On Tue, Aug 04, 2015 at 03:47:13PM +0100, Robin Murphy wrote: > Hi Laurent, > > [ +RMK, as his patch is indirectly involved here ] > > On 04/08/15 14:16, Laurent Pinchart wrote: > >This is what I believe to be an API abuse. The dma_sync_single_for_device() > >API is meant to pass ownership of a buffer to the device. Unless I'm > >mistaken, > >once that's done the CPU isn't allowed to touch the buffer anymore until > >dma_sync_single_for_cpu() is called to get ownership of the buffer back.
That's what I thought up until recently, but it's not strictly true - see Documentation/DMA-API.txt which Robin quoted. > [3]:Yes, there may generally be exceptions to that, but not in the context > of this code. Unless the Renesas IPMMU does something I don't know about? If an IOMMU does write to its page tables, then the only way to handle those is using DMA-coherent memory, either via a coherent mapping or allocated via dma_alloc_coherent(). The streaming DMA API is wholely unsuitable for any mapping where both the CPU and DMA device both want to simultaneously alter the contained data. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
