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    SubjectRe: SCSI breakage on non-cache coherent architectures
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    On Mon, 2007-11-19 at 09:09 -0600, James Bottomley wrote:
    > > What other drivers do is DMA to their own allocation and then memcpy to
    > > the sense buffer.
    > >
    > > There is a movement to allocate the sense data as its own sg list, but
    > > I don't think that patch has even been posted yet.
    >
    > I'd like to be rid of it inside the command for various reasons: every
    > command has one of these, and they're expensive in the allocation (at 96
    > bytes). There's no reason we have to allocate and free that amount of
    > space with every command. In theory, the number of these is bounded at
    > the queue depth, in practice, there's usually only one, and this DMA
    > alignment issue does requires most drivers to double copy.

    And most drivers don't and break. Take USB storage, I -think- (code path
    aren't trivial to follow) it just gets the sglist cooked up by the code
    in scsi_error.c no ? That just points to the buffer in scsi_cmnd. It
    then pass that for DMA to the USB stack.

    Ben.


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