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dma-direct: add support for allocation from ZONE_DMA and ZONE_DMA32 

This allows to dip into zones for lower memory if they are available.
If one of the zones is not available the corresponding GFP_* flag
will evaluate to 0 so they won't change anything.  We provide an
arch tunable for those architectures that do not use GFP_DMA for
the lowest 24-bits, given that there are a few.

Roughly based on the x86 code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
Christoph Hellwig 2018-01-09 23:39:03 +01:00
parent 21f237e4d0
commit c61e963734
1 changed files with 14 additions and 0 deletions
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14
lib/dma-direct.c
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@ -12,6 +12,14 @@
#define DIRECT_MAPPING_ERROR 0
/*
* Most architectures use ZONE_DMA for the first 16 Megabytes, but
* some use it for entirely different regions:
*/
#ifndef ARCH_ZONE_DMA_BITS
#define ARCH_ZONE_DMA_BITS 24
#endif
static bool
check_addr(struct device *dev, dma_addr_t dma_addr, size_t size,
const char *caller)
@ -34,6 +42,12 @@ static void *dma_direct_alloc(struct device *dev, size_t size,
int page_order = get_order(size);
struct page *page = NULL;
/* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
if (dev->coherent_dma_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
gfp |= GFP_DMA;
if (dev->coherent_dma_mask <= DMA_BIT_MASK(32) && !(gfp & GFP_DMA))
gfp |= GFP_DMA32;
/* CMA can be used only in the context which permits sleeping */
if (gfpflags_allow_blocking(gfp))
page = dma_alloc_from_contiguous(dev, count, page_order, gfp);