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    SubjectRe: [PATCH 07/11] spi/pxa2xx: add support for DMA engine
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    On Mon, Jan 7, 2013 at 11:44 AM, Mika Westerberg
    <mika.westerberg@linux.intel.com> wrote:

    > In order to use DMA with this driver on non-PXA platforms we implement support
    > for the generic DMA engine API. This allows to use different DMA engines with
    > little or no modification to the driver.
    >
    > Request lines and channel numbers can be passed to the driver from the
    > platform specific data.
    >
    > Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
    > ---
    > drivers/spi/spi-pxa2xx.c | 351 +++++++++++++++++++++++++++++++++++++++-
    > include/linux/spi/pxa2xx_spi.h | 6 +

    So if the other DMA implementation could go into spi-pxa2xx-pxadma.c
    this could be spi-pxa2xx-dma.c and they could use the common header
    file spi-pxa2xx-dma.h and then Kconfig select which one to compile.

    Just a suggestion to get the driver more readable.

    > + /*
    > + * Some DMA controllers have problems transferring buffers that are
    > + * not multiple of 4 bytes. So we truncate the transfer so that it
    > + * is suitable for such controllers, and handle the trailing bytes
    > + * manually after the DMA completes.
    > + */
    > + len = ALIGN(drv_data->len, 4);

    This is actually a property of the DMA controller.

    struct dma_device already has this:

    * @copy_align: alignment shift for memcpy operations
    * @xor_align: alignment shift for xor operations
    * @pq_align: alignment shift for pq operations
    * @fill_align: alignment shift for memset operations
    (...)
    u8 copy_align;
    u8 xor_align;
    u8 pq_align;
    u8 fill_align;

    To align memcpy's on 4 bytes you can e.g. set .copy_align
    to 2.

    So the syntax is number of shifts 1 << 2 = 4.

    If slave transfers can expose the same type of property we should
    maybe introdyce .slave_align in the same manner so you don't have
    to assume the worst in the driver.

    Vinod/Dan? What do you say about this?

    Yours,
    Linus Walleij


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