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    SubjectRe: [RFT][PATCH] generic device DMA implementation
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    david-b@pacbell.net said:
    > The indirection is getting from the USB device (or interface) to the
    > object representing the USB controller. All USB calls need that, at
    > least for host-side APIs, since the controller driver is multiplexing
    > up to almost 4000 I/O channels. (127 devices * 31 endpoints, max; and
    > of course typical usage is more like dozens of channels.)

    This sounds like a mirror of the problem of finding the IOMMU on parisc (there
    can be more than one).

    The way parisc solves this is to look in dev->platform_data and if that's null
    walk up the dev->parent until the IOMMU is found and then cache the IOMMU ops
    in the current dev->platform_data. Obviously, you can't use platform_data,
    but you could use driver_data for this. The IOMMU's actually lie on a parisc
    specific bus, so the ability to walk up the device tree without having to know
    the device types was crucial to implementing this.

    James


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