After switching from mem->dma_handle to virt_to_phys(mem->vaddr) used for obtaining page frame number passed to remap_pfn_range() (commit 35d9f510b67b10338161aba6229d4f55b4000f5b), videobuf-dma-contig stopped working on my ARM based board. The ARM architecture maintainer, Russell King, confirmed that using something like virt_to_phys(dma_alloc_coherent()) is not supported on ARM, and can be broken on other architectures as well. The author of the change, Jiri Slaby, also confirmed that his code may not work on all architectures.
The patch takes two different countermeasures against this regression: 1. On architectures which provide dma_mmap_coherent() function (ARM for now), use it instead of just remap_pfn_range(). The code is stollen from sound/core/pcm_native.c:snd_pcm_default_mmap(). Set vma->vm_pgoff to 0 before calling dma_mmap_coherent(), or it fails. 2. On other architectures, use virt_to_phys(bus_to_virt(mem->dma_handle)) instead of problematic virt_to_phys(mem->vaddr). This should work even if those translations would occure inaccurate for DMA addresses, since possible errors introduced by both calculations, performed in opposite directions, should compensate. Both solutions tested on ARM OMAP1 based Amstrad Delta board. Signed-off-by: Janusz Krzysztofik <[email protected]> --- drivers/media/video/videobuf-dma-contig.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) --- linux-2.6.39-rc2/drivers/media/video/videobuf-dma-contig.c.orig 2011-04-09 00:38:45.000000000 +0200 +++ linux-2.6.39-rc2/drivers/media/video/videobuf-dma-contig.c 2011-04-10 15:00:23.000000000 +0200 @@ -295,13 +295,26 @@ static int __videobuf_mmap_mapper(struct /* Try to remap memory */ +#ifndef ARCH_HAS_DMA_MMAP_COHERENT +/* This should be defined / handled globally! */ +#ifdef CONFIG_ARM +#define ARCH_HAS_DMA_MMAP_COHERENT +#endif +#endif + +#ifdef ARCH_HAS_DMA_MMAP_COHERENT + vma->vm_pgoff = 0; + retval = dma_mmap_coherent(q->dev, vma, mem->vaddr, mem->dma_handle, + mem->size); +#else size = vma->vm_end - vma->vm_start; size = (size < mem->size) ? size : mem->size; vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot); retval = remap_pfn_range(vma, vma->vm_start, - PFN_DOWN(virt_to_phys(mem->vaddr)), - size, vma->vm_page_prot); + PFN_DOWN(virt_to_phys(bus_to_virt(mem->dma_handle))), + size, vma->vm_page_prot); +#endif if (retval) { dev_err(q->dev, "mmap: remap failed with error %d. ", retval); dma_free_coherent(q->dev, mem->size, -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
