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Date:   Fri, 16 Nov 2018 01:18:04 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Mika Westerberg <mika.westerberg@linux.intel.com>
Cc:     Yehezkel Bernat <yehezkelshb@gmail.com>, ashok.raj@intel.com,
        Mario Limonciello <Mario.Limonciello@dell.com>,
        michael.jamet@intel.com, Christian Kellner <ckellner@redhat.com>,
        rjw@rjwysocki.net, Anthony Wong <anthony.wong@canonical.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Andreas Noever <andreas.noever@gmail.com>,
        iommu@lists.linux-foundation.org, lukas@wunner.de,
        jacob.jun.pan@intel.com, linux-pci@vger.kernel.org,
        Bjorn Helgaas <bhelgaas@google.com>,
        linux-acpi@vger.kernel.org, David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH 1/4] PCI / ACPI: Identify external PCI devices
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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.

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