linux-kernel - Re: [PATCH] usb: core: Add runtime resume checking

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Message-ID: <20160811084430.GF18967@shlinux2>
Date:	Thu, 11 Aug 2016 16:44:30 +0800
From:	Peter Chen <hzpeterchen@...il.com>
To:	Baolin Wang <baolin.wang@...aro.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Greg KH <gregkh@...uxfoundation.org>, stefan.koch10@...il.com,
	Oliver Neukum <oneukum@...e.com>,
	Muhammad Falak R Wani <falakreyaz@...il.com>,
	Mark Brown <broonie@...nel.org>,
	USB <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: core: Add runtime resume checking

On Thu, Aug 11, 2016 at 04:41:27PM +0800, Baolin Wang wrote:
> >> >>
> >> >> OK. But that is a real problem. It will pm_runtime_resume() falied
> >> >> (issued in choose_wakeup()), cause usb controller has powered-off and
> >> >> xHCI controller has suspended and we have no method to notify the user
> >> >> to power-on USB controller. Any good suggestion to solve this, Alan
> >> >> and Peter? Thanks.
> >> >>
> >> >
> >> > Maybe you can show us the call stack why pm_runtime_resume has failed
> >> > at your environment.
> >>
> >> OK. I try to explain it at below:
> >>
> >> For example: No slave attached----> usb interface runtime suspend
> >> ----> usb device runtime suspend (routine is:
> >> usb_suspend_device()--->generic_suspend() --> hcd_bus_suspend()-->
> >> xhci_bus_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() function (issued in choose_wakeup() function) will
> >> return -ESHUTDOWN due to xhci has been suspend and hardware is not accessible.
> >>
> >> We issue the pm_runtime_resume() function routine: usb_resume_device()
> >> ----> generic_resume() ----> hcd_bus_resume() ---> xhci_bus_resume(),
> >> but now xHCI is not accessible due to xhci_suspend() is issued and USB
> >> controller is power off when no slave attached. That is why
> >> pm_runtime_resume failed.
> >>
> >
> > What host controller driver you are using? Assume you are using
> > xhci-plat.c. The problem for you is this driver does not implement
> 
> Yes. I use xhci-plat.c.
> 
> > runtime pm operations, so the flag HCD_FLAG_HW_ACCESSIBLE is not set.
> > Maybe Robert's patch is a good start for you [1]
> >
> > [1] http://www.spinics.net/lists/linux-usb/msg144602.html
> 
> OK. Maybe I need to implement the runtime PM callbacks for xhci-plat, right?
> 

I think so.

-- 

Best Regards,
Peter Chen