On 02/22/22 at 04:59pm, Christoph Hellwig wrote: > On Tue, Feb 22, 2022 at 09:41:43PM +0800, Baoquan He wrote: > > For newly added streaming mapping APIs, the internal core function > > __dma_alloc_pages() should check dev->dma_mask, but not > > ev->coherent_dma_mask which is for coherent mapping. > > No, this is wrong. dev->coherent_dma_mask is and should be used here. 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 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. > > > > > > > Meanwhile, just filter out gfp flags if they are any of > > __GFP_DMA, __GFP_DMA32 and __GFP_HIGHMEM, but not fail it. This change > > makes it consistent with coherent mapping allocs. > > This is wrong as well. We want to eventually fail dma_alloc_coherent > for these, too. It just needs more work. >
