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

Florian Fainelli
2022-08-17T02:28:40Z

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@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()?
--
Florian