On Mon, Mar 16, 2020 at 12:12:08PM +0000, Robin Murphy wrote: > On 2020-03-14 12:00 am, Nicolin Chen wrote: >> More and more drivers set dma_masks above DMA_BIT_MAKS(32) while >> only a handful of drivers call dma_set_seg_boundary(). This means >> that most drivers have a 4GB segmention boundary because DMA API >> returns DMA_BIT_MAKS(32) as a default value, though they might be >> able to handle things above 32-bit. > > Don't assume the boundary mask and the DMA mask are related. There do exist > devices which can DMA to a 64-bit address space in general, but due to > descriptor formats/hardware design/whatever still require any single > transfer not to cross some smaller boundary. XHCI is 64-bit yet requires > most things not to cross a 64KB boundary. EHCI's 64-bit mode is an example > of the 4GB boundary (not the best example, admittedly, but it undeniably > exists).
Yes, which is what the boundary is for. But why would we default to something restrictive by default even if the driver didn't ask for it? _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
