"ARM DMA-Mapping Framework Redesign and IOMMU integration.pdf"
mentioned in this article is here(good to read):
/Files/super119/ARM-DMA-Mapping-Framework-Redesign-and-IOMMU-integration.pdf
Hello eveyone, On Linaro Memory Management meeting in Budapest (May 2011) we have discussed about the design of DMA mapping framework. We tried to identify the drawbacks and limitations as well as to provide some a solution for them. The discussion was mainly about ARM architecture, but some of the conclusions need to be applied to cross-architecture code. The first issue we identified is the fact that on some platform (again, mainly ARM) there are several functions for allocating DMA buffers: dma_alloc_coherent, dma_alloc_writecombine and dma_alloc_noncoherent (not functional now). For each of them there is a match dma_free_* function. This gives us quite a lot of functions in the public API and complicates things when we need to have several different implementations for different devices selected in runtime (if IOMMU controller is available only for a few devices in the system). Also the drivers which use less common variants are less portable because of the lacks of dma_alloc_writecombine on other architectures. The solution we found is to introduce a new public dma mapping functions with additional attributes argument: dma_alloc_attrs and dma_free_attrs(). This way all different kinds of architecture specific buffer mappings can be hidden behind the attributes without the need of creating several versions of dma_alloc_ function. dma_alloc_coherent() can be wrapped on top of new dma_alloc_attrs() with NULL attrs parameter. dma_alloc_writecombine and dma_alloc_noncoherent can be implemented as a simple wrappers which sets attributes to DMA_ATTRS_WRITECOMBINE or DMA_ATTRS_NON_CONSISTENT respectively. These new attributes will be implemented only on the architectures that really support them, the others will simply ignore them defaulting to the dma_alloc_coherent equivalent. The next step in dma mapping framework update is the introduction of dma_mmap/dma_mmap_attrs() function. There are a number of drivers (mainly V4L2 and ALSA) that only exports the DMA buffers to user space. Creating a userspace mapping with correct page attributes is not an easy task for the driver. Also the DMA-mapping framework is the only place where the complete information about the allocated pages is available, especially if the implementation uses IOMMU controller to provide a contiguous buffer in DMA address space which is scattered in physical memory space. Usually these drivers don't touch the buffer data at all, so the mapping in kernel virtual address space is not needed. We can introduce DMA_ATTRIB_NO_KERNEL_MAPPING attribute which lets kernel to skip/ignore creation of kernel virtual mapping. This way we can save previous vmalloc area and simply some mapping operation on a few architectures. This patch series is a preparation for the above changes in the public dma mapping API. The main goal is to modify dma_map_ops structure and let all users to use for implementation of the new public funtions. The proof-of-concept patches for ARM architecture have been already posted a few times and now they are working resonably well. They perform conversion to dma_map_ops based implementation and add support for generic IOMMU-based dma mapping implementation. To get them merged we first need to get acceptance for the changes in the common, cross-architecture structures. More information about these patches can be found in the following threads: http://www.spinics.net/lists/linux-mm/msg19856.html