Eric Lee / smarc-fsl-linux-kernel

06 Jan, 2009

1 commit

  • 28405d8d9   async_tx, dmaengine: document channel allocation and api rework ... Browse Code ยป

    "Wouldn't it be better if the dmaengine layer made sure it didn't pass
    the same channel several times to a client?

    I mean, you seem concerned that the memcpy() API should be transparent
    and easy to use, but the whole registration interface is just
    ridiculously complicated..."
    - Haavard

    The dmaengine and async_tx registration/allocation interface is indeed
    needlessly complicated. This redesign has the following goals:

    1/ Simplify reference counting: dma channels are not something one would
    expect to be hotplugged, it should be an exceptional event handled by
    drivers not something clients should be mandated to handle in a
    callback. The common case channel removal event is 'rmmod ',
    which for simplicity should be disallowed if the channel is in use.
    2/ Add an interface for requesting exclusive access to a channel
    suitable to device-to-memory users.
    3/ Convert all memory-to-memory users over to a common allocator, the goal
    here is to not have competing channel allocation schemes. The only
    competition should be between device-to-memory exclusive allocations and
    the memory-to-memory usage case where channels are shared between
    multiple "clients".

    Cc: Haavard Skinnemoen
    Cc: Neil Brown
    Cc: Jeff Garzik
    Reviewed-by: Andrew Morton
    Signed-off-by: Dan Williams

    Dan Williams