Re: [PATCH v2] USB: Fix the issue of S4 wakeup queisce phase where task resumption fails due to USB status

[Alan Stern]

On Thu, Oct 10, 2024 at 08:46:55AM +0800, Deng Jie wrote:
> Hi Alan
>   I'm thrilled to receive your reply. Thank you very much.
> Sorry for the late response due to the holiday.

> 1. Although during the S4 quiesce phase, the do_remote_wakeup flag is set
> to 0 within the usb_suspend->choose_wakeup function, the subsequent sequence
> of usb_suspend->usb_suspend_both->usb_suspend_device->hcd_bus_suspend->
> xhci_bus_suspend will disable remote wakeup for the RootHub port.
> 2. However, during the loading image phase prior to the S4 quiesce phase,
> the USB device may have generated an interrupt, setting the WAKEUP_PENDING flag.
> Additionally, due to the execution of freeze_kernel_threads before the loading
> image phase, the USB interrupt generated during the loading image phase is
> unable to execute its interrupt handler's bottom half, resulting in the
> WAKEUP_PENDING flag remaining uncleared.
> 3. Therefore, even though the remote wakeup for the RootHub is disabled in
> usb_suspend_both() during the quiesce phase, due to the WAKEUP_PENDING flag not
> being cleared, the xhci still believes that the RootHub has generated a wakeup
> event when it attempts to suspend. Consequently, the xhci suspend function
> returns an -EBUSY error and does not proceed with the suspend operation.
> 
> >Now maybe things are't working the way they are supposed to.  If that's
> >so then you should submit a patch fixing the code so that it _does_ work
> >this way.
> >
> >For instance, in suspend_common(), do_wakeup is derived from
> >device_may_wakeup(rhdev), which is determined by
> >rhdev->power.should_wakeup -- see the definition in
> >include/linux/pm_wakeup.h.  Maybe this flag isn't getting cleared
> >properly.  (In fact, at the moment I don't see where that flag gets set
> >or cleared at all...)
> 
> After configuring CONFIG_PM_SLEEP, the return value of device_may_wakeup
> should be equal to dev->power.can_wakeup && !!dev->power.wakeup.

Please see my reply on this other email thread, which concerns the same 
problem:

https://lore.kernel.org/linux-usb/2c368013-8363-4a4e-bfee-2f0b14d01162@xxxxxxxxxxxxxxxxxxx/

I should have CC'ed you on that message, but I didn't think of it at the 
time.

Alan Stern