Re: [RFCv1 PATCH 4/6] videobuf2-core: fill in length field for multiplanar buffers.

[Sylwester Nawrocki <s.nawrocki@samsung.com>]

On 09/21/2012 06:23 PM, Hans Verkuil wrote:
> On Fri September 21 2012 18:13:20 Sylwester Nawrocki wrote:
>> Hi Hans,
>>
>> On 09/19/2012 04:37 PM, Hans Verkuil wrote:
>>> From: Hans Verkuil <hans.verkuil@cisco.com>
>>>
>>> length should be set to num_planes in __fill_v4l2_buffer(). That way the
>>> caller knows how many planes there are in the buffer.
>>>
>>> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
>>
>> I think this would break VIDIOC_CREATE_BUFS. We need per buffer num_planes.
>> Consider a use case where device is streaming with 2-planar pixel format
>> and we invoke VIDIOC_CREATE_BUFS with single-planar format. On a single 
>> queue there will be buffers with different number of planes. The number of 
>> planes information must be attached to a buffer, otherwise VIDIOC_QUERYBUF 
>> won't work.
> 
> That's a very good point and one I need to meditate on.
> 
> However, your comment applies to patch 1/6, not to this one.
> This patch is about whether or not the length field of v4l2_buffer should
> be filled in with the actual number of planes used by that buffer or not.

Yes, right. Sorry, I was editing response to multiple patches from this
series and have mixed things a bit. I agree that it is logical and expected
to update struct v4l2_buffer for user space.

I have spent some time on this series, and even prepared a patch for s5p-mfc,
as it relies on num_planes being in struct vb2_buffer. But then a realized
there could be buffers with distinct number of planes an a single queue.

Regards,
Sylwester