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 12:00:58PM +0200, Hans Verkuil wrote:
> On 22/06/2022 11:44, Laurent Pinchart wrote:
> > 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 ? :-)
> 
> The second patch helps a bit with that, at least it's out of vb2.
> 
> > 
> >> 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.
> 
> We disagree on that :-)

I like polite and constructive disagreements, they help moving forward
:-)

> > 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.
> 
> What is the ETA for that? I don't mind waiting a few months, but if it
> takes a lot longer, then I'd rather merge this first so Eugen can use it
> in his atmel MC support. It's a kernel API, so it can always be changed
> or removed later.

I have a few other things to complete first, an dI plan to resume the
work in the first half of July, to post a v12 before the end of the
month.

> >> 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