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    SubjectUSB mini-summit at LinuxCon Vancouver
    I'm pleased to announce a USB mini-summit at LinuxCon Vancouver.

    What: USB mini-summit
    When: Tuesday, August 16th, all day
    Where: At the conference venue, room TBD pending confirmation from
    Angela Brown.

    Proposed topics include USB virtualization, and improved bandwidth APIs
    between the USB core and drivers (especially webcam drivers). See the
    detailed topic list below. Anyone is also welcome to propose or show up
    with a USB related topic. MUSB? USB 3.0 gadget drivers? USB-IP?

    The USB mini-summit does overlap with the virtualization mini-summit by
    a day, but I'm hoping we can schedule talks so some of the
    virtualization folks can make it to the USB mini-summit. The other
    option was on Friday during the conference which was not ideal.

    Proposed topics:

    Topic 1
    -------

    The KVM folks suggested that it would be good to get USB and
    virtualization developers together to talk about how to virtualize the
    xHCI host controller. The xHCI spec architect worked closely with
    VMWare to get some extra goodies in the spec to help virtualization, and
    I'd like to see the other virtualization developers take advantage of
    that. I'd also like us to hash out any issues they have been finding in
    the USB core or xHCI driver during the virtualization effort.


    Topic 2
    -------

    I'd also like to get the V4L and audio developers who work with USB
    devices together with the core USB folks to talk about bandwidth
    management under xHCI.

    One of the issues is that since the xHCI hardware does bandwidth
    management, not the xHCI driver, a schedule that will take too much
    bandwidth will get rejected much sooner than any USB driver currently
    expects (during a call to usb_set_interface). This poses issues, since
    most USB video drivers negotiate the video size and frame rate after
    they call usb_set_interface, so they don't know whether they can fall
    back to a less bandwidth-intensive setting. Currently, they just submit
    URBs with less and less bandwidth until one interval setting gets
    accepted that won't work under xHCI.

    A second issue is that that some drivers need less bandwidth than the
    device advertises, and the xHCI driver currently uses whatever periodic
    interval the device advertises in its descriptors. This is not what the
    video/audio driver wants, especially in the case of buggy high speed
    devices that advertise the interval in frames, not microframes. There
    needs to be some way for the drivers to communicate their bandwidth
    needs to the USB core. We've known about this issue for a while, and I
    think it's time to get everyone in the same room and hash out an API.

    (I will send out an API proposal later this month.)

    Hope to see you there!

    Sarah Sharp


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