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Date: Wed, 1 Jun 2005 17:44:07 -0600 (MDT)
From: Zwane Mwaikambo <zwane@arm.linux.org.uk>
To: Nicolas Pitre <nico@cam.org>
cc: Andrea Arcangeli <andrea@suse.de>, Bill Huey <bhuey@lnxw.com>,
       Esben Nielsen <simlo@phys.au.dk>, Thomas Gleixner <tglx@linutronix.de>,
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Subject: Re: RT patch acceptance
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On Wed, 1 Jun 2005, Nicolas Pitre wrote:

> 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.

Hmm that's an interesting case, there are a few others, like MMU,TLB 
update paths and IRQ controller register accesses. But overall these are 
few and easy to identify.

Thanks Nicolas,
	Zwane