Messages in this thread | | | Date | Tue, 26 Aug 2014 15:00:28 +0200 | From | Marek Szyprowski <> | Subject | Re: [PATCH v2 0/4] CMA & device tree, once again |
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Hello,
On 2014-08-09 02:28, Laura Abbott wrote: > On 7/14/2014 12:12 AM, Marek Szyprowski wrote: >> Hello, >> >> This is one more respin of the patches which add support for creating >> reserved memory regions defined in device tree. The last attempt >> (http://lists.linaro.org/pipermail/linaro-mm-sig/2014-February/003738.html) >> ended in merging only half of the code, so right now we have complete >> documentation merged and only basic code, which implements a half of it >> is written in the documentation. Although the merged patches allow to >> reserve memory, there is no way of using it for devices and drivers. >> >> This situation makes CMA rather useless, as the main architecture (ARM), >> which used it, has been converted from board-file based system >> initialization to device tree. Thus there is no place to use direct >> calls to dma_declare_contiguous() and some new solution, which bases on >> device tree, is urgently needed. >> >> This patch series fixes this issue. It provides two, already widely >> discussed and already present in the kernel, drivers for reserved >> memory: first based on DMA-coherent allocator, second using Contiguous >> Memory Allocator. The first one nicely implements typical 'carved out' >> reserved memory way of allocating contiguous buffers in a kernel-style >> way. The memory is used exclusively by devices assigned to the given >> memory region. The second one allows to reuse reserved memory for >> movable kernel pages (like disk buffers, anonymous memory) and migrates >> it out when device to allocates contiguous memory buffer. Both driver >> provides memory buffers via standard dma-mapping API. >> >> The patches have been rebased on top of latest CMA and mm changes merged >> to akmp kernel tree. >> >> To define a 64MiB CMA region following node is needed: >> >> multimedia_reserved: multimedia_mem_region { >> compatible = "shared-dma-pool"; >> reusable; >> size = <0x4000000>; >> alignment = <0x400000>; >> }; >> >> Similarly, one can define 64MiB region with DMA coherent memory: >> >> multimedia_reserved: multimedia_mem_region { >> compatible = "shared-dma-pool"; >> no-map; >> size = <0x4000000>; >> alignment = <0x400000>; >> }; >> > Longer term, I think it would be good if we didn't have to use no-map with > the coherent memory. With no-map and dma-coherent.c right now, not only > do you lose out on the physical memory space, you also have to give up > the same amount of vmalloc space for mapping. On arm32, if you have the default > 240MB vmalloc space, 64M is ~25% of the vmalloc space. At least on arm you can > make this up by remapping the memory as coherent. > > I haven't seen this picked up anywhere yet so you are welcome to add > > Tested-by: Laura Abbott <lauraa@codeaurora.org>
Right, when the code reaches mainline I will add code which will remove no-map requirement. Changing memory attributes can be handled in this case the same way as for CMA.
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
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