Date:   Wed, 29 Jul 2020 14:05:29 +0100
From:   Kieran Bingham <kieran.bingham@...asonboard.com>
To:     Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Kaaira Gupta <kgupta@...iitr.ac.in>,
        Helen Koike <helen.koike@...labora.com>
Cc:     Niklas Söderlund <niklas.soderlund@...natech.se>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hans Verkuil <hverkuil@...all.nl>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Ezequiel Garcia <ezequiel@...labora.com>
Subject: Re: [PATCH v2 0/3] media: vimc: Allow multiple capture devices to use
 the same sensor

Hi Dafna,

On 28/07/2020 15:00, Dafna Hirschfeld wrote:
> 
> 
> On 28.07.20 14:07, Dafna Hirschfeld wrote:
>> Hi
>>
>> On 28.07.20 13:39, Kaaira Gupta wrote:
>>> On Mon, Jul 27, 2020 at 02:54:30PM -0300, Helen Koike wrote:
>>>> Hi,
>>>>
>>>> On 7/27/20 11:31 AM, Kieran Bingham wrote:
>>>>> Hi all,
>>>>>
>>>>> +Dafna for the thread discussion, as she's missed from the to/cc list.
>>>>>
>>>>>
>>>>> On 24/07/2020 13:21, Kaaira Gupta wrote:
>>>>>> On Fri, Jul 24, 2020 at 02:15:21PM +0200, Niklas Söderlund wrote:
>>>>>> Hi,
>>>>>>
>>>>>>> Hi Kaaira,
>>>>>>>
>>>>>>> Thanks for your work.
>>>>>>
>>>>>> Thanks for yours :D
>>>>>>
>>>>>>>
>>>>>>> On 2020-07-24 17:32:10 +0530, Kaaira Gupta wrote:
>>>>>>>> This is version 2 of the patch series posted by Niklas for allowing
>>>>>>>> multiple streams in VIMC.
>>>>>>>> The original series can be found here:
>>>>>>>> https://patchwork.kernel.org/cover/10948831/
>>>>>>>>
>>>>>>>> This series adds support for two (or more) capture devices to be
>>>>>>>> connected to the same sensors and run simultaneously. Each
>>>>>>>> capture device
>>>>>>>> can be started and stopped independent of each other.
>>>>>>>>
>>>>>>>> Patch 1/3 and 2/3 deals with solving the issues that arises once
>>>>>>>> two
>>>>>>>> capture devices can be part of the same pipeline. While 3/3
>>>>>>>> allows for
>>>>>>>> two capture devices to be part of the same pipeline and thus
>>>>>>>> allows for
>>>>>>>> simultaneously use.
>>
>> I wonder if these two patches are enough, since each vimc entity also
>> have
>> a 'process_frame' callback, but only one allocated frame. That means
>> that the 'process_frame' can be called concurrently by two different
>> streams
>> on the same frame and cause corruption.
>>
> 
> I think we should somehow change the vimc-stream.c code so that we have
> only
> one stream process per pipe. So if one capture is already streaming,
> then the new
> capture that wants to stream uses the same thread so we don't have two
> threads
> both calling 'process_frame'.


Yes, I think it looks and sounds like there are two threads running when
there are two streams.

so in effect, although they 'share a pipe', aren't they in effect just
sending two separate buffers through their stream-path?

If that's the case, then I don't think there's any frame corruption,
because they would both have grabbed their own frame separately.


I don't think that's a good example of the hardware though, as that
doesn't reflect what 'should' happen where the TPG runs once to generate
a frame at the sensor, which is then read by both the debayer entity and
the RAW capture device when there are two streams...


So I suspect trying to move to a single thread is desirable, but that
might be a fair bit of work also.

--
Kieran



> The second capture that wants to stream should iterate the topology
> downwards until
> reaching an entity that already belong to the stream path of the other
> streaming capture
> and tell the streamer it wants to read the frames this entity
> produces.
> 
> Thanks,
> Dafna
> 
>> Thanks,
>> Dafna
>>
>>>>>>>
>>>>>>> I'm just curious if you are aware of this series? It would
>>>>>>> replace the
>>>>>>> need for 1/3 and 2/3 of this series right?
>>>>>>
>>>>>> v3 of this series replaces the need for 1/3, but not the current
>>>>>> version
>>>>>> (ie v4). v4 of patch 2/5 removes the stream_counter that is needed to
>>>>>> keep count of the calls to s_stream. Hence 1/3 becomes relevant
>>>>>> again.
>>>>>
>>>>> So the question really is, how do we best make use of the two current
>>>>> series, to achieve our goal of supporting multiple streams.
>>>>>
>>>>> Having not parsed Dafna's series yet, do we need to combine
>>>>> elements of
>>>>> both ? Or should we work towards starting with this series and get
>>>>> dafna's patches built on top ?
>>>>>
>>>>> Or should patch 1/3 and 3/3 of this series be on top of Dafna's v4 ?
>>>>>
>>>>> (It might be noteworthy to say that Kaaira has reported successful
>>>>> multiple stream operation from /this/ series and her development
>>>>> branch
>>>>> on libcamera).
>>>>
>>>> Dafna's patch seems still under discussion, but I don't want to
>>>> block progress in Vimc either.
>>>>
>>>> So I was wondering if we can move forward with Vimc support for
>>>> multistreaming,
>>>> without considering Dafna's patchset, and we can do the clean up
>>>> later once we solve that.
>>>>
>>>> What do you think?
>>>
>>> I agree with supporting multiple streams with VIMC with this patchset,
>>> and then we can refactor the counters for s_stream in VIMC later (over
>>> this series) if dafna includes them in subsequent version of her
>>> patchset.
>>>
>>
>> I also think that adding support in the code will take much longer and
>> should not
>> stop us from supporting vimc independently.
>>
>> Thanks,
>> Dafna
>>
>>>>
>>>> Regards,
>>>> Helen
>>>>
>>>>>
>>>>>
>>>>>>> 1. 
>>>>>>> https://lore.kernel.org/linux-media/20200522075522.6190-1-dafna.hirschfeld@collabora.com/
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> Changes since v1:
>>>>>>>>     - All three patches rebased on latest media-tree.
>>>>>>>>     Patch 3:
>>>>>>>>     - Search for an entity with a non-NULL pipe instead of
>>>>>>>> searching
>>>>>>>>       for sensor. This terminates the search at output itself.
>>>>>>>>
>>>>>>>> Kaaira Gupta (3):
>>>>>>>>    media: vimc: Add usage count to subdevices
>>>>>>>>    media: vimc: Serialize vimc_streamer_s_stream()
>>>>>>>>    media: vimc: Join pipeline if one already exists
>>>>>>>>
>>>>>>>>   .../media/test-drivers/vimc/vimc-capture.c    | 35
>>>>>>>> ++++++++++++++++++-
>>>>>>>>   .../media/test-drivers/vimc/vimc-debayer.c    |  8 +++++
>>>>>>>>   drivers/media/test-drivers/vimc/vimc-scaler.c |  8 +++++
>>>>>>>>   drivers/media/test-drivers/vimc/vimc-sensor.c |  9 ++++-
>>>>>>>>   .../media/test-drivers/vimc/vimc-streamer.c   | 23 +++++++-----
>>>>>>>>   5 files changed, 73 insertions(+), 10 deletions(-)
>>>>>>>>
>>>>>>>> -- 
>>>>>>>> 2.17.1
>>>>>>>>
>>>>>>>
>>>>>>> -- 
>>>>>>> Regards,
>>>>>>> Niklas Söderlund
>>>>>

-- 
Regards
--
Kieran

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