Re: [media] uvcvideo: support for contiguous DMA buffers

[Vincent ABRIOU <vincent.abriou@st.com>]

Hi Laurent,

On 01/09/2017 05:59 PM, Laurent Pinchart wrote:
> Hi Vincent,
>
> (CC'ing Nicolas)
>
> On Monday 09 Jan 2017 15:49:00 Vincent ABRIOU wrote:
>> On 01/09/2017 04:37 PM, Laurent Pinchart wrote:
>>> Hi Vincent,
>>>
>>> Thank you for the patch.
>>>
>>> On Monday 03 Oct 2016 13:27:16 Vincent Abriou wrote:
>>>> Allow uvcvideo compatible devices to allocate their output buffers using
>>>> contiguous DMA buffers.
>>>
>>> Why do you need this ? If it's for buffer sharing with a device that
>>> requires dma-contig, can't you allocate the buffers on the other device
>>> and import them on the UVC side ?
>>
>> Hi Laurent,
>>
>> I need this using Gstreamer simple pipeline to connect an usb webcam
>> (v4l2src) with a display (waylandsink) activating the zero copy path.
>>
>> The waylandsink plugin does not have any contiguous memory pool to
>> allocate contiguous buffer. So it is up to the upstream element, here
>> v4l2src, to provide such contiguous buffers.
>
> Isn't that a gstreamer issue ?
>

It is not a gstreamer issue. It is the way it has been decided to work.
Waylandsink accept DMABUF contiguous buffer but it does not have its own 
buffer pool.

Vincent

>>>> Add the "allocators" module parameter option to let uvcvideo use the
>>>> dma-contig instead of vmalloc.
>>>>
>>>> Signed-off-by: Vincent Abriou <vincent.abriou@st.com>
>>>> ---
>>>>
>>>>  Documentation/media/v4l-drivers/uvcvideo.rst | 12 ++++++++++++
>>>>  drivers/media/usb/uvc/Kconfig                |  2 ++
>>>>  drivers/media/usb/uvc/uvc_driver.c           |  3 ++-
>>>>  drivers/media/usb/uvc/uvc_queue.c            | 23 ++++++++++++++++++---
>>>>  drivers/media/usb/uvc/uvcvideo.h             |  4 ++--
>>>>  5 files changed, 38 insertions(+), 6 deletions(-)
>