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    SubjectRe: DMA changes in 2.3.41 - how the f* do I get this working on ARM?
    On Sun, Jan 30, 2000 at 12:06:15AM +0000, Russell King wrote:
    > Hi,
    > I've been looking over the 2.3.41 patch, and have come across a major problem
    > area for ARM.
    > On ARM, there is no such thing as "dma coherent" memory. Unfortunately, the
    > new PCI code (pci_alloc_consistent) appears to assume that there is a way
    > of doing this.

    Some SPARCs are not DMA coherent either and a similar interface works for
    them for quite some years.
    With the pci_map_single/pci_map_sg/pci_unmap_single/pci_unmap_sg
    you can sync caches in those routines as required (plus there are
    pci_dma_sync_single/pci_dma_sync_sg which should sync as well).
    With pci_alloc_consistant, on DMA non-coherent systems the trick is to
    allocate a non-cacheable memory (or make it uncacheable after allocating).

    > I have had ideas about ways to do this on the ARM, but it will not be trivial
    > changes to the mm layer, and certainly has not been implemented yet.
    > This effectively means that I seem to have two options:
    > 1. either we loose any hope of IDE DMA for the rest of 2.3 and 2.4, or
    > 2. the IDE DMA code gets the dma_cache_* macros added back in
    > I would have preferred to have heard about the extent of these changes (and
    > that the dma_cache_* macros were going to be removed, along with my comments
    > marking them with my initials) before it was submitted.

    The interface was lined out e.g. during the
    Alpha: virt_to_bus/GFP_DMA problem
    thread on l-k in december.

    Jakub Jelinek | |
    Linux version 2.3.41 on a sparc64 machine (1343.49 BogoMips)

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