Re: [PATCH 0/2] vb2: add (un)prepare_streaming vb2_queue ops

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Hans,

On Wed, Jun 22, 2022 at 11:31:43AM +0200, Hans Verkuil wrote:
> Add support for two new (un)prepare_streaming queue ops that are called
> when the user calls VIDIOC_STREAMON and STREAMOFF (or closes the fh).
> 
> This gives drivers a callback to validate the video pipeline and claim
> or release streaming resources at the time that userspace indicates
> that it wants to start streaming (VIDIOC_STREAMON) rather than when
> the actual DMA engine kicks in (the start_streaming callback). This
> is relevant for drivers that needs a minimum of X buffers before the
> DMA can start. The actual pipeline validation needs to happen sooner
> to avoid unnecessary errors at VIDIOC_QBUF time.
> 
> As a bonus this allows us to move the horrible call to
> v4l_vb2q_enable_media_source() in vb2_core_streamon() to the au0828
> driver (currently the only driver that uses this feature).

Can we drop the horrible .enable_source() from media_device too ? :-)

> That call never belonged in vb2, but it had the same purpose as the
> new prepare_streaming op: validate the pipeline.
> 
> This is a follow-up from my previous RFCv2:
> 
> https://patchwork.linuxtv.org/project/linux-media/patch/ba4bca14-488f-94ea-48d9-e7343103c5aa@xs4all.nl/
> 
> I would like to get consensus for this series.

I don't like it much. vb2 is already doing too much in my opinion,
growing it isn't the right way to fix it.

I'm still working on a new version of the V4L2 streams series that may
conflict with this, I'd propose discussing the two together.

> Hans Verkuil (2):
>   vb2: add (un)prepare_streaming queue ops
>   vb2/au0828: move the v4l_vb2q_enable_media_source to the au0828 driver
> 
>  .../media/common/videobuf2/videobuf2-core.c   | 26 ++++++++++++++-----
>  drivers/media/usb/au0828/au0828-vbi.c         |  2 ++
>  drivers/media/usb/au0828/au0828-video.c       |  1 +
>  include/media/videobuf2-core.h                | 14 ++++++++++
>  4 files changed, 37 insertions(+), 6 deletions(-)

-- 
Regards,

Laurent Pinchart