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    SubjectRe: DMA mapping on SCSI device?
    --- On Mon, 1/28/08, Robert Hancock <> wrote:
    > The trick is that if an ATAPI device is connected, we (as
    > far as I'm
    > aware) can't use ADMA mode, so we have to switch that
    > port into legacy
    > mode.

    Can you double check this with the HW architect of the
    HW DMA engine of the ASIC?

    > This means it's only capable of 32-bit DMA.
    > However the other port
    > on the controller may be connected to a hard drive and
    > therefore still
    > capable of 64-bit DMA.

    If this is indeed the case as you've presented it here,
    it sounds like a HW shortcoming. I cannot see how the device
    type (or protocol) dictate how the DMA engine operates.
    They live in two different domains.

    > The ideal solution would be to do mapping against a
    > different struct
    > device for each port, so that we could maintain the proper
    > DMA mask for
    > each of them at all times. However I'm not sure if
    > that's possible. The
    > thought of using the SCSI struct device for DMA mapping was
    > brought up
    > at one point.. any thoughts on that?

    The reason for this is that the object that a struct scsi_dev
    represents has nothing to do with HW DMA engines.

    It looks like your current solution is correct and
    x86_64's blk_queue_bounce_limit needs work.


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      Last update: 2008-01-29 23:19    [W:0.019 / U:5.084 seconds]
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