On Wed, 10 Aug 2016, Baolin Wang wrote:
> Considering strict power management for mobile device, we should also power
> off the usb controller if there are no slaves attached even though it is usb
> host function, but it will meet usb device resume failure in below situation.
>
> Suppose that no slave attached ----> usb interface runtime suspend ---->
> usb device runtime suspend -----> xhci suspend -----> power off usb controller.
> After that if the system wants to enter suspend state, then it also will issue
> usb_dev_suspend(), then the pm_runtime_resume() issued in choose_wakeup()
> function will return '-ESHUTDOWN' due to xhci has been suspend and hardware is
> not accessible.
No, this is wrong. The pm_runtime_resume in choose_wakeup() should
cause the xHCI controller to resume also.
> After system entering resume state, if there is slave attached ----> power on
> usb controller ----> xhci resume ----> usb device runtime resume ---->
> usb interface runtime resume. But usb device will resume failed if runtime
> errors is set ('-ESHUTDOWN'), thus we should clear the runtime errors in
> choose_wakeup() function to avoid this situation.
If the controller resumes correctly, this won't be necessary.
Alan Stern
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