[PATCH v4] arm DMA: Fix allocation from CMA for coherent DMA

On Tue, Jun 30, 2015 at 1:05 PM, Catalin Marinas
[off-list ref] wrote:

On Mon, Jun 29, 2015 at 07:10:45PM +0200, Lorenzo Nava wrote:

quoted

This patch allows the use of CMA for DMA coherent memory allocation.
At the moment if the input parameter "is_coherent" is set to true
the allocation is not made using the CMA, which I think is not the
desired behaviour.

Signed-off-by: Lorenzo Nava <redacted>

It's nice to have a proper email address here.

oops, sorry I thought it was made to avoid spam. This is an easy fix :-)

quoted

@@ -680,9 +684,14 @@ void *arm_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
 static void *arm_coherent_dma_alloc(struct device *dev, size_t size,
      dma_addr_t *handle, gfp_t gfp, struct dma_attrs *attrs)
 {
-     pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL);
+     pgprot_t prot;
      void *memory;

+     if (attrs == NULL)
+              prot  = PAGE_KERNEL;
+     else
+              prot  = __get_dma_pgprot(attrs, PAGE_KERNEL);
+
      if (dma_alloc_from_coherent(dev, size, handle, &memory))
              return memory;

We have a slight inconsistency with commit 55af8a91640d (ARM: 8387/1:
arm/mm/dma-mapping.c: Add arm_coherent_dma_mmap) where the attrs are not
honoured for the coherent ops. That is, DMA_ATTRS_WRITE_COMBINE
doesn't have any effect for mmap but with your patch it still has an
effect on alloc.

I think we could just ignore it, the WRITE_COMBINE attr is a hint that
the arch may or may not implement and I haven't seen it used with
coherent mappings. So in this case just pass PAGE_KERNEL to
__dma_alloc() directly without calling __get_dma_pgprot().

(it also looks like commit 55af8a91640d left an unused attrs argument
for __arm_dma_mmap that can be removed as well)

Right: ok I just pass PAGE_KERNEL to the alloc function, so we are
coherent with the mmap.

Apart from the above, you can add:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

Thanks.