On Mon, Jun 13, 2016 at 7:31 PM, Shunqian Zheng <shunqian.zheng at gmail.com> wrote: > HI, > > > On 2016å¹´06æ13æ¥ 18:21, Tomasz Figa wrote: >> >> On Mon, Jun 13, 2016 at 6:56 PM, Shunqian Zheng >> <shunqian.zheng at gmail.com> wrote: >>> >>> Hi >>> >>> On 2016å¹´06æ10æ¥ 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?
What I meant, is that even though rk_iommu_map() is called for DRM device, the page table allocation happening inside should be called for the IOMMU device itself, because it's the consumer of these page tables. Best regards, Tomasz
