[PATCH net v7 2/2] net: phy: take the interrupt back from the bus on detach

[Aleksei Sviridkin <f@lex.la>]

A PHY whose own driver is a module on a filesystem that is not mounted
when the MAC probes gets the generic driver first. phy_probe() replaces
phydev->irq with PHY_POLL because that driver has no interrupt support,
nothing puts it back, and the PHY polls for the rest of the uptime once
its real driver takes over.

Take the number back in phy_detach(), from mdiobus->irq[], which is
where phy_device_create() seeded phydev->irq from and where the bus that
described the interrupt still holds it. Detach is the end of every bind
cycle, so this covers the two substitutions phy_attach_direct() makes as
well as the one in phy_probe(), without any of them having to record
anything.

Doing it here rather than from phy_remove() keeps a single writer on the
rtnl side. phy_attach_direct() is what reads the number back and decides
whether to request an interrupt, and it holds no lock against the driver
core, so a restore driven by an unbind would be racing that decision
rather than ordered against it.

A bus whose driver writes only phydev->irq and never the table is not
covered, because the table then holds PHY_POLL and there is nothing to
take back; lan78xx, smsc95xx and sxgbe are in that position today and
registering the interrupt with the bus is theirs to do.

Assisted-by: LLM
Signed-off-by: Aleksei Sviridkin <f@lex.la>
---
 drivers/net/phy/phy_device.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 94b2e85e00a3..84e2da81dbd3 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -1969,6 +1969,11 @@ void phy_detach(struct phy_device *phydev)
 		phydev->is_genphy_driven = 0;
 	}
 
+	/* Whatever this attachment did to the interrupt, the bus that
+	 * described it still knows the number. Take it back from there.
+	 */
+	phydev->irq = phydev->mdio.bus->irq[phydev->mdio.addr];
+
 	/* Assert the reset signal */
 	phy_device_reset(phydev, 1);
 
-- 
2.53.0