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

Hans Verkuil
2014-09-10T07:22:34Z

On 09/10/14 09:14, chen.fang@freescale.com wrote:
> It is not a theoretically issue, it is a real case that the mapping failed issue happens in 3.14.y kernel but not happens in previous 3.10.y kernel.
> So I need your confirmation on it.

With which driver does this happen? On which architecture?

Regards,

Hans

>
> Thanks.
>
> Best regards,
> Fancy Fang
>
> -----Original Message-----
> From: Hans Verkuil [mailto:hverkuil@xs4all.nl]
> Sent: Wednesday, September 10, 2014 3:01 PM
> To: Fang Chen-B47543; m.chehab@samsung.com; viro@ZenIV.linux.org.uk
> Cc: Guo Shawn-R65073; linux-media@vger.kernel.org; linux-kernel@vger.kernel.org; Marek Szyprowski
> Subject: Re: [PATCH] [media] videobuf-dma-contig: replace vm_iomap_memory() with remap_pfn_range().
>
> 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);
>>
>