[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v8 13/19] swiotlb-xen: use xen_dma_map/unmap_page, xen_dma_sync_single_for_cpu/device
On Thu, Oct 24, 2013 at 11:44:50AM +0100, Stefano Stabellini wrote: > On Wed, 23 Oct 2013, Konrad Rzeszutek Wilk wrote: > > On Wed, Oct 23, 2013 at 06:20:25PM +0100, Stefano Stabellini wrote: > > > On Wed, 23 Oct 2013, Konrad Rzeszutek Wilk wrote: > > > > On Thu, Oct 17, 2013 at 06:43:28PM +0100, Stefano Stabellini wrote: > > > > > Call xen_dma_map_page, xen_dma_unmap_page, > > > > > xen_dma_sync_single_for_cpu, > > > > > xen_dma_sync_single_for_device from swiotlb-xen to ensure cpu/device > > > > > coherency of the pages used for DMA, including the ones belonging to > > > > > the > > > > > swiotlb buffer. > > > > > > > > You lost me. > > > > > > > > Isn't it the driver's responsibility to do this? > > > > > > > > Looking at what 'xen_dma_map_page()' does for x86 it looks to add an > > > > extra > > > > call - page_to_phys - and we ignore it here. > > > > > > map_page on arm calls the right cache flushes needed to communicate with > > > the device. Same with unmap_page. > > > > If this is flushing the cache then I think it makes more sense to do > > that without this fancy 'dma_map_page'. > > > > Just call it 'xen_flush_dma_page' and make it a nop on all platforms > > except ARM. > > I am OK with making it a nop on x86, it makes sense. > However I would like to keep it called xen_dma_map_page: after all it > corresponds exactly to the native map_page dma_op. It is part of the same > "contract". OK. > > > > > On x86 they are basically nop. > > > > It calls page_to_phys in your patch. That is hardly nop. > > I see. It is certainly worth optimizing it out on x86. > Of course if one day the x86 map_page dma_op starts doing something > useful, we can go back to call it from xen_dma_map_page. Sure. _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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