linux-kernel - Re: [PATCH v2 0/3] media: vimc: Allow multiple capture devices to use the same sensor

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Message-ID: <3a9ac970-77b8-1bc5-536a-5b4f2bd60745@collabora.com>
Date:   Tue, 28 Jul 2020 14:07:29 +0200
From:   Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
To:     Kaaira Gupta <kgupta@...iitr.ac.in>,
        Helen Koike <helen.koike@...labora.com>
Cc:     kieran.bingham@...asonboard.com,
        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
Subject: Re: [PATCH v2 0/3] media: vimc: Allow multiple capture devices to use
 the same sensor

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.

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
>>>