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: <CAErSpo4GPMD1kSW7qxBvQmN30NOyx_KruzsFY6SVXkFRMBcDmQ@mail.gmail.com>
Date:	Mon, 6 May 2013 11:56:38 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Bin Gao <bin.gao@...ux.intel.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.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 Mon, May 6, 2013 at 10:38 AM, Bjorn Helgaas <bhelgaas@...gle.com> 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?

I hate it when I go to the trouble of reviewing something and asking
relevant questions, and then people ignore the questions :(

I'd still like to know whether multi-function devices are possible at
bus 0, device 0, 2, or 3.

Are these devices built-in, so you know exactly what they are and they
can never be anything else?  Or is there a slot or other way to
connect a user-chosen device?

>>> 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.

If you included "lspci -vv" output, that would make this much easier
to talk about.

> 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.
>
> I dropped this patch until this gets straightened out.
>
>> These devices don't implement pcie capability list in legacy config space
>> so no offset above 255 would be triggered.
>> The fixed bar pcie capability located at 0x100 is for pci-shimed device
>> only, not for 0, 2 and 3. But current implementation applies it to 0,
>> 2 and 3 as well. This is what the patch is going to address.
>>
>>>
>>> Is there a doc that identifies these cases where config mechanism #1
>>> should be used instead of MMCONFIG?
>> Unfortunately no doc identifies this.
>> But since FW doesn't provide pci shim for device 0, 2 and 3,
>> and these 3 real pci devices have only 256 bytes legacy pci
>> config space so they can only be accessed by type 1.
>>
>>>
>>> Bjorn
>>>
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