linux-kernel - Re: [PATCH PREEMPT_RT]: On AT91 ARM: GPIO Interrupt handling can/will stall forever

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Date:	Wed, 28 Nov 2007 14:04:41 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	Remy Bohmer <linux@...mer.net>, Daniel Walker <dwalker@...sta.com>,
	RT <linux-rt-users@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	ARM Linux Mailing List 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH PREEMPT_RT]: On AT91 ARM: GPIO Interrupt handling can/will
 stall forever



On Wed, 28 Nov 2007, Russell King - ARM Linux wrote:
> On Wed, Nov 28, 2007 at 03:38:11PM +0100, Remy Bohmer wrote:
> > Hello Daniel,
> >
> > >  *      Note: The caller is expected to handle the ack, clear, mask and
> > >  *      unmask issues if necessary.
> > > So we shouldn't need any flow control unless there is some other
> > > factors..
> >
> > This comment can be misinterpreted, I think. Who is assumed to be the
> > caller in this context? The 2 other routines in the driver that
> > actually do the unmasking stuff besides only calling this routine? Is
> > it allowed to call it directly or should it always be done through a
> > wrapper that does all these special things?
>
> The whole point of this simple handler is to accomodate interrupts such
> as those found on the Neponset board.
>
> There, you have a status register in a CPLD but no enable/disable
> registers.  The status register tells you whether the SA1111, ethernet
> or 'USAR' chip asserted its interrupt.
>
> However, as there is no way to disable the sources, this situation has
> to be handled carefully - the function decoding the interrupt source
> needs to mask and unmask the _parent_ interrupt itself, and it's
> exactly that which the comment is directed towards.
>
> See neponset_irq_handler().
>
> The simple IRQ handler is not meant for anything other than that really
> simple implementation.  If people have been using it with interrupts
> which can be individually masked and unmasked, that's where the bug is.
> They should be using one of the other handlers.
>

Russell,

Thanks for the reply and this nice explanation.

I'm taking this as a NACK.

Daniel or Remy, could you find the offending users and make send patches
to fix them.

-- Steve

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