linux-kernel - Re: [RFC PATCH 1/1] PCI: skip release and reallocation of io port resources

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Message-ID: <20100709082506.514f64ab@virtuousgeek.org>
Date:	Fri, 9 Jul 2010 08:25:06 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ram Pai <linuxram@...ibm.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, clemens@...isch.de
Subject: Re: [RFC PATCH 1/1] PCI: skip release and reallocation of io port 
 resources

On Tue, 06 Jul 2010 17:49:32 -0700
Yinghai Lu <yinghai@...nel.org> wrote:

> On 07/06/2010 04:58 PM, Linus Torvalds wrote:
> > On Tue, Jul 6, 2010 at 4:13 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> >>
> >> So you want to use pci=override_bios to reallocate all bios assigned resource include
> >> peer root buses resources and pci bridge resource and pci devices BAR?
> > 
> > In a perfect world, we'd never need this at all, but sicne that's not
> > an option, the second-best alternative might be something like the
> > following:
> > 
> >   pci=override=off # default
> >   pci=override=conflict # override only on conflicts
> >   pci=override=<device> # clear BIOS allocations for <device> (and any
> > children, if it's a bus)
> 
> current:
> if there is conflict, like pci bridge resources or pci devices resources is not in the scope of peer root bus resource range.
> or pci devices is not in pci bridge resources range.
> kernel would reject the resource and try to get new range in parent resource for the children.
> 
> so current default is overriding the conflicts already.
> 
> Maybe your conflicts have other meaning? like pci bridge resource size is not big enough?
> 
> or we can have use
> 
> pci=override=small_bridge
> 
> or 
> 
> pci=override=bridges
> 
> instead?

Changing the default (and fairly old) behavior at this point will
probably cause a lot of trouble; we have machines where reallocating
conflicting or apparently mis-programmed resources is needed.

But we can still add the pci=override= option.  Your patch will need
some changes though; a user needing a specific bus/bridge reallocated
can just pass the bridge id.  And rather than walking its way up,
freeing and trying to re-allocate, it could just free everything below
the given device and let the normal paths allocate it.

-- 
Jesse Barnes, Intel Open Source Technology Center
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