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    SubjectRe: USB mass storage and ARM cache coherency
    On Thu, 25 Feb 2010, Benjamin Herrenschmidt wrote:

    > I'm surprised that usb-storage has an issue here. It shouldn't afaik,
    > since it's just a SCSI driver (or not anymore ?)

    It still is. There's also the ub driver, which is a non-SCSI block
    device driver for some of the same devices handled by usb-storage.

    > and the BIO or
    > filesystems handle things there no ? I haven't seen a single call to
    > flush_dcache_page() in any of drivers/scsi, drivers/ata or drivers/ide
    > when I looked...

    There is no real issue; it's just that the problem was first noted in
    connection with usb-storage reading in executable pages, so Catalin's
    initial post was oriented toward modifying usb-storage.

    The main issue here is that the same host controller will use PIO
    sometimes and DMA sometimes, depending on the details of the transfer.
    The USB core didn't expect this and consequently we violated the rules
    for DMA mapping. The question is: If the core is fixed so that the
    rules aren't violated, will everything work correctly?

    Alan Stern



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