linux-kernel - Re: [PATCH] x86/pci: do assign root bus res if

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Message-ID: <20090611110035.209122a4@jbarnes-g45>
Date:	Thu, 11 Jun 2009 11:00:35 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Gary Hade <garyhade@...ibm.com>
Cc:	Gary Hade <garyhade@...ibm.com>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	Yinghai Lu <yhlu.kernel@...il.com>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org, Alex Chiang <achiang@...com>,
	linux-acpi@...r.kernel.org, Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH] x86/pci: do assign root bus res if _CRS is used

On Wed, 27 May 2009 12:41:44 -0700
Gary Hade <garyhade@...ibm.com> wrote:

> On Thu, May 21, 2009 at 09:37:37AM -0700, Gary Hade wrote:
> > On Thu, May 21, 2009 at 08:46:17AM -0600, Bjorn Helgaas wrote:
> > > On Wednesday 20 May 2009 5:49:10 pm Jesse Barnes wrote:
> > > > On Fri, 8 May 2009 16:40:10 -0600
> > > > Bjorn Helgaas <bjorn.helgaas@...com> wrote:
> > > > > Did anything happen with this?
> > > > > 
> > > > > The longer we wait to make "use_crs" the default, the harder
> > > > > it will be, so I'd like to push ahead.
> > > > 
> > > > Here's a patch to make CRS the default.  If it looks ok I can
> > > > push it into my linux-next branch.  I'm all for using reliable
> > > > data from the BIOS.  I guess we'll find out fairly quickly if
> > > > this stuff isn't...
> > > 
> > > Thanks for following up on this, Jesse.  It was on my to-do list
> > > for yesterday, but I didn't get to it.
> > > 
> > > Yinghai mentioned a specific box where we might have trouble, but
> > > we never got enough details to really debug it.  So I think we
> > > might as well give it a shot and fine-tune it as we need to.
> > 
> > I just remembered that Andrew Morton once raised some concerns
> > related to the number of _CRS returned resources exceeding the
> > fixed resource array size -> http://lkml.org/lkml/2007/11/1/49
> > 
> > I believe PCI_BUS_NUM_RESOURCES was later increased but if 
> > that increase was insufficient to cover all systems that the
> > code will now be exposed to, it seems like the "And should we
> > really be silently ignoring this problem?  Should we at least
> > report it?" comment that was not addressed could become relevent.
> 
> Not only do we not warn, if we did warn based on the current
>     'if (info->res_num >= PCI_BUS_NUM_RESOURCES)'
> resource array overrun avoidance criteria it would be incorrect
> for a root bus that is connected to a subordinate bus with a
> transparent bridge.  We need to avoid the last 3 slots of the
> resource array since they do not get mapped to a transparent
> bridge connected subordinate bus.  I believe the below patch
> addresses these issues.
> 
> With PCI_BUS_NUM_RESOURCES currently at 16 we still have space
> to accomodate 13 _CRS returned resource descriptors which will
> hopefully be sufficient.

Ok, applied the patch (with Yinghai's suggested name change) to my
linux-next branch.  We'll see now it goes and revert it if there's
trouble.


-- 
Jesse Barnes, Intel Open Source Technology Center
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