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    SubjectRe: Proposal for new generic device API: dma_get_required_mask()
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    On Fri, 2004-06-18 at 18:07, Krzysztof Halasa wrote:
    > James Bottomley <James.Bottomley@steeleye.com> writes:
    > I don't think so. We already have separate masks for coherent
    > and non-coherent mappings (in PCI API, and I'm told it's to be extended
    > to DMA API as well). And we need them.
    >
    > The problem is we're missing DMA masks for non-alloc calls (depending
    > on the platform) and thus that it isn't very reliable. Drivers which
    > need this are forced to bounce buffers themselves, and many of them
    > will not work on 64-bit platforms (as of ~ 2.6.0, I don't check that
    > regularly). And yes, we really need reliable masks for non-alloc
    > mappings.

    Could you elaborate on this? In the current scheme the coherent mask is
    for descriptor allocation (i.e. dma_alloc_coherent()) and the dma_mask
    represents the bus physical addresses to which the device can DMA
    directly; there's not much more the DMA API really does, what do you
    think is missing?

    James


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