(CC: Jiri Slaby, the author of the problematic change; truncate subject) On Sat, 09 Apr 2011, at 09:16:24, Russell King - ARM Linux wrote: > On Sat, Apr 09, 2011 at 03:33:39AM +0200, Janusz Krzysztofik wrote: > > Since there were no actual problems reported before, I suppose the > > old code, which was passing to remap_pfn_range() a physical page > > number calculated from dma_alloc_coherent() privided dma_handle, > > worked correctly on all platforms actually using > > videobud-dma-config. Now, on my ARM machine, a completely > > different, then completely wrong physical address, calculated as > > virt_to_phys(dma_alloc_coherent()), is used instead of the > > dma_handle, which causes the machine to hang. > > virt_to_phys(dma_alloc_coherent()) is and always has been invalid, > and will break on several architectures apart from ARM. Hi Russell, Thanks for confirmation. For now, I have two working, but not very elegant, solutions: 1. For architectures which provide dma_mmap_coherent() (only ARM for now), use it instead of remap_pfn_range(). However, this requires setting vma->vm_pgoff to 0 before calling dma_mmap_coherent(). I don't really understand what this vma->vm_pgoff business is all about, I've only verified that: a) a non-zero value, comming with any but the first buffer, for a reason not quite clear to me, breaks comparison of the requested vma size, calculated as: (vma->vm_end - vma->vm_start) >> PAGE_SHIFT with the just allocated arm_vmregion avaliable space, calculated as: ((c->vm-end - c->vm_start) >> PAGE_SHIFT) - vma->vm_pgoff b) vma->vm_pgoff is overwriten, for a reason not quite clear to me, by remap_pfn_range() called from dma_mmap_coherent(), so first resetting its value to 0 should not affect anything else but dma_mmap_coherent(). If someone can explain me how this vm_pgoff handling inconsistency should be fixed without dirty hacks, I can try to implement it. 2. Use depreciated bus_to_virt(dma_handle) instead of mem->vaddr, like this: remap_pfn_range(..., PFN_DOWN(virt_to_phys(bus_to_virt(dma_handle))), ...) If 1. is acceppted, then 2. may still be considered for architectures which neither support virt_to_phys(dma_alloc_coherent()) nor provide their own dma_mmap_coherent() implementation. Thanks, Janusz -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
