On Wed, May 22, 2019 at 02:25:38PM +0100, Robin Murphy wrote: > Sure, but that should be irrelevant since the effective problem here is in > the sync_*_for_cpu direction, and it's the unmap which nobbles the buffer. > If the driver does this: > > dma_map_single(whole buffer); > <device writes to part of buffer> > dma_unmap_single(whole buffer); > <contents of rest of buffer now undefined> > > then it could instead do this and be happy: > > dma_map_single(whole buffer, SKIP_CPU_SYNC); > <device writes to part of buffer> > dma_sync_single_for_cpu(updated part of buffer); > dma_unmap_single(whole buffer, SKIP_CPU_SYNC); > <contents of rest of buffer still valid>
Assuming the driver knows how much was actually DMAed this would solve the issue. Horia, does this work for you?
