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