On Wed, Apr 11, 2018 at 09:28:54AM +0200, Takashi Iwai wrote: > > But we should try a GFP_DMA32 allocation first, so this is a bit > > surprising. > > Hm, do we really try that? > Through a quick glance, dma_alloc_coherent_gfp_flags() gives GFP_DMA32 > only when coherent mask <= DMA_BIT_MASK(32); in the case of iwlwifi, > it's 36bit, so GFP_DMA isn't set.
Oh, yes - it is using an odd dma mask, and amdgpu seems to use an just as odd 40-bit dma mask. > We had a fallback allocation with GFP_DMA32 in the past, but this > seems gone long time ago along with cleanups (commit c647c3bb2d16). > > But I haven't followed about this topic for long time, so I might have > missed obviously... I think a fallback would be much better here rather than relying on the limited swiotlb buffer bool. dma_direct_alloc (which in 4.17 is also used for x86) already has a GFP_DMA fallback, so extending this for GFP_DMA32 as well would seem reasonable. Any volunteers? _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
