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CONFIG_ARM_DMA_IOMMU_ALIGNMENT: Maximum PAGE_SIZE order of alignment for DMA IOMMU buffers

General informations

The Linux kernel configuration item CONFIG_ARM_DMA_IOMMU_ALIGNMENT:

Help text

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.



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