Thanks for your idea, Marek and Hans. This change makes sense. And I've already verified it. I'll resubmit my change soon. Best regards, Fancy Fang -----Original Message----- From: Hans Verkuil [mailto:hverkuil@xxxxxxxxx] Sent: Wednesday, September 24, 2014 8:43 PM To: Marek Szyprowski; Fang Chen-B47543; m.chehab@xxxxxxxxxxx; viro@xxxxxxxxxxxxxxxxxx Cc: Guo Shawn-R65073; linux-media@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx Subject: Re: [PATCH] [media] videobuf-dma-contig: replace vm_iomap_memory() with remap_pfn_range(). On 09/24/2014 02:40 PM, Marek Szyprowski wrote: > Hello, > > On 2014-09-10 09:00, Hans Verkuil wrote: >> 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. > > I'm sorry for a delay, I was really busy with other things. > >>> Signed-off-by: Fancy Fang <chen.fang@xxxxxxxxxxxxx> >>> --- >>> 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); > > I think we don't need to revert the code to use remap_pfn_range() > again (like it was in pre v3.10 times). The simplest way will be to > correctly fix > vma->vm_pgoff and set it to zero before calling vm_iomap_memory(). It > vma->is > done the same way in vb2_dma_contig.c:vb2_dc_mmap(). > > To sum up - please change your patch: keep vm_iomap_memory() call and > add "vma->vm_pgoff = 0;" line before it with suitable comment. Much better, I agree completely. Regards, Hans ��.n��������+%������w��{.n�����{��g����^n�r������&��z�ޗ�zf���h���~����������_��+v���)ߣ�
