linux-kernel - Re: [PATCH 4/8] PCI: Add quirk to disable MSI support for Amazon's Annapurna Labs host bridge

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Date:   Mon, 15 Jul 2019 08:54:00 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     "Chocron, Jonathan" <jonnyc@...zon.com>,
        "helgaas@...nel.org" <helgaas@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "Woodhouse, David" <dwmw@...zon.co.uk>,
        "Hanoch, Uri" <hanochu@...zon.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "gustavo.pimentel@...opsys.com" <gustavo.pimentel@...opsys.com>,
        "Wasserstrom, Barak" <barakw@...zon.com>,
        "Saidi, Ali" <alisaidi@...zon.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "Hawa, Hanna" <hhhawa@...zon.com>,
        "Shenhar, Talel" <talel@...zon.com>,
        "Krupnik, Ronen" <ronenk@...zon.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH 4/8] PCI: Add quirk to disable MSI support for Amazon's
 Annapurna Labs host bridge

On Sun, 2019-07-14 at 15:09 +0000, Chocron, Jonathan wrote:
> > s/host bridge/Root Port/, if I understand correctly.
> > 
> 
> Ack.
> 
> BTW, what is the main difference between the 2 terms, since they seem
> to be (mistakenly?) used interchangeably?

The host bridge is the parent of the root port. You can have several
root ports under a host bridge in fact. They tend to be part of the
same silicon and somewhat intimately linked but they are distinct
logical entities. The root port appears as a PCIe p2p bridge sitting on
the top level bus provided by the host bridge. The Host Bridge doesn't
have to have a representation in config space (it sometimes does
historically, but as a sibling of the devices on that top level bus. In
PCIe land, these are chipset built-in devices).

Ben.