linux-kernel - Re: [PATCH] ehea: Add kdump support

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Message-Id: <1196091697.7513.30.camel@luke-laptop.br.ibm.com>
Date:	Mon, 26 Nov 2007 13:41:37 -0200
From:	Luke Browning <lukebr@...ux.vnet.ibm.com>
To:	michael@...erman.id.au
Cc:	Thomas Klein <osstklei@...ibm.com>,
	Michael Neuling <mikey@...ling.org>,
	Jeff Garzik <jeff@...zik.org>,
	Jan-Bernd Themann <themann@...ibm.com>,
	netdev <netdev@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-ppc <linuxppc-dev@...abs.org>,
	Christoph Raisch <raisch@...ibm.com>,
	Paul Mackerras <paulus@...ba.org>,
	Marcus Eder <meder@...ibm.com>,
	Stefan Roscher <stefan.roscher@...ibm.com>
Subject: Re: [PATCH] ehea: Add kdump support

On Mon, 2007-11-26 at 19:16 +1100, Michael Ellerman wrote:

> 
> Hi Thomas,
> 
> I'm sorry, but this patch is all wrong IMHO.
> 
> For kdump we have to assume that the kernel is fundamentally broken,
> we've panicked, so something bad has happened - every line of kernel
> code that is run decreases the chance that we'll successfully make it
> into the kdump kernel.

I agree with Michael.

> Solutions that might be better:
> 
>  a) if there are a finite number of handles and we can predict their 
>     values, just delete them all in the kdump kernel before the driver
>     loads.

This is a good solution if handles are predefined.

>  b) if there are a small & finite number of handles, save their values 
>     in a device tree property and have the kdump kernel read them and 
>     delete them before the driver loads.

Also good but is more complicated.  

>  c) if neither of those work, provide a minimal routine that _only_
>     deletes the handles in the crashed kernel.
>  d) <something else>

Can the driver or configuration method for the driver query PHYP to
determine if there are any pre-existing mappings... 

Regards, Luke

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