On Tue, Apr 11, 2017 at 04:39:09PM -0700, Stefano Stabellini wrote: > On Tue, 11 Apr 2017, Catalin Marinas wrote: > > On Tue, Apr 11, 2017 at 01:43:28PM +0100, Julien Grall wrote: > > > On 11/04/17 02:14, Bart Van Assche wrote: > > > > On 04/10/17 17:31, Stefano Stabellini wrote: > > > >> I think the reason is that, as you can see, if (dev && dev->dma_ops), > > > >> dev->dma_ops is returned, while before this changes, xen_dma_ops was > > > >> returned on Xen on ARM. > > > >> > > > >> Unfortunately DMA cannot work properly without using the appropriate > > > >> xen_dma_ops. See drivers/xen/swiotlb-xen.c and arch/arm/xen/mm.c for > > > >> more details. (The problem is easy to spot, but I wasn't CC'ed on the > > > >> patch.) > > > >> > > > >> I don't know how to solve this problem without introducing some sort of > > > >> if (xen()) in include/linux/dma-mapping.h. > > > > > > > > Sorry but I don't have access to an ARM development system. Does your > > > > comment apply to dev == NULL only, dev != NULL only or perhaps to both? > > > > If your comment applies to dev != NULL only, can you check whether > > > > adding something like set_dma_ops(dev, get_arch_dma_ops(NULL)) to the > > > > appropriate ARM arch_setup_dma_ops() function is sufficient? > > > > > > If I understand correctly, set_dma_ops will replace dev->dma_ops with > > > Xen DMA ops. [...] > > Yet another way would be for dom0 to always set dev->dma_ops to > > xen_dma_ops and preserve the real dma_ops somewhere under dev->archdata. > > You could intercept the arch_setup_dma_ops() function for this or use > > bus_register_notifier() (though I think the former is easier). The Xen > > code making use of the real dma_ops would have to dig them out from > > dev->archdata. > > This is a good suggestion, Catalin. Thank you. See below. Is that what > you have in mind? Julien could you test it, please? If it is the right > approach, I'll submit the patch properly and rename __generic_dma_ops to > xen_generic_dma_ops or something. It looks fine to me (subject to testing successfully). -- Catalin
