Hi, According to the CPU access instructions in the dma-buf.c, I understand that on 32 bit platforms, due to the limited number of persistent kernel mappings or limited vmalloc range, the CPU access pattern should look like this: dma_buf_start_cpu_access(); void *ptr = dma_buf_kmap(); /*Access the page pointed by ptr*/ dma_buf_kunmap(ptr); dma_buf_end_cpu_access(); or dma_buf_start_cpu_access(); void *ptr = dma_buf_vmap(); /*Access the buffer pointed by ptr*/ dma_buf_vunmap(ptr); dma_buf_end_cpu_access(); But on 64 bit platforms, there are no such restrictions (there is no highmem at all). So, frequently accessed buffer, may be mapped once, but every access should be surrounded by : dma_buf_start_cpu_access(); /*Access the buffer pointed by ptr*/ dma_buf_end_cpu_access() Am I correct? Thanks, Alexey
