Re: [PATCH] net: phy: phy_device: fix PHY WOL enabled, PM failed to suspend

[Florian Fainelli <f.fainelli@gmail.com>]

On 6/28/2024 9:17 AM, Russell King (Oracle) wrote:
> On Fri, Jun 28, 2024 at 02:03:18PM +0800, Youwan Wang wrote:
>> If the PHY of the mido bus is enabled with Wake-on-LAN (WOL),
>> we cannot suspend the PHY. Although the WOL status has been
>> checked in phy_suspend(), returning -EBUSY(-16) would cause
>> the Power Management (PM) to fail to suspend. Since
>> phy_suspend() is an exported symbol (EXPORT_SYMBOL),
>> timely error reporting is needed. Therefore, an additional
>> check is performed here. If the PHY of the mido bus is enabled
>> with WOL, we skip calling phy_suspend() to avoid PM failure.
>>
>> log:
>> [  322.631362] OOM killer disabled.
>> [  322.631364] Freezing remaining freezable tasks
>> [  322.632536] Freezing remaining freezable tasks completed (elapsed 0.001 seconds)
>> [  322.632540] printk: Suspending console(s) (use no_console_suspend to debug)
>> [  322.633052] YT8521 Gigabit Ethernet stmmac-0:01:
>> PM: dpm_run_callback(): mdio_bus_phy_suspend+0x0/0x110 [libphy] returns -16
>> [  322.633071] YT8521 Gigabit Ethernet stmmac-0:01:
>> PM: failed to suspend: error -16
>> [  322.669699] PM: Some devices failed to suspend, or early wake event detected
>> [  322.669949] OOM killer enabled.
>> [  322.669951] Restarting tasks ... done.
>> [  322.671008] random: crng reseeded on system resumption
>> [  322.671014] PM: suspend exit
>>
>> If the YT8521 driver adds phydrv->flags, ask the YT8521 driver to process
>> WOL at suspend and resume time, the phydev->suspended_by_mdio_bus=1
>> flag would cause the resume failure.

Did you mean to write that if the YT8521 PHY driver entry set the 
PHY_ALWAYS_CALL_SUSPEND flag, then it would cause an error during 
resume? If so, why is that?

> 
> I think the reason this is happening is because the PHY has WoL enabled
> on it without the kernel/netdev driver being aware that WoL is enabled.
> Thus, mdio_bus_phy_may_suspend() returns true, allowing the suspend to
> happen, but then we find unexpectedly that WoL is enabled on the PHY.
> 
> However, whenever a user configures WoL, netdev->wol_enabled will be
> set when _any_ WoL mode is enabled and cleared only if all WoL modes
> are disabled.
> 
> Thus, what we have is a de-sync between the kernel state and hardware
> state, leading to the suspend failing.
> 
> I don't see anything in the motorcomm driver that requires suspend
> if WoL is enabled - yt8521_suspend() first checks to see whether WoL
> is enabled, and exits if it is.
> 
> Andrew - how do you feel about reading the WoL state from the PHY and
> setting netdev->wol_enabled if any WoL is enabled on the PHY? That
> would mean that the netdev's WoL state is consistent with the PHY
> whether or not the user has configured WoL.

Would not the situation described here be solved by having the Motorcomm 
PHY driver set PHY_ALWAYS_CALL_SUSPEND since it deals with checking 
whether WoL is enabled or not and will just return then.
-- 
Florian