Re: [PATCH net] net: phy: Warn about incorrect mdio_bus_phy_resume() state

[Florian Fainelli]

On 8/16/2022 6:20 AM, Geert Uytterhoeven wrote:
> Hi Florian,
>
> On Fri, Aug 12, 2022 at 6:39 PM Florian Fainelli <f.fainelli@xxxxxxxxx> wrote:
> > On 8/12/22 04:19, Marek Szyprowski wrote:
> > > On 02.08.2022 01:34, Florian Fainelli wrote:
> > > > Calling mdio_bus_phy_resume() with neither the PHY state machine set to
> > > > PHY_HALTED nor phydev->mac_managed_pm set to true is a good indication
> > > > that we can produce a race condition looking like this:
> > > >
> > > > CPU0                                         CPU1
> > > > bcmgenet_resume
> > > >     -> phy_resume
> > > >       -> phy_init_hw
> > > >     -> phy_start
> > > >       -> phy_resume
> > > >                                                    phy_start_aneg()
> > > > mdio_bus_phy_resume
> > > >     -> phy_resume
> > > >        -> phy_write(..., BMCR_RESET)
> > > >         -> usleep()                                  -> phy_read()
> > > >
> > > > with the phy_resume() function triggering a PHY behavior that might have
> > > > to be worked around with (see bf8bfc4336f7 ("net: phy: broadcom: Fix
> > > > brcm_fet_config_init()") for instance) that ultimately leads to an error
> > > > reading from the PHY.
> > > >
> > > > Fixes: fba863b81604 ("net: phy: make PHY PM ops a no-op if MAC driver manages PHY PM")
> > > > Signed-off-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
> > >
> > > This patch, as probably intended, triggers a warning during system
> > > suspend/resume cycle in the SMSC911x driver. I've observed it on ARM
> > > Juno R1 board on the kernel compiled from next-202208010:
> > >
> > >     ------------[ cut here ]------------
> > >     WARNING: CPU: 1 PID: 398 at drivers/net/phy/phy_device.c:323
> > > mdio_bus_phy_resume+0x34/0xc8
>
> I am seeing the same on the ape6evm and kzm9g development
> boards with smsc911x Ethernet, and on various boards with Renesas
> Ethernet (sh_eth or ravb) if Wake-on-LAN is disabled.
>
> > Yes this is catching an actual issue in the driver in that the PHY state
> > machine is still running while the system is trying to suspend. We could
> > go about fixing it in a different number of ways, though I believe this
> > one is probably correct enough to work and fix the warning:
>
> > --- a/drivers/net/ethernet/smsc/smsc911x.c
> > +++ b/drivers/net/ethernet/smsc/smsc911x.c
> > @@ -1037,6 +1037,8 @@ static int smsc911x_mii_probe(struct net_device *dev)
> >                   return ret;
> >           }
> >
> > +       /* Indicate that the MAC is responsible for managing PHY PM */
> > +       phydev->mac_managed_pm = true;
> >           phy_attached_info(phydev);
> >
> >           phy_set_max_speed(phydev, SPEED_100);
> > @@ -2587,6 +2589,8 @@ static int smsc911x_suspend(struct device *dev)
> >           if (netif_running(ndev)) {
> >                   netif_stop_queue(ndev);
> >                   netif_device_detach(ndev);
> > +               if (!device_may_wakeup(dev))
> > +                       phy_suspend(dev->phydev);
> >           }
> >
> >           /* enable wake on LAN, energy detection and the external PME
> > @@ -2628,6 +2632,8 @@ static int smsc911x_resume(struct device *dev)
> >           if (netif_running(ndev)) {
> >                   netif_device_attach(ndev);
> >                   netif_start_queue(ndev);
> > +               if (!device_may_wakeup(dev))
> > +                       phy_resume(dev->phydev);
> >           }
> >
> >           return 0;
>
> Thanks for your patch, but unfortunately this does not work on ape6evm
> and kzm9g, where the smsc911x device is connected to a power-managed
> bus.  It looks like the PHY registers are accessed while the device
> is already suspended, causing a crash during system suspend:

Does it work better if you replace phy_suspend() with phy_stop() and 
phy_resume() with phy_start()?
--
Florian