netdev - Re: [PATCH net] net: phy: Warn about incorrect mdio_bus_phy

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Date:   Tue, 16 Aug 2022 19:28:28 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        netdev <netdev@...r.kernel.org>,
        Steve Glendinning <steve.glendinning@...well.net>,
        Doug Berger <opendmb@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        open list <linux-kernel@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Sergey Shtylyov <s.shtylyov@....ru>
Subject: Re: [PATCH net] net: phy: Warn about incorrect mdio_bus_phy_resume()
 state



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@...il.com> 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@...il.com>
>>>
>>> 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