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    SubjectRe: RFC: (re-)binding the VFIO platform driver to a platform device
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    On Wed, 2013-10-02 at 16:40 -0700, gregkh@linuxfoundation.org wrote:
    > On Wed, Oct 02, 2013 at 04:35:15PM -0500, Scott Wood wrote:
    > > On Wed, 2013-10-02 at 14:16 -0700, gregkh@linuxfoundation.org wrote:
    > > > On Wed, Oct 02, 2013 at 04:08:41PM -0500, Scott Wood wrote:
    > > > > I don't see any equivalent functionality to PCI_ANY_ID for platform
    > > > > devices.
    > > >
    > > > Nor should it. If you are wanting to bind platform devices to different
    > > > things based on "ids" or "strings" or something else, then you had
    > > > better not be using a platform device because that is not what you have
    > > > anymore.
    > >
    > > I don't see how anything could be considered a platform device under
    > > your definition.
    >
    > Devices that you just "know" are at a specific memory location ahead of
    > time.
    >
    > > Even before all the device tree stuff came along,
    > > platform devices were still bound based on strings.
    >
    > Not all of them, there are lots that are not, look at ISA devices on a
    > PC platform for one example (your pc speaker, keyboard controller,
    > etc.)

    Using platform devices to let board files provide this information to
    driver files was a big improvement over hacking up the drivers directly
    to know about all sorts of different boards/SoCs. Once you split that
    knowledge into a different place you need a way of matching the two.

    BTW, this is done with the pc speaker as far as I can tell --
    arch/x86/kernel/pcspeaker.c registers a device using the string
    "pcspkr" (as do some non-PC platforms).

    > > And even if we did still have a separate OF platform bus, my point about
    > > there not being a wildcard match applies to of_device_id as well. It
    > > certainly is not the case that "this is already there, and has been for
    > > years with no problems".
    >
    > That's an OF problem then, feel free to fix it there, but not in the
    > driver core with a crazy "ignore this bus type string" hack :)

    Even if we did this for OF and ACPI, you'd still have a problem if you
    want to use VFIO with a platform device that only has plain old
    platform data; thus, the platform bus (not driver core) seems to be the
    appropriate place for a wildcard match if we end up needing it. It may
    be moot though, since for platform devices we may want explicit kernel
    support for a device even with vfio, in order to reset/quiesce it
    between users.

    What it looks like we do still want from the driver core is the ability
    for a driver to say that it should not be bound to a device except via
    explicit sysfs bind, and the ability for a user to say that a device
    should not be bound to a driver except via explicit sysfs bind. This is
    a separate issue from making driver_match_device() happy (in some
    earlier e-mails in the thread these two issues were not properly
    separated).

    -Scott





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