http://www.spinics.net/lists/linux-mm/msg21241.html http://lists.linaro.org/pipermail/linaro-mm-sig/2011-Sept... http://lists.linaro.org/pipermail/linaro-mm-sig/2011-Sept... http://www.spinics.net/lists/linux-mm/msg25490.html The patches are prepared on top of Linux Kernel v3.2-rc6. I would appreciate any comments and help with getting this patch series into linux-next tree. The idea apllied in this patch set have been also presented during the Kernel Summit 2011 and ELC-E 2011 in Prague, in the presentation 'ARM DMA-Mapping Framework Redesign and IOMMU integration'. I'm really sorry if I missed any of the relevant architecture mailing lists. I've did my best to include everyone. Feel free to forward this patchset to all interested developers and maintainers. I've already feel like a nasty spammer. Best regards Marek Szyprowski Samsung Poland R&D Center Patch summary: Andrzej Pietrasiewicz (9): X86: adapt for dma_map_ops changes MIPS: adapt for dma_map_ops changes PowerPC: adapt for dma_map_ops changes IA64: adapt for dma_map_ops changes SPARC: adapt for dma_map_ops changes Alpha: adapt for dma_map_ops changes SH: adapt for dma_map_ops changes Microblaze: adapt for dma_map_ops changes Unicore32: adapt for dma_map_ops changes Marek Szyprowski (5): common: dma-mapping: introduce alloc_attrs and free_attrs methods common: dma-mapping: remove old alloc_coherent and free_coherent methods common: dma-mapping: introduce mmap method common: DMA-mapping: add WRITE_COMBINE attribute common: DMA-mapping: add NON-CONSISTENT attribute Documentation/DMA-attributes.txt | 19 +++++++++++++++++++ arch/alpha/include/asm/dma-mapping.h | 18 ++++++++++++------ arch/alpha/kernel/pci-noop.c | 10 ++++++---- arch/alpha/kernel/pci_iommu.c | 10 ++++++---- arch/ia64/hp/common/sba_iommu.c | 11 ++++++----- arch/ia64/include/asm/dma-mapping.h | 18 ++++++++++++------ arch/ia64/kernel/pci-swiotlb.c | 9 +++++---- arch/ia64/sn/pci/pci_dma.c | 9 +++++---- arch/microblaze/include/asm/dma-mapping.h | 18 ++++++++++++------ arch/microblaze/kernel/dma.c | 10 ++++++---- arch/mips/include/asm/dma-mapping.h | 18 ++++++++++++------ arch/mips/mm/dma-default.c | 8 ++++---- arch/powerpc/include/asm/dma-mapping.h | 24 ++++++++++++++++-------- arch/powerpc/kernel/dma-iommu.c | 10 ++++++---- arch/powerpc/kernel/dma-swiotlb.c | 4 ++-- arch/powerpc/kernel/dma.c | 10 ++++++---- arch/powerpc/kernel/ibmebus.c | 10 ++++++---- arch/powerpc/platforms/cell/iommu.c | 16 +++++++++------- arch/powerpc/platforms/ps3/system-bus.c | 13 +++++++------ arch/sh/include/asm/dma-mapping.h | 28 ++++++++++++++++++---------- arch/sh/kernel/dma-nommu.c | 4 ++-- arch/sh/mm/consistent.c | 6 ++++-- arch/sparc/include/asm/dma-mapping.h | 18 ++++++++++++------ arch/sparc/kernel/iommu.c | 10 ++++++---- arch/sparc/kernel/ioport.c | 18 ++++++++++-------- arch/sparc/kernel/pci_sun4v.c | 9 +++++---- arch/unicore32/include/asm/dma-mapping.h | 18 ++++++++++++------ arch/unicore32/mm/dma-swiotlb.c | 4 ++-- arch/x86/include/asm/dma-mapping.h | 26 ++++++++++++++++---------- arch/x86/kernel/amd_gart_64.c | 11 ++++++----- arch/x86/kernel/pci-calgary_64.c | 9 +++++---- arch/x86/kernel/pci-dma.c | 3 ++- arch/x86/kernel/pci-nommu.c | 6 +++--- arch/x86/kernel/pci-swiotlb.c | 12 +++++++----- arch/x86/xen/pci-swiotlb-xen.c | 4 ++-- drivers/iommu/amd_iommu.c | 10 ++++++---- drivers/iommu/intel-iommu.c | 9 +++++---- drivers/xen/swiotlb-xen.c | 5 +++-- include/linux/dma-attrs.h | 2 ++ include/linux/dma-mapping.h | 13 +++++++++---- include/linux/swiotlb.h | 6 ++++-- include/xen/swiotlb-xen.h | 6 ++++-- lib/swiotlb.c | 5 +++-- 43 files changed, 305 insertions(+), 182 deletions(-)