376,6 +376,24 @@ 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 for MDIO bus
+	 * drivers. Optional and independent of @notify_phy_detach. Called
+	 * in phy_attach_direct() right before phy_resume(). Runs in process
+	 * context, may sleep and may be called with RTNL held. Must not
+	 * acquire or rely on RTNL. Returns 0 on success or negative errno
+	 * on failure. Must unwind its own state on error as attachment is
+	 * aborted.
+	 */
+	int (*notify_phy_attach)(struct phy_device *phydev);
+	/**
+	 * @notify_phy_detach: Perform pre-detach handling for MDIO bus
+	 * drivers. Optional and independent of @notify_phy_attach. Called
+	 * in phy_detach() right after phy_suspend(). Runs in process context,
+	 * may sleep and may be called with RTNL held. Must not acquire or
+	 * rely on RTNL.
+	 */
+	void (*notify_phy_detach)(struct phy_device *phydev);
 
 	/** @stats: Statistic counters per device on the bus */
 	struct mdio_bus_stats stats[PHY_MAX_ADDR];
-- 
2.55.0