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    SubjectRe: [PATCH 1/5] dmaengine: add ep93xx DMA support
    On Wed, May 25, 2011 at 10:39:52AM +0200, Linus Walleij wrote:
    > No so much a review comment as an observation: I opposed the merge of the
    > EP93xx SPI driver in drivers/spi/ep93xx_spi.c on the grounds that it was close
    > enough to amba-pl022.c that it could use that driver instead.

    I re-checked the specs and indeed, as discussed previously, it is clear that
    Cirrus (or ARM) copied the interface from other. Even the wording in the
    document is identical in many places. However, in ep93xx User's Guide, there
    is no mention about SSP being AMBA PrimeCell peripheral. For UARTs it is
    mentioned... go figure.

    There are differences also, some of the bits in control registers are in
    different places. Interrupt registers are completely different and there is no
    DMA control register at all. The same things we discussed before.

    > One of the arguments against was that you were going to do custom DMA
    > and stuff. Now you're using the DMAengine, so can you please reconsider
    > refactoring amba-pl022.c to suit your needs and you'll get DMA support for
    > free mor or less.

    Back then, it wasn't known how the M2M DMA interface (the one used by SSP and
    IDE) was going to be implemented. Now that the dmaengine has become de facto
    API, it is clear that any "new" DMA implementations should implement that
    instead of some home grown API. Initially my M2M DMA experiments were just
    like their M2P counterparts but Ryan suggested dmaengine approach.

    IMHO it is better to have ep93xx implementation on its own driver since it is
    not a real AMBA PL022 peripheral but some weird hack made by Cirrus (although
    my opinions are bit biased).


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