netdev - Re: [Bugme-new] [Bug 19992] New: b44 + CONFIG_DEBUG

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Message-Id: <20101011131539.bbb99afe.akpm@linux-foundation.org>
Date:	Mon, 11 Oct 2010 13:15:39 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	james@...anarts.com
Cc:	bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org, netdev@...r.kernel.org,
	Gary Zambrano <zambrano@...adcom.com>
Subject: Re: [Bugme-new] [Bug 19992] New: b44 + CONFIG_DEBUG_SHIRQ (=y on
 fedora) fails to resume


(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Sun, 10 Oct 2010 16:57:11 GMT
bugzilla-daemon@...zilla.kernel.org wrote:

> https://bugzilla.kernel.org/show_bug.cgi?id=19992
> 
>            Summary: b44 + CONFIG_DEBUG_SHIRQ (=y on fedora) fails to
>                     resume
>            Product: Drivers
>            Version: 2.5
>     Kernel Version: 2.6.36-rc7
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: high
>           Priority: P1
>          Component: Network
>         AssignedTo: drivers_network@...nel-bugs.osdl.org
>         ReportedBy: james@...anarts.com
>         Regression: Yes
> 
> 
> b44 network driver causes system to hang on resume when CONFIG_DEBUG_SHIRQ=y.
> I've done some TRACE_RESUME'ing and the following happens:
> * b44_resume() (drivers/net/b44.c) calls request_irq with IRQF_SHARED (after
> freeing it in the suspend function)
> * request_irq() (kernel/irq/manage.c) calls the interrupt handler directly if
> IRQF_SHARED and CONFIG_DEBUG_SHIRQ=y. It says "It's a shared IRQ -- the driver
> ought to be prepared for it to happen immediately, so let's make sure...."
> * b44_interrupt() gets as far as the first br32 and no further:
>   istat = br32(bp, B44_ISTAT);
> 
> I presume it hasn't yet woken the device up so reading a register somehow fails
> and hangs the system.
> 
> If I comment out the code in request_irq() to test the shared irq handler all
> works fine.
> 
> I'm guessing either the b44 driver shouldn't be freeing/requesting irqs in
> suspend/resume functions, or should be resetting the hardware first so that the
> test handler call doesn't fail, but I don't know enough about why it is freeing
> the irq across suspend to be confident fixing it.
> 
> This has been like this for a while (2.6.34 at least). Suspend used to work on
> fedora with this hardware so I think this is a regression. I'm happy to test
> any patches.

Thanks.  Yup, if the driver/device isn't ready to accept an IRQ when
request_irq() is called then there might be a problem should a real
interrupt happen very shortly after request_irq() is called.

The code looks OK to me so perhaps it is indeed some weird hardware
problem.  Maybe a little delay after the ssb_bus_powerup() is needed?

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