[PATCH net v12 4/4] net: phy: restore the interrupt when the generic bind cycle fails

[Aleksei Sviridkin <f@lex.la>]

When the generic driver is bound by hand and the bind fails, the PHY is
left with polling in place of its interrupt. phy_probe() has already
replaced phydev->irq with PHY_POLL by then. The unwind does not go
through phy_detach(), so the restore there does not run, and a later
attach finds a PHY that can only be polled.

Found on a Keenetic KN-1012 while adding the restore in phy_detach(),
as the other way out of the same bind cycle.

Save the interrupt number on entry and put it back on the error path.
The bus table is not the right source here. The same label is reached
when a second attach of an already attached PHY fails, and there the
field is live. The table also misses a PHY_MAC_INTERRUPT that a MAC
wrote into phydev->irq.

Tested on the KN-1012 with a 6.18 distribution kernel and an injected
failure of the generic probe: phydev->irq reads 15 afterwards, and -1
with only the restore in phy_detach().

Fixes: 6d9f66ac7fec ("net: phy: Fix PHY module checks and NULL deref in phy_attach_direct()")
Assisted-by: LLM
Signed-off-by: Aleksei Sviridkin <f@lex.la>
---

Notes:
    v12: shorter commit message, no code change.
    
    The Fixes: tag differs from patch 3 because 6d9f66ac7fec split this
    failure off the label that calls phy_detach(). The failure was injected
    with a debug-only module parameter, once for one MDIO address.

 drivers/net/phy/phy_device.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index a9c71a286118..8bfb154402ad 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1755,6 +1755,7 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 	struct mii_bus *bus = phydev->mdio.bus;
 	struct device *d = &phydev->mdio.dev;
 	struct module *ndev_owner = NULL;
+	int irq = phydev->irq;
 	int err;
 
 	/* For Ethernet device drivers that register their own MDIO bus, we
@@ -1896,6 +1897,7 @@ int phy_attach_direct(struct net_device *dev, struct phy_device *phydev,
 
 error_module_put:
 	module_put(d->driver->owner);
+	phydev->irq = irq;
 	phydev->is_genphy_driven = 0;
 	d->driver = NULL;
 error_put_device:
-- 
2.53.0