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V4L: videobuf, don't use dma addr as physical

media Benjamin Herrenschmidt 1 participant 1 message Mar 25, 2011 1 message not in the archive

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Benjamin Herrenschmidt

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Quoted 15 lines · Linux Kernel Mailing List
Gitweb:     http://git.kernel.org/linus/35d9f510b67b10338161aba6229d4f55b4000f5b
Commit:     35d9f510b67b10338161aba6229d4f55b4000f5b
Parent:     4093a5c4a3f59cba1a085bbf87b6ffdddc5a443d
Author:     Jiri Slaby <[email protected]>
AuthorDate: Mon Feb 28 06:37:02 2011 -0300
Committer:  Mauro Carvalho Chehab <[email protected]>
CommitDate: Tue Mar 22 06:51:54 2011 -0300

[media] V4L: videobuf, don't use dma addr as physical

mem->dma_handle is a dma address obtained by dma_alloc_coherent which needn't be a physical address in presence of IOMMU, as
a hardware IOMMU can (and most likely) will return a bus address where physical != bus address.

Quoted 5 lines

So ensure we are remapping (remap_pfn_range) the right page in __videobuf_mmap_mapper by using virt_to_phys(mem->vaddr) and not mem->dma_handle.

While at it, use PFN_DOWN instead of explicit shift.

Sadly that doesn't work on all archs either... some will return addresses in the "vmalloc" space from dma_alloc_coherent() (due to the need to create non-cachable mappings there) and you can't pass those through virt_to_phys() either.

I'm sad that thing got merged at all. This whole videobuf2 looks like an unreviewed pile of crap to me. It re-invents dma pool management, re-invents even kref's, etc...

As for mmap'ing DMA, there's an attempt at fixing that done by the Alsa folks in the form of dma_mmap_coherent(). (See sound/core/pcm_native.c).

Only ARM implements it now. We need to move the

#define ARCH_HAS_DMA_MMAP_COHERENT

Out of the sound code into an ARM header tho, that way you can use it too, and I shall implement a variant for non-coherent embedded PPCs while at it (I'll take care of that last part).

Ben.

Quoted 25 lines
[[email protected]: Fix compilation breakage due to the lack of a comma]
Signed-off-by Jiri Slaby <[email protected]>
Reviewed-by Konrad Rzeszutek Wilk <[email protected]>
Signed-off-by Mauro Carvalho Chehab <[email protected]>
---
 drivers/media/video/videobuf-dma-contig.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
drivers/media/video/videobuf-dma-contig.c +1 -2
index c969111..c4742fc 100644
@@ -300,7 +300,7 @@ static int __videobuf_mmap_mapper(struct videobuf_queue *q,
 
 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 	retval = remap_pfn_range(vma, vma->vm_start,
-				 mem->dma_handle >> PAGE_SHIFT,
+				 PFN_DOWN(virt_to_phys(mem->vaddr)),
 				 size, vma->vm_page_prot);
 	if (retval) {
 		dev_err(q->dev, "mmap: remap failed with error %d. ", retval);
--

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