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: <CAErSpo66x7eHOy3nqH5kgKjOd-176zgNs3EGpJxYrk1dcKPQPg@mail.gmail.com>
Date:	Mon, 6 May 2013 10:38:55 -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 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.

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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