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

Marek Szyprowski
2022-08-17T11:32:53Z

On 17.08.2022 11:18, Geert Uytterhoeven wrote:
> On Wed, Aug 17, 2022 at 4:28 AM Florian Fainelli <f.fainelli@gmail.com> wrote:
>> On 8/16/2022 6:20 AM, Geert Uytterhoeven wrote:
>>> On Fri, Aug 12, 2022 at 6:39 PM Florian Fainelli <f.fainelli@gmail.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@gmail.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()?
> Thank you, much better!
> Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

It also works for me.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland