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Date: Wed, 01 Jun 2005 18:29:37 -0400 (EDT)
From: Nicolas Pitre <nico@cam.org>
Subject: Re: RT patch acceptance
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To: Andrea Arcangeli <andrea@suse.de>
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On Wed, 1 Jun 2005, Andrea Arcangeli wrote:

> On Wed, Jun 01, 2005 at 05:29:48PM -0400, Nicolas Pitre wrote:
> > Actualy it's RTAI/rtlinux which is broken wrt the above IRQ disable.
> > See for yourself when they're used and watch RTAI/rtlinux crash.  
> 
> Well it's not so clear so please elaborate since I'm curious. Especially
> it'd be interesting to know if this is that an arm specific kernel
> crash, or would it happen on x86 too?

It would happen on any architecture supporting XIP from flash.

The XIP code therefore polls the IRQ controller (with IRQs masked out) 
and whenever an IRQ is pending the flash operation is suspended and IRQs 
unmasked.  In this case the hard IRQ latency is function of the flash 
suspend delay which is documented in the datasheet.

> There sure can be arch dependencies where an hard_local_irq_disable can
> be necessary in some places, but that's quite a separate topic, and on
> x86 I don't see why it should crash.

It would crash if the kernel is XIP.  If not XIP then the 
local_irq_save() is never encountered in that case.


Nicolas