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

From: Andy Gross <andy.gross@linaro.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-usb@vger.kernel.org,
	Linux Kernel list <linux-kernel@vger.kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] usb: echi-hcd: Add ehci_setup check before echi_shutdown
Date: Fri, 20 May 2016 11:09:00 -0500	[thread overview]
Message-ID: <CAPBZ5Qe3EbTKSihugJ-b8HwvPyQtPXFXVyaeBjY0takuzn+d4A@mail.gmail.com> (raw)
In-Reply-To: <Pine.LNX.4.44L0.1605201156220.1938-100000@iolanthe.rowland.org>

On 20 May 2016 at 10:57, Alan Stern <stern@rowland.harvard.edu> wrote:
> On Fri, 20 May 2016, Andy Gross wrote:
>
>> On 20 May 2016 at 09:31, Alan Stern <stern@rowland.harvard.edu> wrote:
>> > On Thu, 19 May 2016, Andy Gross wrote:
>> >
>> >> On 19 May 2016 at 05:12, Srinivas Kandagatla
>> >> <srinivas.kandagatla@linaro.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.

Yes, I just found this out for myself.  So in that specific case, it
makes sense to have the check within the ehci-hcd.  Whereas in the
glue driver, the suspend/resume use direct calls to
ehci_suspend/resume.

I'll send along a ehci-msm patch to address the issues i see with
suspend/resume.

Thanks!

Andy