net: phy: fix WoL handling when suspending the PHY

net: phy: fix WoL handling when suspending the PHY

Actually there's nothing wrong with the two changes marked as "Fixes",
they just revealed a problem which has been existing before.
After having switched r8169 to phylib it was reported that WoL from
shutdown doesn't work any longer (WoL from suspend isn't affected).
Reason is that during shutdown phy_disconnect()->phy_detach()->
phy_suspend() is called.
A similar issue occurs when the phylib state machine calls
phy_suspend() when handling state PHY_HALTED.

Core of the problem is that phy_suspend() suspends the PHY when it
should not due to WoL. phy_suspend() checks for WoL already, but this
works only if the PHY driver handles WoL (what is rarely the case).
Typically WoL is handled by the MAC driver.

phylib knows about this and handles it in mdio_bus_phy_may_suspend(),
but that's used only when suspending the system, not in other cases
like shutdown.

Therefore factor out the relevant check from
mdio_bus_phy_may_suspend() to a new function phy_may_suspend() and
use it in phy_suspend().

Last but not least change phy_detach() to call phy_suspend() before
attached_dev is set to NULL. phy_suspend() accesses attached_dev
when checking whether the MAC driver activated WoL.

Fixes: f1e911d5d0df ("r8169: add basic phylib support")
Fixes: e8cfd9d6c772 ("net: phy: call state machine synchronously in phy_stop")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>