Upon system sleep, mdio_bus_phy_suspend() stops the phy_state_machine(),
but subsequent interrupts may retrigger it:

They may have been left enabled to facilitate wakeup and are not
quiesced until the ->suspend_noirq() phase.  Unwanted interrupts may
hence occur between mdio_bus_phy_suspend() and dpm_suspend_noirq(),
as well as between dpm_resume_noirq() and mdio_bus_phy_resume().

Retriggering the phy_state_machine() through an interrupt is not only
undesirable for the reason given in mdio_bus_phy_suspend() (freezing it
midway with phydev->lock held), but also because the PHY may be
inaccessible after it's suspended:  Accesses to USB-attached PHYs are
blocked once usb_suspend_both() clears the can_submit flag and PHYs on
PCI network cards may become inaccessible upon suspend as well.

Amend phy_interrupt() to avoid triggering the state machine if the PHY
is suspended.  Signal wakeup instead if the attached net_device or its
parent has been configured as a wakeup source.  (Those conditions are
identical to mdio_bus_phy_may_suspend().)  Postpone handling of the
interrupt until the PHY has resumed.

Before stopping the phy_state_machine() in mdio_bus_phy_suspend(),
wait for a concurrent phy_interrupt() to run to completion.  That is
necessary because phy_interrupt() may have checked the PHY's suspend
status before the system sleep transition commenced and it may thus
retrigger the state machine after it was stopped.

Likewise, after re-enabling interrupt handling in mdio_bus_phy_resume(),
wait for a concurrent phy_interrupt() to complete to ensure that
interrupts which it postponed are properly rerun.

The issue was exposed by commit 1ce8b37241ed ("usbnet: smsc95xx: Forward
PHY interrupts to PHY driver to avoid polling"), but has existed since
forever.

Fixes: 541cd3ee00a4 ("phylib: Fix deadlock on resume")
Link: https://lore.kernel.org/netdev/a5315a8a-32c2-962f-f696-de9a26d30091@samsung.com/
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: stable@vger.kernel.org # v2.6.33+
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/b7f386d04e9b5b0e2738f0125743e30676f309ef.1656410895.git.lukas@wunner.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>