Re: [PATCH net-next v3 5/7] usbnet: smsc95xx: Forward PHY interrupts to PHY driver to avoid polling

[Marek Szyprowski <m.szyprowski@samsung.com>]

On 19.05.2022 23:22, Marek Szyprowski wrote:
> On 19.05.2022 21:08, Lukas Wunner wrote:
>> On Tue, May 17, 2022 at 12:18:45PM +0200, Marek Szyprowski wrote:
>>> This patch landed in the recent linux next-20220516 as commit
>>> 1ce8b37241ed ("usbnet: smsc95xx: Forward PHY interrupts to PHY 
>>> driver to
>>> avoid polling"). Unfortunately it breaks smsc95xx usb ethernet 
>>> operation
>>> after system suspend-resume cycle. On the Odroid XU3 board I got the
>>> following warning in the kernel log:
>>>
>>> # time rtcwake -s10 -mmem
>>> rtcwake: wakeup from "mem" using /dev/rtc0 at Tue May 17 09:16:07 2022
>>> PM: suspend entry (deep)
>>> Filesystems sync: 0.001 seconds
>>> Freezing user space processes ... (elapsed 0.002 seconds) done.
>>> OOM killer disabled.
>>> Freezing remaining freezable tasks ... (elapsed 0.001 seconds) done.
>>> printk: Suspending console(s) (use no_console_suspend to debug)
>>> smsc95xx 4-1.1:1.0 eth0: entering SUSPEND2 mode
>>> smsc95xx 4-1.1:1.0 eth0: Failed to read reg index 0x00000114: -113
>>> smsc95xx 4-1.1:1.0 eth0: Error reading MII_ACCESS
>>> smsc95xx 4-1.1:1.0 eth0: __smsc95xx_mdio_read: MII is busy
>>> ------------[ cut here ]------------
>>> WARNING: CPU: 2 PID: 73 at drivers/net/phy/phy.c:946
>>> phy_state_machine+0x98/0x28c
>> [...]
>>> It looks that the driver's suspend/resume operations might need some
>>> adjustments. After the system suspend/resume cycle the driver is not
>>> operational anymore. Reverting the $subject patch on top of linux
>>> next-20220516 restores ethernet operation after system suspend/resume.
>> Thanks a lot for the report.  It seems the PHY is signaling a link 
>> change
>> shortly before system sleep and by the time the phy_state_machine() 
>> worker
>> gets around to handle it, the device has already been suspended and thus
>> refuses any further USB requests with -EHOSTUNREACH (-113):
>>
>> usb_suspend_both()
>>    usb_suspend_interface()
>>      smsc95xx_suspend()
>>        usbnet_suspend()
>>          __usbnet_status_stop_force() # stops interrupt polling,
>>                                       # link change is signaled 
>> before this
>>
>>    udev->can_submit = 0               # refuse further URBs
>>
>> Assuming the above theory is correct, calling phy_stop_machine()
>> after usbnet_suspend() would be sufficient to fix the issue.
>> It cancels the phy_state_machine() worker.
>>
>> The small patch below does that.  Could you give it a spin?
>
> That's it. Your analysis is right and the patch fixes the issue. Thanks!
>
> Feel free to add:
>
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
>
> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>


Gentle ping for the final patch...

It looks that the similar fix is posted for other drivers, i.e.:

https://lore.kernel.org/all/20220825023951.3220-1-f.fainelli@gmail.com/


>
>> Taking a step back though, I'm wondering if there's a bigger problem 
>> here:
>> This is a USB device, so we stop receiving interrupts once the Interrupt
>> Endpoint is no longer polled.  But what if a PHY's interrupt is attached
>> to a GPIO of the SoC and that interrupt is raised while the system is
>> suspending?  The interrupt handler may likewise try to reach an
>> inaccessible (suspended) device.
>>
>> The right thing to do would probably be to signal wakeup.  But the
>> PHY drivers' irq handlers instead schedule the phy_state_machine().
>> Perhaps we need something like the following at the top of
>> phy_state_machine():
>>
>>     if (phydev->suspended) {
>>         pm_wakeup_dev_event(&phydev->mdio.dev, 0, true);
>>         return;
>>     }
>>
>> However, phydev->suspended is set at the *bottom* of phy_suspend(),
>> it would have to be set at the *top* of mdio_bus_phy_suspend()
>> for the above to be correct.  Hmmm...
> Well, your concern sounds valid, but I don't have a board with such hw 
> configuration, so I cannot really test.
>> Thanks,
>>
>> Lukas
>>
>> -- >8 --
>> diff --git a/drivers/net/usb/smsc95xx.c b/drivers/net/usb/smsc95xx.c
>> index bd03e16..d351a6c 100644
>> --- a/drivers/net/usb/smsc95xx.c
>> +++ b/drivers/net/usb/smsc95xx.c
>> @@ -1201,6 +1201,7 @@ static int smsc95xx_bind(struct usbnet *dev, 
>> struct usb_interface *intf)
>>       }
>>         pdata->phydev->irq = phy_irq;
>> +    pdata->phydev->mac_managed_pm = true;
>>       pdata->phydev->is_internal = is_internal_phy;
>>         /* detect device revision as different features may be 
>> available */
>> @@ -1496,6 +1497,9 @@ static int smsc95xx_suspend(struct 
>> usb_interface *intf, pm_message_t message)
>>           return ret;
>>       }
>>   +    if (netif_running(dev->net))
>> +        phy_stop(pdata->phydev);
>> +
>>       if (pdata->suspend_flags) {
>>           netdev_warn(dev->net, "error during last resume\n");
>>           pdata->suspend_flags = 0;
>> @@ -1778,6 +1782,8 @@ static int smsc95xx_resume(struct usb_interface 
>> *intf)
>>       }
>>         phy_init_hw(pdata->phydev);
>> +    if (netif_running(dev->net))
>> +        phy_start(pdata->phydev);
>>         ret = usbnet_resume(intf);
>>       if (ret < 0)
>>
> Best regards

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