linux-kernel - Re: [PATCH] pci-hyperv: Use only 16 bit integer for PCI domain

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Date:   Tue, 25 Apr 2017 11:19:13 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Haiyang Zhang <haiyangz@...rosoft.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Piotr Jaroszynski <pjaroszynski@...dia.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "driverdev-devel@...uxdriverproject.org" 
        <driverdev-devel@...uxdriverproject.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pci-hyperv: Use only 16 bit integer for PCI domain

On Tue, 25 Apr 2017, Christoph Hellwig wrote:

> Hi John,
> 
> please fix your quoting of the previous mails, thanks!

Shoot, sorry about any quoting issues. I'm sufficiently new to conversing 
on these lists that I'm not even sure which mistake I made.

> 
> 
> What ACPI defines does not matter at all.  Linux uses 32-bit domains
> IDs, and on x86 specifily uses those for non-ACPI enumarated domains
> (e.g. VMD).
> 
> You've also not demontrated any issue with any Linux driver yet.

The NVIDIA out-of-tree driver has historically treated domains as 16-bit. 
So this showed up when people tried to run that driver in a hyper-v VM.

> 
> > Also...it would be nice if we could use Haiyang's patch as at least a
> > temporary fix, because distros are just today releasing the previous code,
> > and HyperV will start breaking "occasionally", depending on whether the
> > 32-bit virtual (fake) PCI domain fits within 16 bits. (If not, then we can
> > rush out a driver update to fix it, but there will be a window of time with
> > some breakage there.)
> 
> Just send the fix to whatever driver is broken to the driver maintainer.

Done: that would be us. :)

> But I can't find a single broken driver in the tree, and as you know
> nothing else matters for Linux anyway.
> 

Yes, I looked at Nouveau, and I see that they allow for a 32-bit domain, 
so I agree that we haven't found any in-tree drivers that have a problem.

Anyway, thanks for the answers and explanations.

--
thanks,
john h