linux-kernel - Re: [Bug #15124] PCI host bridge windows ignored (works with pci=use

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Date:	Wed, 27 Jan 2010 21:26:02 -0700
From:	Bjorn Helgaas <bjorn.helgaas@...com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Jeff Garrett <jeff@...rrett.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Linux PCI <linux-pci@...r.kernel.org>,
	Myron Stowe <myron.stowe@...com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [Bug #15124] PCI host bridge windows ignored (works with
	pci=use_crs)

On Wed, 2010-01-27 at 15:34 -0800, Yinghai Lu wrote:
> On 01/27/2010 01:03 PM, Bjorn Helgaas wrote:
> > On Wednesday 27 January 2010 01:50:12 pm Linus Torvalds wrote:
> >>
> >> On Wed, 27 Jan 2010, Bjorn Helgaas wrote:
> >>>
> >>> Without intel_bus.c, we essentially assume config 1 all the time.
> >>> If we keep intel_bus.c and this patch for .33, things should work
> >>> for configs 1 and 4.  Adding support for config 4 is good.
> >>
> >> Quite frankly, is there any major downside to just disabling/removing 
> >> intel_bus.c for 2.6.33? If we're not planning on having it in the long run 
> >> anyway - or even if we are, but we can't be really happy about the state 
> >> of it as it would be in 2.6.33, not using it at all seems to be the 
> >> smaller headache.
> >>
> >> The machines that it helps are also the machines where you can fix things 
> >> up with 'use_csr', no? And they are pretty rare, and they didn't use to 
> >> work without that use_csr in 2.6.32 either, so it's not even a regression.
> >>
> >> Am I missing something?
> > 
> > Only that when we added intel_bus.c, Yinghai reported that the reason
> > was because a machine had a broken _CRS, so "pci=use_crs" wouldn't help.
> > 
> > At the time, Windows hadn't been brought up on that box.  My
> > speculation is that by now, they've done that bringup and probably
> > fixed the _CRS issue, so it might work now.
> > 
> > If that's the case, we could drop intel_bus.c from .33 and just use
> > "pci=use_crs" on those boxes until we can figure out how to turn it
> > on automatically.
> 
> BIOS fixed that problem already. but
> 1. how to turn that pci=use_crs for that box automatically ?
> how about our other kind of boxes?

Yes, we need a way to turn on "pci=use_crs" automatically.  My first
thought is to turn it on for all BIOSes with dates of 2010 or later, and
in addition, have a whitelist of the pre-2010 machines that require it.

> 2. how about when apci is disabled?

When ACPI is disabled, I think we just have to accept that we lose some
functionality.  I don't see the need for alternate ways to accomplish
everything that ACPI does.  It's becoming less and less useful to
disable ACPI; I think it's only interesting as a debugging tool, and
even then it's a sledgehammer.

Bjorn


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