On Wed, Feb 23, 2022 at 08:28:13AM +0800, Baoquan He wrote: > Could you tell more why this is wrong? According to > Documentation/core-api/dma-api.rst and DMA code, __dma_alloc_pages() is > the core function of dma_alloc_pages()/dma_alloc_noncoherent() which are > obviously streaming mapping, Why are they "obviously" streaming mappings? > why do we need to check > dev->coherent_dma_mask here? Because dev->coherent_dma_mask is the subset > of dev->dma_mask, it's safer to use dev->coherent_dma_mask in these > places? This is confusing, I talked to Hyeonggon in private mail, he has > the same feeling. Think of th coherent_dma_mask as dma_alloc_mask. It is the mask for the DMA memory allocator. dma_mask is the mask for the dma_map_* routines.
