linux-kernel - Re: [RFC][PATCH] musb: Avoid musb_gadget_pullup "Unhandled fault" oops on omap4

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Date:	Fri, 29 Jul 2011 08:04:38 +0300
From:	Felipe Balbi <balbi@...com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Felipe Balbi <balbi@...com>, Greg Kroah-Hartman <gregkh@...e.de>,
	lkml <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Nicolas Pitre <nicolas.pitre@...aro.org>
Subject: Re: [RFC][PATCH] musb: Avoid musb_gadget_pullup "Unhandled fault"
 oops on omap4

hi,

On Wed, Jul 20, 2011 at 05:09:34PM -0700, John Stultz wrote:
> I've recently run across an "Unhandled fault: imprecise external abort"
> oops that is caused when a driver called usb_gadget_connect() when there
> was no cable plugged into the musb gadget port.
> 
> You can see the oops message here:
> https://launchpadlibrarian.net/75635123/minicom.txt
> 
> Doing some digging, it seemed the problem was triggered when reading
> from the musb registers in musb_pullup() when the device controller is
> powered down.
> 
> Looking at other examples of where the registers were accessed, I
> noticed they were always enclosed by pm_runtime_get/put calls. So I
> added such calls to the musb_gadget_pullup() function and it seemed to
> resolve the problem.
> 
> Now, full disclosure: this was triggered with the out-of-tree Android
> adb gadget driver. However, I suspect the same behavior could be
> triggered using the composite gadget driver as well, so I think this is
> a generic issue. However, if I'm wrong, let me know and I'll try to make
> sure the fix is done in the right place.
> 
> If this is the right fix, it probably should be queued for 3.1 and
> 3.0-stable.
> 
> Comments and feedback would be greatly appreciated!
> 
> 
> Reported-by: Zach Pfeffer <zach.pfeffer@...aro.org>
> Signed-off-by: John Stultz <john.stultz@...aro.org>

Applied, thanks.

improved commit log slightly:

commit 7e1bb0fdcc9b51ebec0a1e5e06ff075aab55c941
Author: John Stultz <john.stultz@...aro.org>
Date:   Wed Jul 20 17:09:34 2011 -0700

    usb: musb: fix oops on musb_gadget_pullup
    
    an 'unhandled fault' is causes when a gadget driver calls
    usb_gadget_connect() while the USB cable isn't plugged into
    the OTG port.
    
    the fault is caused by an access to MUSB's memory space
    while its clock is turned off due to pm_runtime kicking
    in.
    
    in order to fix the fault, we enclose musb_gadget_pullup()
    with pm_runtime_get_sync() ... pm_runtime_put() calls to
    be sure we will always reach that path with clock turned on.
    
    [ balbi@...com : simplified commit log; removed few things
        which didn't belong there ]
    
    Cc: stable@...nel.org
    Reported-by: Zach Pfeffer <zach.pfeffer@...aro.org>
    Signed-off-by: John Stultz <john.stultz@...aro.org>
    Signed-off-by: Felipe Balbi <balbi@...com>

-- 
balbi

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