On 02/22/22 at 04:59pm, Christoph Hellwig wrote:

On Tue, Feb 22, 2022 at 09:41:43PM +0800, Baoquan He wrote:

quoted

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.

quoted

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.