linux-kernel - Re: [PATCH] usb: echi-hcd: Add ehci_setup check before echi

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Message-ID: <Pine.LNX.4.44L0.1605201156220.1938-100000@iolanthe.rowland.org>
Date:	Fri, 20 May 2016 11:57:49 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Andy Gross <andy.gross@...aro.org>
cc:	Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] usb: echi-hcd: Add ehci_setup check before echi_shutdown

On Fri, 20 May 2016, Andy Gross wrote:

> On 20 May 2016 at 09:31, Alan Stern <stern@...land.harvard.edu> wrote:
> > On Thu, 19 May 2016, Andy Gross wrote:
> >
> >> On 19 May 2016 at 05:12, Srinivas Kandagatla
> >> <srinivas.kandagatla@...aro.org> wrote:
> >>
> >> <snip>
> >>
> >> > +++ b/drivers/usb/host/ehci-hcd.c
> >> > @@ -368,6 +368,15 @@ static void ehci_shutdown(struct usb_hcd *hcd)
> >> >  {
> >> >         struct ehci_hcd *ehci = hcd_to_ehci(hcd);
> >> >
> >> > +       /**
> >> > +        * Protect the system from crashing at system shutdown in cases where
> >> > +        * usb host is not added yet from OTG controller driver.
> >> > +        * As ehci_setup() not done yet, so stop accessing registers or
> >> > +        * variables initialized in ehci_setup()
> >> > +        */
> >> > +       if (!ehci->sbrn)
> >> > +               return;
> >> > +
> >> >         spin_lock_irq(&ehci->lock);
> >> >         ehci->shutdown = true;
> >> >         ehci->rh_state = EHCI_RH_STOPPING;
> >>
> >>
> >> Should we also not check this in ehci_suspend and ehci_resume?  If I
> >> do suspend/resume, it crashes in a similar manner.  I know this goes
> >> beyond the problem scope of the patch.  Perhaps I should send in an
> >> additional patch with the code?
> >>
> >> Are there any other places in the ehci-hcd where this needs to be checked?
> >
> > Really, this is an indication that the problem lies not in ehci-hcd but
> > rather in the platform glue code.  The platform code allows itself to
> > be registered as the driver of the controller device but does not
> > initialize the ehci-hcd parts.
> >
> > Neither ehci_suspend nor ehci_resume is called directly by the driver
> > core; the calls all have to pass through the glue code.  So maybe the
> > glue layer needs to be careful about invoking these routines in
> > ehci-hcd before ehci-hcd has been initialized.
> 
> That's a good point.  Perhaps all of this should be in the glue,
> including the shutdown case.

Many of the platform glue files set usb_hcd_platform_shutdown() as 
their shutdown callback, which makes it impossible for them to include 
a controller-specific test.

Alan Stern