netdev - Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption

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Date:	Tue, 16 Sep 2008 15:59:47 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Sebastien Dugue <sebastien.dugue@...l.net>
Cc:	Thomas Klein <osstklei@...ibm.com>, tklein@...ibm.com,
	tinytim@...ibm.com, Linux-rt <linux-rt-users@...r.kernel.org>,
	themann@...ibm.com, netdev@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	jean-pierre.dion@...l.net, linux-ppc <linuxppc-dev@...abs.org>,
	raisch@...ibm.com, gilles.carry@....bull.net
Subject: Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with
	hardirq preemption

On Mon, Sep 15, 2008 at 03:13:32PM +0200, Sebastien Dugue wrote:
[...]
> > we are a bit worried about putting this into the mainstream part of non real
> > time linux.
> 
>   Heck, I sure do not want this to be applied mainstream nor into any tree.
> The sole purpose of this patch was to trigger some reaction from the people who
> know the hardware and try to understand where the problem lies.
> 
> > There interrupts work perfectly fine, and it was a bit of a
> > challenge to get there for all cases / configurations / machines.
> 
>   Agreed, but the fact that it fails with hardirq preemption leads me to
> believe (without any more knowledge about the harware) that there might be
> something amiss with this driver (or the code concerning the XICS)
> nevertheless.
> 
> > 
> > Could you try to enable these changes only for RT-Linux via a real-time
> > kconfig switch?
> 
>   Nope, this is just a quick hack that allows me to have a functional eHEA under
> the rt kernel. I want to understand what the problem is:
> 
>   - Is the eHEA really delivering level interrupts to the XICS?
> 
>   - Is the XICS loosing interrupts when they are masked?

There is a known bug in the -rt kernels, the bug causes handlers
to lose edge interrupts.

See this patch:

http://lkml.org/lkml/2008/6/30/372

>   - ...?

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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