linux-kernel - Re: [RFC v2 PATCH 1/1] PCI: override BIOS/firmware resource allocation

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Message-Id: <201010221549.22124.bjorn.helgaas@hp.com>
Date:	Fri, 22 Oct 2010 15:49:21 -0600
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Ram Pai <linuxram@...ibm.com>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, clemens@...isch.de,
	Yinghai Lu <yinghai@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC v2 PATCH 1/1] PCI: override BIOS/firmware resource allocation

On Friday, October 22, 2010 12:59:37 pm Ram Pai wrote:
> On Fri, Oct 22, 2010 at 11:55:18AM -0600, Bjorn Helgaas wrote:
> > If we assign resources to bridges with no devices behind them while
> > starving bridges that DO have devices behind them, I think that's a bug.
> > It'd be great if you could isolate and fix that before we complicate
> > things by throwing Yinghai's patch into the mix.
> 
> Yes. I sent out a patch an hour back with a fix for that.

Yeah, I saw that right after I hit "send" :-)

> > I think it'd interesting to have a debug parameter like "pci=assign-all"
> > that meant "ignore all BIOS PCI config and start from scratch."  I'm
> > sure we'd trip over lots of issues and it would be easier to resolve them
> > before trying to make things fancier.
> 
> The patch that I had sent 3-weeks back had that feature. It can be triggered
> by pci=override=always.
> 
> However, your arguement earlier was that it would make no difference because
> no one will enable that parameter by default. This means hardly anyone will
> report any bugs. 

I just meant as a development tool, maybe not even upstream, as a way
to exercise the Linux allocation code.  I don't have much confidence
in it yet.  We certainly don't want Linux to ignore the BIOS config in
general; we should just use it unless we can tell it's broken.

> Gating "Yinghai's patch or any other approach" on fixing all the bugs in the
> pci subsystem, implicitly means 'go away' ;). I hope you dont mean that.

Oh, no.

> I propose to bring Yinghai's patch, for that will enable us to expose bugs and
> at the same time it will enable SRIOV on *all* the platforms that don't have it.

Yes, we should consider Yinghai's patch again after all the known issues
with it are fixed.  I just don't know whether we're there yet.

Bjorn
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