linux-kernel - Re: [PATCH] x86/pci: don't use crs for root if we only have one root bus

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Date:	Wed, 24 Jun 2009 17:00:05 -0700
From:	Gary Hade <garyhade@...ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Gary Hade <garyhade@...ibm.com>,
	Matthew Wilcox <matthew@....cx>,
	Larry Finger <Larry.Finger@...inger.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-pci@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jaswinder Singh Rajput <jaswinder@...nel.org>
Subject: Re: [PATCH] x86/pci: don't use crs for root if we only have one
	root bus

On Wed, Jun 24, 2009 at 04:09:36PM -0700, Linus Torvalds wrote:
> 
> Should we not just revert 9e9f46c44e487af0a82eb61b624553e2f7118f5b?
> 
> The thing says:
> 
>  "At this point, it seems to solve more problems than it causes, so let's 
>   try using it by default.  It's an easy revert if it ends up causing 
>   trouble."
> 
> and it clearly does _not_ solve more problems than it causes, and the 
> whole message in that commit implies we should revert it.
> 
> I'm happy to apply various patches to fix it up, but regardless, I thinkwe 
> should revert that commit as bogus. We can try making it the default again 
> next round, when maybe it will be true that it doesn't cause issues.
> 
> What did it even ever help with?

In our case it is needed on some of our systems for PCI hotplug to
avoid MCKs due to a device under one root bus getting a resource
during hotplug that can only be used by devices under a different
root bus.  If the user does not intend to use PCI hotplug, the
function isn't needed (i.e. 'pci=use_crs' can be omitted) because
resources are properly directed to the installed cards via BIOS
pre-assignment.

Gary

-- 
Gary Hade
System x Enablement
IBM Linux Technology Center
503-578-4503  IBM T/L: 775-4503
garyhade@...ibm.com
http://www.ibm.com/linux/ltc

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