linux-kernel - Re: [PATCH] [media] videobuf-dma-contig: replace vm_iomap_memory() with remap_pfn

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Date:	Wed, 10 Sep 2014 09:21:21 +0200
From:	Hans Verkuil <hverkuil@...all.nl>
To:	"chen.fang@...escale.com" <chen.fang@...escale.com>,
	"m.chehab@...sung.com" <m.chehab@...sung.com>,
	"viro@...IV.linux.org.uk" <viro@...IV.linux.org.uk>
CC:	Shawn Guo <Shawn.Guo@...escale.com>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH] [media] videobuf-dma-contig: replace vm_iomap_memory()
 with remap_pfn_range().

On 09/10/14 09:14, chen.fang@...escale.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@...all.nl] 
> Sent: Wednesday, September 10, 2014 3:01 PM
> To: Fang Chen-B47543; m.chehab@...sung.com; viro@...IV.linux.org.uk
> Cc: Guo Shawn-R65073; linux-media@...r.kernel.org; linux-kernel@...r.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@...escale.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);
>>
> 

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