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Date:   Wed, 18 Nov 2020 15:05:16 -0600
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Guilherme Piccoli <gpiccoli@canonical.com>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        Thomas Gleixner <tglx@linutronix.de>, lukas@wunner.de,
        linux-pci@vger.kernel.org, Pingfan Liu <kernelfans@gmail.com>,
        andi@firstfloor.org, "H. Peter Anvin" <hpa@zytor.com>,
        Baoquan He <bhe@redhat.com>, x86@kernel.org,
        Sinan Kaya <okaya@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Jay Vosburgh <jay.vosburgh@canonical.com>,
        Dave Young <dyoung@redhat.com>,
        Gavin Guo <gavin.guo@canonical.com>,
        Borislav Petkov <bp@alien8.de>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Guowen Shan <gshan@redhat.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        "Guilherme G. Piccoli" <kernel@gpiccoli.net>,
        kexec mailing list <kexec@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Dan Streetman <ddstreet@canonical.com>,
        Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [PATCH 1/3] x86/quirks: Scan all busses for early PCI quirks
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On Tue, Nov 17, 2020 at 09:04:07AM -0300, Guilherme Piccoli wrote:

> Also, taking here the opportunity to clarify my understanding about
> the limitations of that approach: Bjorn, in our reproducer machine we
> had 3 parents in the PCI tree (as per lspci -t), 0000:00, 0000:ff and
> 0000:80 - are those all under "segment 0" as per your verbiage?

Yes.  The "0000" is the PCI segment (or "domain" in the Linux PCI core).
It's common on x86 to have multiple host bridges in segment 0000.