On 11/12/2014 11:18 PM, Gioh Kim wrote: > Hi, > > I'm wondering why dma_alloc_coherent needs GFP_HIGHUSER | __GFP_ZERO flags in ion_cma_allocate(). > > I think dma_alloc_coherent can go to __dma_alloc if the system has CMA area. > If __GFP_WAIT flag is set, it allocates memory from atomic pool. > So I think calling dma_alloc_coherent with __GFP_WAIT is enough. > > And can I get zero-filled-memory from CMA if I set __GFP_ZERO? > > If we are actually using CMA, the GFP flags don't make much of a difference. If we didn't have CMA, using GFP_HIGHUSER would still be appropriate. The memory is going to userspace so the user part is necessary and there should be no need for a lowmem mapping so highmem can be used. __GFP_ZERO might be redundant since the dma layer zeros memory anyway but it's probably safe. I think the flags should be fine as is. Thanks, Laura -- Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
