[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] swiotlb-xen question
On Tue, 1 Apr 2014, Oleksandr Dmytryshyn wrote: > Hi to all. I've investigated my issue deeper. > > Currently we use mmap in 2 cases: video-in (camera) and video-out (display). > > In case video-out all is working because mmap callback in the video-out device > leads to the remap_pfn_range() function (this function doesn't use > unimplemented > .mmap callback in the swiotlb-xen.c file). > > In case video-out mmap callback in the video-in device leads to the .mmap > callback from the dma ops (unimplemented callback in the swiotlb-xen.c file) > > I've investigated kernel code. We have patch from the Stefano Stabellini > (068a6e62 - arm/xen: get_dma_ops: return xen_dma_ops if we are running as > xen_initial_domain) > > Before this patch the function *get_dma_ops() always returned > __generic_dma_ops() > which returned &arm_dma_ops (if archdata.dma_ops is absent). In this case > for arm architecture .mmap callback is arm_dma_mmap() function. > > After this patch for domU all is the same as before this patch. But in case > dom0 kernel uses xen_dma_ops with unimplemented .mmap callback. If some > function tries to use .mmap callback in dom0 then kernel calls generic > function dma_common_mmap() which doesn't work properly. > > May be some mechanism for swiotlb-xen should be implemented for unimplemented > callbacks: if callback is not implemented then right architectural callback > should be used (.mmap - arm_dma_mmap() for ARM)? I understand now. Thanks for investingating! I think that we'll have to introduce our own version of .mmap, because dma_to_pfn doesn't work correctly on Xen on ARM. The implementation would be something like (untested): int xen_swiotlb_dma_mmap(struct device *dev, struct vm_area_struct *vma, void *cpu_addr, dma_addr_t dma_addr, size_t size, struct dma_attrs *attrs) { int ret = -ENXIO; #ifdef CONFIG_MMU unsigned long nr_vma_pages = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT; unsigned long nr_pages = PAGE_ALIGN(size) >> PAGE_SHIFT; unsigned long pfn = PFN_DOWN(xen_bus_to_phys(dev, dma_addr)); unsigned long off = vma->vm_pgoff; vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot); if (dma_mmap_from_coherent(dev, vma, cpu_addr, size, &ret)) return ret; if (off < nr_pages && nr_vma_pages <= (nr_pages - off)) { ret = remap_pfn_range(vma, vma->vm_start, pfn + off, vma->vm_end - vma->vm_start, vma->vm_page_prot); } #endif /* CONFIG_MMU */ return ret; } then we can add the function to xen_swiotlb_dma_ops. Would you be up for coming up with a proper patch? _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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