HI,
On 2016年06月13日 18:21, Tomasz Figa wrote:
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?
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
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