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

[Hans Verkuil <hverkuil-cisco@xs4all.nl>]

Hi Laurent,

On 22/06/2022 12:08, Laurent Pinchart wrote:
> 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.

Looking at the latest v15 series there are no conflicts with this patch.

Eugen posted a v11 of his "atmel-isc: driver redesign" series, and wants
to use this functionality.

I think with this change it is also possible to remove the enable_source
callback from the mc. I can try to post a v2 that does this, if that's
what it takes to convince you :-)

Regards,

	Hans

> 
>>>> 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(-)
>