linux-kernel - Re: [PATCH 1/4] PCI / ACPI: Identify external PCI devices

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Message-ID: <20181116093210.GK4179@lahna.fi.intel.com>
Date:   Fri, 16 Nov 2018 11:32:10 +0200
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Yehezkel Bernat <yehezkelshb@...il.com>, ashok.raj@...el.com,
        Mario Limonciello <Mario.Limonciello@...l.com>,
        michael.jamet@...el.com, Christian Kellner <ckellner@...hat.com>,
        rjw@...ysocki.net, Anthony Wong <anthony.wong@...onical.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andreas Noever <andreas.noever@...il.com>,
        iommu@...ts.linux-foundation.org, lukas@...ner.de,
        jacob.jun.pan@...el.com, linux-pci@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-acpi@...r.kernel.org, David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 1/4] PCI / ACPI: Identify external PCI devices

On Fri, Nov 16, 2018 at 01:18:04AM -0800, Christoph Hellwig wrote:
> On Thu, Nov 15, 2018 at 09:10:26PM +0200, Mika Westerberg wrote:
> > FireWire is kind of different but there are connectors such as
> > ExpressCard and NVMe (over U.2 connector) which carry PCIe and are
> > relatively easy to access without need for a screwdriver. AFAIK some
> > eGPUs are also using some other proprietary (non-TBT) connector that
> > carries PCIe.
> 
> U.2 is a data center internal form factor with hot plug capability. If
> you enable an iommu for that by default you will make a lot of people
> very unhappy.

Well, it needs the other bit in ACPI DMAR table to be enabled by default
so I don't think anyone in data center domain will notice ;-)

> More importantly NVMe is now used for the current/next generation
> Compact Flash and SD cards, which contain full PCIe gen 3 links.

OK, thanks for the information - I did not know that. I guess those
belong to the "external" category as well.