Hello,
This is a continuation of the dma-mapping extensions posted in the following thread: http://thread.gmane.org/gmane.linux.kernel.mm/78644
We noticed that some advanced buffer sharing use cases usually require creating a dma mapping for the same memory buffer for more than one device. Usually also such buffer is never touched with CPU, so the data are processed by the devices.
From the DMA-mapping perspective this requires to call one of the
dma_map_{page,single,sg} function for the given memory buffer a few times, for each of the devices. Each dma_map_* call performs CPU cache synchronization, what might be a time consuming operation, especially when the buffers are large. We would like to avoid any useless and time consuming operations, so that was the main reason for introducing another attribute for DMA-mapping subsystem: DMA_ATTR_SKIP_CPU_SYNC, which lets dma-mapping core to skip CPU cache synchronization in certain cases.
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. I will resend them rebased onto v3.5-rc1 soon.
Best regards Marek Szyprowski Samsung Poland R&D Center
Patch summary:
Marek Szyprowski (2): common: DMA-mapping: add DMA_ATTR_SKIP_CPU_SYNC attribute ARM: dma-mapping: add support for DMA_ATTR_SKIP_CPU_SYNC attribute
Documentation/DMA-attributes.txt | 24 ++++++++++++++++++++++++ arch/arm/mm/dma-mapping.c | 20 +++++++++++--------- include/linux/dma-attrs.h | 1 + 3 files changed, 36 insertions(+), 9 deletions(-)