Message-ID: <7300d7ab-2be0-a6c6-b506-5af8b4a9b893@ideasonboard.com>
Date:   Wed, 2 Sep 2020 11:29:31 +0100
From:   Kieran Bingham <kieran.bingham@...asonboard.com>
To:     Kaaira Gupta <kgupta@...iitr.ac.in>,
        Helen Koike <helen.koike@...labora.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 7/9] media: vimc: Dynamically allocate stream struct

Hi Kaaira,

On 19/08/2020 19:04, Kaaira Gupta wrote:
> Multiple streams will share same stream struct if we want them to run on
> same thread. So remove it from vimc_cap struct so that it doesn't get
> destroyed when one of the capture does, and allocate it memory
> dynamically. Use kref with it as it will be used by multiple captures.
> 

Is the vimc_stream stuct the context of the streamer? or of each 'stream'?

If it's the streamer - then can't we store this (non-dynamically) as
part of the Sensor node, to avoid kzalloc/freeing it ?


> Signed-off-by: Kaaira Gupta <kgupta@...iitr.ac.in>
> ---
>  drivers/media/test-drivers/vimc/vimc-capture.c  | 15 +++++++++++----
>  drivers/media/test-drivers/vimc/vimc-streamer.c | 17 ++++++-----------
>  drivers/media/test-drivers/vimc/vimc-streamer.h |  2 ++
>  3 files changed, 19 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/media/test-drivers/vimc/vimc-capture.c b/drivers/media/test-drivers/vimc/vimc-capture.c
> index 93418cb5a139..73e5bdd17c57 100644
> --- a/drivers/media/test-drivers/vimc/vimc-capture.c
> +++ b/drivers/media/test-drivers/vimc/vimc-capture.c
> @@ -28,7 +28,6 @@ struct vimc_cap_device {
>  	spinlock_t qlock;
>  	struct mutex lock;
>  	u32 sequence;
> -	struct vimc_stream stream;
>  	struct media_pad pad;
>  };
>  
> @@ -241,19 +240,25 @@ static int vimc_cap_start_streaming(struct vb2_queue *vq, unsigned int count)
>  {
>  	struct vimc_cap_device *vcap = vb2_get_drv_priv(vq);
>  	struct media_entity *entity = &vcap->vdev.entity;
> +	struct media_pipeline *pipe = NULL;
> +	struct vimc_stream *stream;
>  	int ret;
>  
>  	atomic_inc(&vcap->ved.use_count);
>  	vcap->sequence = 0;
>  
> +	stream = kzalloc(sizeof(*stream), GFP_ATOMIC);
> +	kref_init(&stream->refcount);
> +	pipe = &stream->pipe;
> +
>  	/* Start the media pipeline */
> -	ret = media_pipeline_start(entity, &vcap->stream.pipe);
> +	ret = media_pipeline_start(entity, pipe);
>  	if (ret) {
>  		vimc_cap_return_all_buffers(vcap, VB2_BUF_STATE_QUEUED);
>  		return ret;
>  	}
>  
> -	ret = vimc_streamer_s_stream(&vcap->stream, &vcap->ved, 1);
> +	ret = vimc_streamer_s_stream(stream, &vcap->ved, 1);
>  	if (ret) {
>  		media_pipeline_stop(entity);
>  		vimc_cap_return_all_buffers(vcap, VB2_BUF_STATE_QUEUED);
> @@ -270,9 +275,11 @@ static int vimc_cap_start_streaming(struct vb2_queue *vq, unsigned int count)
>  static void vimc_cap_stop_streaming(struct vb2_queue *vq)
>  {
>  	struct vimc_cap_device *vcap = vb2_get_drv_priv(vq);
> +	struct media_pipeline *pipe = vcap->ved.ent->pipe;
> +	struct vimc_stream *stream = container_of(pipe, struct vimc_stream, pipe);

In fact, I see it's stored as part of the 'pipe' so there is one
vimc_stream per pipeline ...

So it could just be a structure on the pipe rather than obtaining a
pointer here.

I think it's probably 'ok' to have one streamer per pipe currently as
the raw input node is not functional, but I also thought that by having
the streamer as part of the sensor entity then there is one streamer
('one thread') per video source ... which would prevent this having to
be changed if someone later deals with the video node that allows
re-processing raw frames ?



