Re: [PATCH v5 4/7] drivers: dma-coherent: Introduce default DMA pool

[Christoph Hellwig]

On Wed, May 24, 2017 at 11:24:29AM +0100, Vladimir Murzin wrote:
> This patch introduces default coherent DMA pool similar to default CMA
> area concept. To keep other users safe code kept under CONFIG_ARM.

I don't see a CONFIG_ARM in the code, although parts of it are added
under CONFIG_OF_RESERVED_MEM.

But overall this code look a bit odd to me.  As far as I can tell
the dma-coherent.c code is for the case where we have a special
piece of coherent memory close to a device.

If you're allocating out of the global allocator the memory should
come from the normal dma_ops ->alloc allocator - and also take
the attrs into account (e.g. for DMA_ATTR_NON_CONSISTENT or
DMA_ATTR_NO_KERNEL_MAPPING requests you don't need coherent memory)