linux-kernel - Re: [PATCH] x86/pci: intel ioh need to subtract mmconf range

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Message-ID: <20100119194228.GA13570@jgarrett.org>
Date:	Tue, 19 Jan 2010 13:42:28 -0600
From:	jeff@...rrett.org (Jeff Garrett)
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Yinghai Lu <yinghai@...nel.org>,
	Bjorn Helgaas <bjorn.helgaas@...com>,
	linux-kernel@...r.kernel.org, Len Brown <lenb@...nel.org>,
	linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
	David Airlie <airlied@...ux.ie>
Subject: Re: [PATCH] x86/pci: intel ioh need to subtract mmconf range

On Fri, Jan 15, 2010 at 10:14:17AM -0800, Jesse Barnes wrote:
> On Thu, 14 Jan 2010 16:39:13 -0800
> Yinghai Lu <yinghai@...nel.org> wrote:
> 
> > On 01/14/2010 03:49 PM, Bjorn Helgaas wrote:
> > > On Thursday 14 January 2010 04:38:08 pm Yinghai Lu wrote:
> > >> On 01/14/2010 03:09 PM, Bjorn Helgaas wrote:
> > >>> On Thursday 14 January 2010 03:46:35 pm Yinghai Lu wrote:
> > >>>>
> > >>>> Bjorn pointed out we need to remove mmconf range
> > >>>>
> > >>>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> > >>>>
> > >>>> ---
...
> > >>>
> > >>> This can't be right, can it?  Let's say the kernel was built with
> > >>> CONFIG_PCI_MMCONFIG turned off, or the user used "pci=nommconf",
> > >>> or the kernel decides not to use MMCONFIG for some other reason.
> > >>>
> > >>> In that case, the hardware may still be configured to support
> > >>> MMCONFIG, but the pci_mmcfg_list will be empty, so your code will
> > >>> leave the window alone.  We might assign some of that MMCONFIG
> > >>> space to a device, but the hardware will route it to MMCONFIG,
> > >>> not to the device.
> > >>
> > >> so if there is mmconf specified, we just skip the whole function?
> > > 
> > > No, I'm saying that intel-bus.c must ALWAYS remove the MMCONFIG
> > > region from the host bridge apertures, even if Linux isn't using
> > > MMCONFIG.
> > > 
> > > That means intel-bus.c has to be smart enough to figure out on its
> > > own what the MMCONFIG area is.  It can't depend on mmconfig-shared.c
> > > to do it, because mmconfig-shared.c might not be there.
> > 
> > that seems go too far away...
> > 
> > Subject: [PATCH -v2] x86/pci: intel ioh need to subtrac mmconf range
> > 
> > Bjorn pointed out we need to remove mmconf range
> > 
> > -v2: if mmconf is not there, get out early.
> > 
> > Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> > 
> > ---
...
> 
> This goes against the real intent of intel_bus.c doesn't it?  When we
> first added it, the thought was that it would be a purely native way of
> getting at bridge window information and not rely on firmware.  If
> you're going to make it dependent on MMCONFIG now, why not trust other
> firmware tables as well, like _CRS?
> 
> The MMCONFIG ranges are pretty easy to get at, the public docs have
> info about the registers that control the MMCONFIG decode ranges, so
> you should be able to read them out and add them to this file,
> preserving the original intent.

I did attempt a bisection last week, but my pared down config kept
hitting a sysfs_create_file panic.  I didn't succeed.

Should I try the v2 patch above?  What tree is it against?

-Jeff
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