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

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>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 67874b8..4e89112 100644 (file)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -75,6 +75,27 @@ config ARM_DMA_USE_IOMMU
        select ARM_HAS_SG_CHAIN
        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
        bool
 

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 2163af4..6e25115 100644 (file)
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -1029,6 +1029,9 @@ static inline dma_addr_t __alloc_iova(struct dma_iommu_mapping *mapping,
        unsigned int count, start;
        unsigned long flags;
 
+       if (order > CONFIG_ARM_DMA_IOMMU_ALIGNMENT)
+               order = CONFIG_ARM_DMA_IOMMU_ALIGNMENT;
+
        count = ((PAGE_ALIGN(size) >> PAGE_SHIFT) +
                 (1 << mapping->order) - 1) >> mapping->order;