Re: [PATCH] usb: host: ehci: workaround PME bug on AMD EHCI controller

From: Kai-Heng Feng
Date: Mon Jun 19 2017 - 22:37:07 EST

On Tue, Jun 20, 2017 at 2:32 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> It's possible that the test was invalid. Kai-Heng did not say whether
> /sys/.../power/wakeup was set to "enabled" for both the EHCI controller
> and the USB root hub beneath it, before the test was started. If
> either of them was set to "disabled" then we would not expect a plug or
> unplug event to wake up the system.

You are right, it's "disabled" on USB root hub.
Changed it to "enabled", the test result remains the same.

> In any case, the controller should be set to the lowest power setting
> that is consistent with the desired wakeup behavior. If wakeup is set
> to "enabled" then the state should be D2 -- if possible. That's the
> theory, anyway. If the system supports putting devices only into D3
> during S3 sleep then there's no choice, but if we do have a choice then
> we should take it.
> BTW, I just noticed that pci_target_state() uses device_may_wakeup() to
> get the desired wakeup behavior. That is correct for system sleep, but
> it is wrong for runtime PM. For runtime PM, wakeup should be enabled
> whenever the hardware allows it, so the test should be
> device_can_wakeup().
> This means that pci_target_state() should behave differently depending
> on whether it is called from pci_prepare_to_sleep() or from
> pci_finish_runtime_suspend(). Probably nobody noticed this before
> because it usually doesn't make any difference.
> Alan Stern