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

[<Eugen.Hristev@microchip.com>]

On 11/4/22 11:46, Hans Verkuil wrote:
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> 
> 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 :-)

Hello,

The ISC driver looks more clean with these ops.
I don't know how much it matters though.
It's not a big improvement, rather small, but it looks cleaner.

Thanks,
Eugen

> 
> 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(-)
>>
>