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

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

Hi Lukas,

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>

> 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
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland