[media] videobuf-dma-contig: set vm_pgoff to be zero to pass the sanity check in vm_iomap_memory()

When user requests V4L2_MEMORY_MMAP type buffers, the videobuf-core
will assign the corresponding offset to the 'boff' field of the
videobuf_buffer for each requested buffer sequentially. Later, user
may call mmap() to map one or all of the buffers with the 'offset'
parameter which is equal to its 'boff' value. Obviously, the 'offset'
value is only used to find the matched buffer instead of to be the
real offset from the buffer's physical start address as used by
vm_iomap_memory(). So, in some case that if the offset is not zero,
vm_iomap_memory() will fail.
Signed-off-by: Fancy Fang <chen.fang@freescale.com>
Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/v4l2-core/videobuf-dma-contig.c

@@ -305,6 +305,15 @@ static int __videobuf_mmap_mapper(struct videobuf_queue *q,
 	/* Try to remap memory */
 	size = vma->vm_end - vma->vm_start;
 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+
+	/* the "vm_pgoff" is just used in v4l2 to find the
+	 * corresponding buffer data structure which is allocated
+	 * earlier and it does not mean the offset from the physical
+	 * buffer start address as usual. So set it to 0 to pass
+	 * the sanity check in vm_iomap_memory().
+	 */
+	vma->vm_pgoff = 0;
+
 	retval = vm_iomap_memory(vma, mem->dma_handle, size);
 	if (retval) {
 		dev_err(q->dev, "mmap: remap failed with error %d. ",