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Date: Mon, 12 Oct 2009 13:49:18 -0700
From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Ingo Molnar <mingo@elte.hu>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>, Yinghai Lu <yinghai@kernel.org>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] x86/pci: intel bus root res with IOH reading -v2
Message-ID: <20091012134918.3246e06b@jbarnes-g45>
In-Reply-To: <20091012203453.GC7648@elte.hu>
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	<200910061133.27546.bjorn.helgaas@hp.com>
	<4ACB839A.2060800@kernel.org>
	<200910061257.54877.bjorn.helgaas@hp.com>
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On Mon, 12 Oct 2009 22:34:53 +0200
Ingo Molnar <mingo@elte.hu> wrote:

> 
> * Bjorn Helgaas <bjorn.helgaas@hp.com> wrote:
> 
> > On Tuesday 06 October 2009 11:51:22 am Yinghai Lu wrote:
> > > Bjorn Helgaas wrote:
> > > > On Sunday 04 October 2009 10:54:24 pm Yinghai Lu wrote:
> > > >> for intel system with multi IOH. we could read peer root
> > > >> resource from PCI conf, and don't trust _CRS again for root bus
> > > > 
> > > > Ugh.  Are we going to end up with amd_bus.c, intel_bus.c,
> > > > nvidia_bus.c, broadcom_bus.c, serverworks_bus.c, etc.?
> > > only needed when you have muti ...
> > 
> > I think that translates to "yes, we will need all those bits as
> > soon as those vendors support larger systems with multiple IOHs."
> > And I think that's the wrong answer.
> 
> Why is having cleanly separated per vendor information/driver wrong?
> I think it's the right answer in most cases. _Especially_ when the
> other option is to 'rely on the firmware'.
> 
> > > again we should trust HW conf than BIOS.
> > 
> > Certainly there's a tradeoff between a generic driver that relies
> > on the BIOS, and a platform-specific driver that uses only the
> > hardware. The first leaves us vulnerable to BIOS bugs, but the
> > second leads to a plethora of drivers that require updates as
> > hardware changes.
> 
> We do that quite well in Linux - it's one of our main strengths.
> 
> Why should we have to rely on correct firmware? Why is it wrong to
> know about the hw's structure, to query the hardware and ignore the
> firmware if the hardware state tells us otherwise?

Right, I think the approaches are complimentary.  We want the hw info,
for cases where the fw is broken or there's no support for a given
configuration, but we also want the fw info for cases where we don't
yet have hw info (e.g. the bridge driver isn't updated) or it isn't
complete.

-- 
Jesse Barnes, Intel Open Source Technology Center
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