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

From: Steven Rostedt <rostedt@goodmis.org>
To: Daniel Walker <dwalker@mvista.com>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>,
	Remy Bohmer <linux@bohmer.net>,
	RT <linux-rt-users@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	ARM Linux Mailing List  <linux-arm-kernel@lists.arm.linux.org.uk>,
	Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH PREEMPT_RT]: On AT91 ARM: GPIO Interrupt handling can/will stall forever
Date: Wed, 28 Nov 2007 16:13:07 -0500 (EST)	[thread overview]
Message-ID: <Pine.LNX.4.58.0711281608490.26365@gandalf.stny.rr.com> (raw)
In-Reply-To: <1196282672.27964.32.camel@imap.mvista.com>

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