On Wednesday 19 November 2014 11:17:15 Ding Tianhong wrote: > On 2014/11/18 2:09, Catalin Marinas wrote: > > On Mon, Nov 17, 2014 at 12:18:42PM +0000, Arnd Bergmann wrote: > >> On Monday 17 November 2014 19:56:27 Ding Tianhong wrote: > >>> The commit 3690951fc6d42f3a0903987677d0e592c49dd8db(arm64: Use > >>> swiotlb late initialisation) > >>> switches the DMA mapping code to > >>> swiotlb_tlb_late_init_with_default_size(), this will occur a problem > >>> when I run the scsi stress tests, the message as below: > >>> > >>> sas_controller b1000000.sas: swiotlb buffer is full (sz: 65536 > >>> bytes).. > >>> DMA: Out of SW-IOMMU space for 65536 bytes at device b1000000.sas > >>> > >>> The reason is that the swiotlb_tlb_late_init_with_default_size() could > >>> only alloc 16M memory for DMA-mapping, > >>> and the param in cmdline "swiotlb=xxx" is useless because the > >>> get_free_pages() only use the buddy to assigned a > >>> maximum memory of 16M(The MAX_ORDER is 13 for 4k pages), obviously 16M is > >>> too small in many scenes, but > >>> the swiotlb_init() which could reserved a bigger memory as wished could > >>> work well for most drivers. > >>> > >>> I could not get a better way to fix this problem except to revert this > >>> patch, so could you please give me some > >>> advise and help me, thanks very much. > >> > >> In general, you should not need to use swiotlb for most devices, in > >> particular for high-performance devices like network or block. > >> > >> Please make sure that you have set up the dma-ranges properties in > >> your DT properly to allow 64-bit DMA if the device supports it. > > > > That's the problem indeed, the DMA API ends up using swiotlb bounce > > buffers because the physical address of the pages passed to (or > > allocated by) the driver are beyond 32-bit limit (which is the default > > dma mask). > > > > Thanks everyone, I think I found the way to fix it, need to enable DMA_CMA, > to reserve a big memory > for CMA and set coherent mask for dev, then dma_alloc and dma_mapping will > not use the swiotlb until > the memory out of mask or swiotlb_force is enabled. > > If I still understand uncorrectly, please inform me. >
Please do not use CMA to work around the problem, but fix the underlying bug instead. The driver should call 'dma_set_mask_and_coherent()' with the appropriate dma mask, and check whether that succeeded. However, the code implementing dma_set_mask_and_coherent on arm64 also needs to be changed to look up the dma-ranges property (see of_dma_configure()), and check if the mask is possible. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/