Hello,
This patch series introduces a new features to DMA mapping subsystem to let drivers share the allocated buffers (preferably using recently introduced dma_buf framework) easy and efficient.
The first extension is DMA_ATTR_NO_KERNEL_MAPPING attribute. It is intended for use with dma_{alloc, mmap, free}_attrs functions. It can be used to notify dma-mapping core that the driver will not use kernel mapping for the allocated buffer at all, so the core can skip creating it. This saves precious kernel virtual address space. Such buffer can be accessed from userspace, after calling dma_mmap_attrs() for it (a typical use case for multimedia buffers). The value returned by dma_alloc_attrs() with this attribute should be considered as a DMA cookie, which needs to be passed to dma_mmap_attrs() and dma_free_attrs() funtions.
The second extension is required to let drivers to share the buffers allocated by DMA-mapping subsystem. Right now the driver gets a dma address of the allocated buffer and the kernel virtual mapping for it. If it wants to share it with other device (= map into its dma address space) it usually hacks around kernel virtual addresses to get pointers to pages or assumes that both devices share the DMA address space. Both solutions are just hacks for the special cases, which should be avoided in the final version of buffer sharing. To solve this issue in a generic way, a new call to DMA mapping has been introduced - dma_get_sgtable(). It allocates a scatter-list which describes the allocated buffer and lets the driver(s) to use it with other device(s) by calling dma_map_sg() on it.
The proposed patches have been generated on top of the ARM DMA-mapping redesign patch series on Linux v3.4-rc7. They are also available on the following GIT branch:
git://git.linaro.org/people/mszyprowski/linux-dma-mapping.git 3.4-rc7-arm-dma-v10-ext
with all require patches on top of vanilla v3.4-rc7 kernel.
Best regards Marek Szyprowski Samsung Poland R&D Center
Patch summary:
Marek Szyprowski (3): common: DMA-mapping: add DMA_ATTR_NO_KERNEL_MAPPING attribute ARM: dma-mapping: add support for DMA_ATTR_NO_KERNEL_MAPPING attribute ARM: dma-mapping: add support for dma_get_sgtable()
Documentation/DMA-attributes.txt | 18 +++++++++++++ arch/arm/include/asm/dma-mapping.h | 12 +++++++++ arch/arm/mm/dma-mapping.c | 51 ++++++++++++++++++++++++++++++++---- include/linux/dma-attrs.h | 1 + include/linux/dma-mapping.h | 3 +++ 5 files changed, 80 insertions(+), 5 deletions(-)