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

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Message-ID: <20071128230331.GA31730@flint.arm.linux.org.uk>
Date:	Wed, 28 Nov 2007 23:03:32 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Daniel Walker <dwalker@...sta.com>, 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, Nov 28, 2007 at 04:13:07PM -0500, Steven Rostedt wrote:
> 
> 
> 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.

If you read what I said compared with what Daniel said, you'll see that
adding the mask/unmask is _pointless_ because for the case where the
simple handler should be used, there is _no_ hardware masking available
except via the parent interrupt signal.

So actually Daniel's argument misses the basic point - that using
handle_simple_irq for non-simple IRQs is just WRONG.
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