On Mon, Jun 13, 2016 at 6:56 PM, Shunqian Zheng <shunqian.zheng@xxxxxxxxx> wrote: > Hi > > On 2016年06月10日 17:10, Tomasz Figa wrote: >> >> Hi, >> >> On Wed, Jun 8, 2016 at 10:26 PM, Shunqian Zheng <zhengsq@xxxxxxxxxxxxxx> >> wrote: >>> >>> Use DMA API instead of architecture internal functions like >>> __cpuc_flush_dcache_area() etc. >>> >>> To support the virtual device like DRM the virtual slave iommu >>> added in the previous patch, attaching to which the DRM can use >>> it own domain->dev for dma_map_*(), dma_sync_*() even VOP is disabled. >>> >>> With this patch, this driver is available for ARM64 like RK3399. >>> >> Could we instead simply allocate coherent memory for page tables using >> dma_alloc_coherent() and skip any flushing on CPU side completely? If >> I'm looking correctly, the driver only reads back the page directory >> when checking if there is a need to allocate new page table, so there >> shouldn't be any significant penalty for disabling the cache. > > I try to use dma_alloc_coherent() to replace the dma_map_single(), > but it doesn't work for me properly. > Because the DRM uses the iommu_dma_ops instead the swiotlb_dma_ops after > attaching > to iommu, so when the iommu domain need to alloc a new page in > rk_iommu_map(), > it would call: > rk_iommu_map() --> dma_alloc_coherent() --> ops->alloc() --> iommu_map() > --> rk_iommu_map() It shouldn't call iommu_map(), because the IOMMU is not behind another IOMMU. Are you sure you called dma_alloc_coherent() on behalf of the IOMMU struct device and not the DRM device? Best regards, Tomasz -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
