linux-kernel - Re: lspci: Display path to device

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Date:   Tue, 17 Jul 2018 14:46:03 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Martin Mares <mj@....cz>, Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-doc@...r.kernel.org, Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Marc Zyngier <marc.zyngier@....com>,
        Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Christian König <christian.koenig@....com>
Subject: Re: lspci: Display path to device

On Tue, Jul 17, 2018 at 04:00:53PM -0500, Bjorn Helgaas wrote:
> On Tue, Jul 17, 2018 at 01:39:00PM -0700, Matthew Wilcox wrote:
> > The Nehalem system makes an interesting testcase because it exposes some
> > registers in fake PCIe devices that aren't behind the root ports.  eg:
> > 
> > ff:06.3 Host bridge: Intel Corporation Xeon 5500/Core i7 Integrated Memory Controller Channel 2 Thermal Control Registers (rev 04)
> 
> I think these appear as conventional PCI devices; at least the ones
> I've seen, e.g., [1], don't have a PCIe capability, so I think it
> makes sense that they're not behind a root port.
> 
> [1] https://bugzilla5.redhat.com/attachment.cgi?id=433169

Oh, I don't think we're doing anything wrong with how we're displaying
them or what we're doing with what the system presents to us.  My only
point was that this is a good test-case for code which assumes that all
PCI devices lie under a PCIe root port.  At one point during development,
my code reported that device up there as

/06.3 Host bridge: Intel Corporation Xeon 5500/Core i7 Integrated Memory Controller Channel 2 Thermal Control Registers (rev 04)

but since I had that system available to test with, I spotted that problem
and made it present that device as ff:06.3 (both with and without -P).