linux-kernel - Re: [PATCH] pci/iov: VFs are never multifunction

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Date:	Thu, 9 Jan 2014 14:39:00 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	sathya.perla@...lex.com,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	ajit.khaparde@...lex.com, Don Dutile <ddutile@...hat.com>,
	subbu.seetharaman@...lex.com, Myron Stowe <myron.stowe@...hat.com>
Subject: Re: [PATCH] pci/iov: VFs are never multifunction

On Thu, Jan 9, 2014 at 11:25 AM, Alex Williamson
<alex.williamson@...hat.com> wrote:
> On Thu, 2014-01-09 at 11:08 -0700, Bjorn Helgaas wrote:
>> On Thu, Jan 9, 2014 at 8:36 AM, Alex Williamson
>> <alex.williamson@...hat.com> wrote:
>> > Per the SR-IOV spec rev 1.1:
>> >
>> > 3.4.1.9 Header Type (Offset 0Eh)
>> >
>> > "... For VFs, this register must be RO Zero."
>> >
>> > Unfortunately some devices get this wrong, ex. Emulex OneConnect 10Gb
>> > NIC.  When they do it makes us handle ACS testing and therefore IOMMU
>> > groups as if they were actual multifunction devices and require ACS
>> > capabilities to make sure there's no peer-to-peer between functions.
>> > VFs are never traditional multifunction devices, so simply clear this
>> > bit before we get any further into setup.
>>
>> This seems reasonable.  Do you have "lspci -vvxxxx" output for this
>> device?  I'd like to save it for future reference.
>
> Sure, here's a VF:
>
> 09:04.0 Ethernet controller: Emulex Corporation OneConnect 10Gb NIC (be3) (rev 01)
>         Subsystem: Emulex Corporation Device e722

Thanks!  I put this in
https://bugzilla.kernel.org/show_bug.cgi?id=68431, and I'll add a
reference to the changelog.

But I wonder if we can make this slightly more generic by doing
something like this in pci_setup_device():

  dev->multifunction = (PCI_FUNC(dev->devfn) == 0) && (hdr_type & 0x80);

That's basically what lspci does in pci_generic_scan_bus(), and
section 3.2.2.3.4 of the PCI 3.0 spec sort of implies that we should
only look at the bit 7 of the header type for function 0:

  If a single function device is detected (i.e., bit 7 in the Header
  Type register of function 0 is 0), no more functions for that
  Device Number will be checked. If a multi-function device is
  detected (i.e., bit 7 in the Header Type register of function 0
  is 1), then all remaining Function Numbers will be checked.

Bjorn
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