Re: [PATCH 7/8] common: dma-mapping: change alloc/free_coherent method to more generic alloc/free_attrs

[Arnd Bergmann <arnd@arndb.de>]

On Monday 20 June 2011, Marek Szyprowski wrote:
> Introduce new alloc/free/mmap methods that take attributes argument.
> alloc/free_coherent can be implemented on top of the new alloc/free
> calls with NULL attributes. dma_alloc_non_coherent can be implemented
> using DMA_ATTR_NONCOHERENT attribute, dma_alloc_writecombine can also
> use separate DMA_ATTR_WRITECOMBINE attribute. This way the drivers will
> get more generic, platform independent way of allocating dma memory
> buffers with specific parameters.
> 
> One more attribute can be usefull: DMA_ATTR_NOKERNELVADDR. Buffers with
> such attribute will not have valid kernel virtual address. They might be
> usefull for drivers that only exports the DMA buffers to userspace (like
> for example V4L2 or ALSA).
> 
> mmap method is introduced to let the drivers create a user space mapping
> for a DMA buffer in generic, architecture independent way.
> 
> TODO: update all dma_map_ops clients for all architectures
> 
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>

Yes, I think that is good, but the change needs to be done atomically
across all architectures. This should be easy enough as I believe
all other architectures that use dma_map_ops don't even require
dma_alloc_noncoherent but just define it to dma_alloc_coherent
because they have only coherent memory in regular device drivers.

On a related note, do you plan to make the CMA work use this
transparently, or do you want to have a DMA_ATTR_LARGE or
DMA_ATTR_CONTIGUOUS for CMA?

	Arnd

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