On Mon, Jul 13, 2020 at 12:55:43PM +0100, Robin Murphy wrote: > On 2020-07-13 10:12, Claire Chang wrote: >> The bounced DMA ops provide an implementation of DMA ops that bounce >> streaming DMA in and out of a specially allocated region. Only the >> operations relevant to streaming DMA are supported. > > I think there are too many implicit assumptions here - apparently that > coherent allocations will always be intercepted by > dma_*_from_dev_coherent(), and that calling into dma-direct won't actually > bounce things a second time beyond where you thought they were going, > manage coherency for a different address, and make it all go subtly wrong. > Consider "swiotlb=force", for instance... > > Again, plumbing this straight into dma-direct so that SWIOTLB can simply > target a different buffer and always bounce regardless of masks would seem > a far better option. I haven't really had time to read through the details, but I agree that any bouncing scheme should reuse the swiotlb code and not invent a parallel infrastructure.
