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 16:13:07 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Daniel Walker <dwalker@...sta.com>
cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Remy Bohmer <linux@...mer.net>,
	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, Daniel Walker wrote:

>
> Ignoring the ARM side of things for a sec, handle_simple_irq() will
> mask() the interrupt in the special case that an interrupt is already in
> the processes of being handled.. handle_simple_irq() also unmasks when
> it finishes handling an interrupt (something real time adds for some
> reason) ..
>
> In terms of threading the irq everything is the same except there is no
> unmask() call when the thread finishes ..
>

OK, to be honest, I never fully understood the concept of this
"simple_irq". I figured it was because of the ARM architecture.

Your arguments seem reasonable and you are probably correct. But I didn't
write this code, nor do I understand it, and before I go ahead and change
it, I'll wait to hear input from Thomas. Hopefully, he'll be back soon.

Perhaps my confusion about the simple_irq part is from the bug you are
trying to fix. I've been confused by why it was different ;-)

-- Steve

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