HI, On 2016?06?13? 18:21, Tomasz Figa wrote: > On Mon, Jun 13, 2016 at 6:56 PM, Shunqian Zheng > <shunqian.zheng at gmail.com> wrote: >> Hi >> >> On 2016?06?10? 17:10, Tomasz Figa wrote: >>> Hi, >>> >>> On Wed, Jun 8, 2016 at 10:26 PM, Shunqian Zheng <zhengsq at rock-chips.com> >>> 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? I called dma_alloc_coherent() with DRM device but not the IOMMU device, because DRM didn't attach to any iommu. Even allocating an virtual one when attaching, the iommu->dev is DRM device though. Am I right here? Thank you very much, Shunqian > > Best regards, > Tomasz
