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    SubjectRe: [RFC][PATCH] add dma_reserve_coherent_memory()/dma_free_reserved_memory() API
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    On Thu, 26 Aug 2010 10:01:52 +0300
    Marin Mitov <mitov@issp.bas.bg> wrote:

    > > If you add something to the videobuf-dma-contig API, that's fine by me
    > > because drivers/media/video/videobuf-dma-contig.c uses the own
    > > structure and plays with dma_alloc_coherent. As long as a driver
    > > doesn't touch device->dma_mem directly, it's fine,
    >
    > Why, my understanding is that device->dma_mem is designed exactly for keeping
    > some chunk of coherent memory for device's private use via dma_alloc_from_coherent()
    > (and that is what dt3155v4l driver is using it for).

    I don't think so. device->dma_mem can be accessed only via the
    DMA-API. I think that the DMA-API says that
    dma_declare_coherent_memory declares coherent memory that can be
    access exclusively by a certain device. It's not for reserving
    coherent memory that can be used for any device for a device.

    Anway, you don't need coherent memory. So using the API for coherent
    memory isn't a good idea.


    > > There are already some workarounds for
    > > contigous memory in several drivers anyway.
    >
    > Sure, can these workarounds be exposed as API for general use?

    I don't think that's a good idea. Adding temporary workaround to the
    generic API and removing it soon after that doesn't sound a good
    developing maner.


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