net: phy: fix IRQ-based wake-on-lan over hibernate / power off

net: phy: fix IRQ-based wake-on-lan over hibernate / power off

Uwe reports:
"Most PHYs signal WoL using an interrupt. So disabling interrupts [at
shutdown] breaks WoL at least on PHYs covered by the marvell driver."

Discussing with Ioana, the problem which was trying to be solved was:
"The board in question is a LS1021ATSN which has two AR8031 PHYs that
share an interrupt line. In case only one of the PHYs is probed and
there are pending interrupts on the PHY#2 an IRQ storm will happen
since there is no entity to clear the interrupt from PHY#2's registers.
PHY#1's driver will get stuck in .handle_interrupt() indefinitely."

Further confirmation that "the two AR8031 PHYs are on the same MDIO
bus."

With WoL using interrupts to wake the system, in such a case, the
system will begin booting with an asserted interrupt. Thus, we need to
cope with an interrupt asserted during boot.

Solve this instead by disabling interrupts during PHY probe. This will
ensure in Ioana's situation that both PHYs of the same type sharing an
interrupt line on a common MDIO bus will have their interrupt outputs
disabled when the driver probes the device, but before we hook in any
interrupt handlers - thus avoiding the interrupt storm.

A better fix would be for platform firmware to disable the interrupting
devices at source during boot, before control is handed to the kernel.

Fixes: e2f016cf7751 ("net: phy: add a shutdown procedure")
Link: 20230804071757.383971-1-u.kleine-koenig@pengutronix.de
Reported-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>