linux-kernel - Re: x86/pci/mrst: force all pci config toward 0:0:0, 0:2:0 and 0:3:0 to type 1

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Message-ID: <5187FE55.8080601@zytor.com>
Date:	Mon, 06 May 2013 12:02:45 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Bin Gao <bin.gao@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: x86/pci/mrst: force all pci config toward 0:0:0, 0:2:0 and 0:3:0
 to type 1

On 05/06/2013 10:38 AM, Bjorn Helgaas wrote:
> On Wed, May 1, 2013 at 11:53 PM, Bin Gao <bin.gao@...ux.intel.com> wrote:
>> On Wed, May 01, 2013 at 11:17:10AM -0600, Bjorn Helgaas wrote:
>>> Is there any possibility of multi-function devices at bus 0, device 0, 2, or 3?
>>>
>>> What about bridges -- can any of these be a bridge?
>>>
>>> If either of those could happen, these checks could be too specific.
>> 0:2:0 and 0:3:0 are the only 2 devices behind the bridge 0:0:0.
> 
> Please use the conventional Linux PCI address formatting
> (DDDD:BB:dd.f, where DDDD = domain (optional, often omitted if DDDD ==
> 0), BB = bus, dd = device, f = function), because this is quite
> confusing.
> 
> You say "0:2:0 and 0:3:0" are behind the bridge "0:0:0", but the patch
> you sent clearly applies only to devices on bus 0.  The patch applies
> to devices 00:00.0, 00:02.0, and 00:03.0.  These are all on the same
> bus, so none of them can be behind a bridge.
> 
> If the 00:00.0 device is in fact a bridge, its secondary bus will be
> something other than 0, so any devices behind the bridge will be on a
> non-zero bus number.  And I assume you would want to use config
> mechanism #1 to reach those devices, too.  Your current patch doesn't
> do that -- it only applies to devices on bus 0.
> 

0000:00:00.0 is presumably the *host bridge*, which is unique in PCI
space in that it is a type 0 header and sits on what normally would be
the client bus.

	-hpa
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