linux-kernel - Re: [PATCH] PCI: Support SRIOV on Legacy EndPoint device

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Date:	Fri, 5 Feb 2016 10:59:55 -0600
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	"Zytaruk, Kelly" <Kelly.Zytaruk@....com>
Cc:	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Yu Zhao <yuzhao@...gle.com>
Subject: Re: [PATCH] PCI: Support SRIOV on Legacy EndPoint device

On Fri, Feb 05, 2016 at 04:50:11PM +0000, Zytaruk, Kelly wrote:
> 
> 
> > -----Original Message-----
> > From: Bjorn Helgaas [mailto:helgaas@...nel.org]
> > Sent: Friday, February 05, 2016 11:47 AM
> > To: Zytaruk, Kelly
> > Cc: bhelgaas@...gle.com; linux-pci@...r.kernel.org; linux-
> > kernel@...r.kernel.org; Alex Williamson; Yu Zhao
> > Subject: Re: [PATCH] PCI: Support SRIOV on Legacy EndPoint device
> > 
> > On Thu, Feb 04, 2016 at 04:21:08PM +0000, Zytaruk, Kelly wrote:
> > > > -----Original Message-----
> > > > From: Bjorn Helgaas [mailto:helgaas@...nel.org]
> > > > Sent: Thursday, February 04, 2016 10:14 AM
> > > > To: Zytaruk, Kelly
> > > > Cc: bhelgaas@...gle.com; linux-pci@...r.kernel.org; linux-
> > > > kernel@...r.kernel.org; Alex Williamson; Yu Zhao
> > > > Subject: Re: [PATCH] PCI: Support SRIOV on Legacy EndPoint device
> > > >
> > > > [+cc Alex, Yu (participants in previous discussion)]
> > > >
> > > > Hi Kelly,
> > > >
> > > > On Thu, Feb 04, 2016 at 09:48:26AM -0500, Kelly Zytaruk wrote:
> > > > > Some AMD GPUs have hardware support for grapics SRIOV.
> > > > > If the GPU has a display output then the GPU needs to support
> > > > > Legacy VGA
> > > > operation.
> > > > > If CLASS_CODE = VGA then the device should have a Port Type =
> > > > > Legacy
> > > > EndPoint.
> > > > > Therefore in order to enable SRIOV on a GPU with a display output
> > > > LEGACY_END_POINT is supported as a valid Port Type.
> > > > >
> > > > > Signed-off-by: Kelly Zytaruk <kelly.zytaruk@....com>
> > > >
> > > > We had an interesting discussion about this two years ago:
> > > >
> > http://lkml.kernel.org/r/B756807489D6244883AC0B799A6EEC15EAB2E8@stor
> > > > e
> > > > xdag02.amd.com
> > >
> > > Unfortunately 2 years ago I couldn't complete your request as it would
> > > have disclosed Information about an unannounced technology that we
> > > were working on.  We have recently made that technology public and I
> > > can now send you the requested information.
> > 
> > > > Please include a reference to that discussion in your changelog.  In
> > > > that discussion, I also asked for some details (dmesg and lspci
> > > > info) that motivate the change, so please collect and add a reference to
> > them as well.
> > >
> > > The information that you ask for is included below.  I have
> > > abbreviated it so that this does not become a huge email.  I can send
> > > full logs if you want them.
> > 
> > Can you open a bugzilla at http://bugzilla.kernel.org and attach the full logs
> > there?  Then we can include the URL in your patch changelog.
> 
> I have never worked with bugzilla before but I will check it out.  So you
> want me to take the bugzilla URL and paste it into the comments of my
> patch? Or is this something that you will do?

Put it in the bugzilla drivers/PCI category.  Let me know if you have
any bugzilla troubles.  It should be pretty self-explanatory.  Please
attach the files rather than pasting them in the text box.

If you could include the bugzilla URL in the changelog of a revised
patch, that would be great.  

> > > > It's not clear to me why we check the device type at all.  If
> > > > there's no spec restriction on the types of devices that can have an
> > > > SR-IOV capability, we should consider removing the test altogether
> > > > (Alex mentioned this possiblity in the earlier discussion).
> > >
> > > I am as well not clear why the check is in there.  I would be just as
> > > happy either adding TYPE_LEG_END or removing the check all together.
> > > I don't know what the side effects of removing the check would be. I
> > > don't have any sriov devices other than a graphics card to test with
> > > so I wouldn't be able to test other scenarios.
> > 
> > If we don't have a reason to do the check, I think we should just remove it
> > altogether.
> 
> So instead of my proposed change do you want me to just remove the check
> completely and submit a patch for that?

Please.

Bjorn