Re: [PATCH] [media] videobuf-dma-contig: replace vm_iomap_memory() with remap_pfn_range().

Hans Verkuil
2014-09-10T07:01:42Z

On 09/10/14 07:28, Fancy Fang wrote:
> 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.

Is this just a fix for something that can fail theoretically, or do you
actually have a case where this happens? I am very reluctant to make
any changes to videobuf. Drivers should all migrate to vb2.

I have CC-ed Marek as well since he knows a lot more about this stuff
than I do.

Regards,

Hans

>
> Signed-off-by: Fancy Fang <chen.fang@freescale.com>
> ---
> drivers/media/v4l2-core/videobuf-dma-contig.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/v4l2-core/videobuf-dma-contig.c b/drivers/media/v4l2-core/videobuf-dma-contig.c
> index bf80f0f..8bd9889 100644
> --- a/drivers/media/v4l2-core/videobuf-dma-contig.c
> +++ b/drivers/media/v4l2-core/videobuf-dma-contig.c
> @@ -305,7 +305,9 @@ 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);
> - retval = vm_iomap_memory(vma, mem->dma_handle, size);
> + retval = remap_pfn_range(vma, vma->vm_start,
> + mem->dma_handle >> PAGE_SHIFT,
> + size, vma->vm_page_prot);
> if (retval) {
> dev_err(q->dev, "mmap: remap failed with error %d. ",
> retval);
>