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ARM: dma-mapping: Add maximum alignment order for dma iommu buffers

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Alignment order for a dma iommu buffer is set by buffer size. For
large buffer, it is a waste of iommu address space. So configurable
parameter to limit maximum alignment order can reduce the waste.

Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: Kyungmin.park <kyungmin.park@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
This commit is contained in:
Seung-Woo Kim 2013-02-06 13:21:14 +09:00 committed by Marek Szyprowski
parent f8669bef11
commit 60460abffc
2 changed files with 24 additions and 0 deletions
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21
arch/arm/Kconfig
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@ -75,6 +75,27 @@ config ARM_DMA_USE_IOMMU
select ARM_HAS_SG_CHAIN select ARM_HAS_SG_CHAIN
select NEED_SG_DMA_LENGTH select NEED_SG_DMA_LENGTH
if ARM_DMA_USE_IOMMU
config ARM_DMA_IOMMU_ALIGNMENT
int "Maximum PAGE_SIZE order of alignment for DMA IOMMU buffers"
range 4 9
default 8
help
DMA mapping framework by default aligns all buffers to the smallest
PAGE_SIZE order which is greater than or equal to the requested buffer
size. This works well for buffers up to a few hundreds kilobytes, but
for larger buffers it just a waste of address space. Drivers which has
relatively small addressing window (like 64Mib) might run out of
virtual space with just a few allocations.
With this parameter you can specify the maximum PAGE_SIZE order for
DMA IOMMU buffers. Larger buffers will be aligned only to this
specified order. The order is expressed as a power of two multiplied
by the PAGE_SIZE.
endif
config HAVE_PWM config HAVE_PWM
bool bool

3
arch/arm/mm/dma-mapping.c
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@ -1029,6 +1029,9 @@ static inline dma_addr_t __alloc_iova(struct dma_iommu_mapping *mapping,
unsigned int count, start; unsigned int count, start;
unsigned long flags; unsigned long flags;
if (order > CONFIG_ARM_DMA_IOMMU_ALIGNMENT)
order = CONFIG_ARM_DMA_IOMMU_ALIGNMENT;
count = ((PAGE_ALIGN(size) >> PAGE_SHIFT) + count = ((PAGE_ALIGN(size) >> PAGE_SHIFT) +
(1 << mapping->order) - 1) >> mapping->order; (1 << mapping->order) - 1) >> mapping->order;