>  	atomic_dec(&vcap->ved.use_count);
> -	vimc_streamer_s_stream(&vcap->stream, &vcap->ved, 0);
> +	vimc_streamer_s_stream(stream, &vcap->ved, 0);
>  
>  	/* Stop the media pipeline */
>  	media_pipeline_stop(&vcap->vdev.entity);
> diff --git a/drivers/media/test-drivers/vimc/vimc-streamer.c b/drivers/media/test-drivers/vimc/vimc-streamer.c
> index f5c9e2f3bbcb..fade37bee26d 100644
> --- a/drivers/media/test-drivers/vimc/vimc-streamer.c
> +++ b/drivers/media/test-drivers/vimc/vimc-streamer.c
> @@ -20,18 +20,13 @@
>   * Erases values of stream struct and terminates the thread
>   *
>   */
> -static void vimc_streamer_pipeline_terminate(struct vimc_stream *stream)
> +static void vimc_streamer_pipeline_terminate(struct kref *ref)
>  {
> -	struct vimc_ent_device *ved;
> -
> -	while (stream->pipe_size) {
> -		stream->pipe_size--;
> -		ved = stream->ved_pipeline[stream->pipe_size];
> -		stream->ved_pipeline[stream->pipe_size] = NULL;
> -	}
> +	struct vimc_stream *stream = container_of(ref, struct vimc_stream, refcount);
>  
>  	kthread_stop(stream->kthread);
>  	stream->kthread = NULL;
> +	kfree(stream);
>  }
>  
>  /**
> @@ -202,7 +197,7 @@ static int vimc_streamer_pipeline_init(struct vimc_stream *stream,
>  	}
>  
>  	vimc_streamer_stream_terminate(cved);
> -	vimc_streamer_pipeline_terminate(stream);
> +	kref_put(&stream->refcount, vimc_streamer_pipeline_terminate);
>  	return -EINVAL;
>  }
>  
> @@ -298,7 +293,7 @@ int vimc_streamer_s_stream(struct vimc_stream *stream,
>  			ret = PTR_ERR(stream->kthread);
>  			dev_err(ved->dev, "kthread_run failed with %d\n", ret);
>  			vimc_streamer_stream_terminate(ved);
> -			vimc_streamer_pipeline_terminate(stream);
> +			kref_put(&stream->refcount, vimc_streamer_pipeline_terminate);
>  		}
>  
>  	} else {
> @@ -306,7 +301,7 @@ int vimc_streamer_s_stream(struct vimc_stream *stream,
>  			goto out;
>  
>  		vimc_streamer_stream_terminate(ved);
> -		vimc_streamer_pipeline_terminate(stream);
> +		kref_put(&stream->refcount, vimc_streamer_pipeline_terminate);
>  	}
>  out:
>  	mutex_unlock(&vimc_streamer_lock);
> diff --git a/drivers/media/test-drivers/vimc/vimc-streamer.h b/drivers/media/test-drivers/vimc/vimc-streamer.h
> index 3bb6731b8d4d..533c88675362 100644
> --- a/drivers/media/test-drivers/vimc/vimc-streamer.h
> +++ b/drivers/media/test-drivers/vimc/vimc-streamer.h
> @@ -18,6 +18,7 @@
>  /**
>   * struct vimc_stream - struct that represents a stream in the pipeline
>   *
> + * @refcount:		kref object associated with stream struct

What does it track though?

We know it's associated with the stream struct because it's in the
vimc_stream struct.



>   * @pipe:		the media pipeline object associated with this stream
>   * @ved_pipeline:	array containing all the entities participating in the
>   * 			stream. The order is from a video device (usually a

The fact that this comment still says "all entities participating in the
stream" worries me a little, as I think now the Streamer is dealing with
multiple streams.

I think we need to be really clear with the differences of objects and
terminology.

For instance I think the current terms are something like this:

Streamer: Responsible for managing processing from a sensor device
through all entities.

Stream: A flow of frames to a single capture video device node.

Pipeline: All entities used within the vimc streamer ?

(I'm not sure if those are right, I'm writing down what my current
interpretations are, so if someone wants to/can clarify - please do).



> @@ -32,6 +33,7 @@
>   * process frames for the stream.
>   */
>  struct vimc_stream {
> +	struct kref refcount;
>  	struct media_pipeline pipe;
>  	struct vimc_ent_device *ved_pipeline[VIMC_STREAMER_PIPELINE_MAX_SIZE];
>  	unsigned int pipe_size;
> 

-- 
Regards
--
Kieran

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