On 2019-02-21 2:59 a.m., Koenig, Christian wrote: > On x86 with HIGHMEM there is no dma32 zone. Why do we need one on >>> x86_64? Can we make x86_64 more like HIGHMEM instead? >>> >>> Regards, >>> Felix >>> >> IIRC with x86, the kernel zone is always smaller than any dma32 zone, >> so we'd always exhaust the kernel zone before dma32 anyway. >> >> Not sure why we have dma32 on x86 without highmem, though. sounds >> superflous but harmless. > Well DMA32 denotes memory which is accessible by devices who can only do > 32bit addressing. And IIRC we can actually do DMA32 to highmem since > something like 2.4.*. > > Because of this it is actually irrelevant if you have highmem or not, > what matters for DMA32 is if you have an IOMMU or not. Are you saying we should have a dma32_zone even on x86 with HIGHMEM? > > So even on x86_64 you actually do need the DMA32 zone if you don't have > an IOMMU which remaps all memory for devices which can't directly > address it. Why is DMA32 special in this way? For example AMD GFX8 GPUs support 40-bit DMA. But we don't have a special zone for that. How common is it to have devices that need DMA32 on an x86_64 system? Regards, Felix > > Regards, > Christian. > >> /Thomas >> >> _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
