Re: [PATCH v3 4/9] media: vimc: Separate starting stream from pipeline initialisation

[Kaaira Gupta <kgupta@es.iitr.ac.in>]

On Wed, Sep 02, 2020 at 10:56:46AM +0100, Kieran Bingham wrote:
> Hi Kaaira, Dafna,
> 
> On 28/08/2020 21:37, Dafna Hirschfeld wrote:
> > Hi,
> > 
> > Am 21.08.20 um 23:01 schrieb Kaaira Gupta:
> >> Hi,
> >>
> >> On Fri, Aug 21, 2020 at 05:11:23PM +0200, Dafna Hirschfeld wrote:
> >>>
> >>>
> >>> Am 19.08.20 um 20:04 schrieb Kaaira Gupta:
> >>>> Separate the process of initialising pipeline array from starting
> >>>> streaming for all entities in path of a stream. This is needed because
> >>>> multiple streams can stream, but only one pipeline object is needed.
> >>>>
> >>>> Process frames only for those entities in a pipeline which are
> >>>> streaming. This is known through their use counts.
> >>>>
> >>>> Signed-off-by: Kaaira Gupta <kgupta@es.iitr.ac.in>
> >>>> ---
> >>>>    .../media/test-drivers/vimc/vimc-streamer.c   | 95
> >>>> ++++++++++++++++---
> >>>>    1 file changed, 83 insertions(+), 12 deletions(-)
> >>>>
> >>>> diff --git a/drivers/media/test-drivers/vimc/vimc-streamer.c
> >>>> b/drivers/media/test-drivers/vimc/vimc-streamer.c
> >>>> index c1644d69686d..cc40ecabe95a 100644
> >>>> --- a/drivers/media/test-drivers/vimc/vimc-streamer.c
> >>>> +++ b/drivers/media/test-drivers/vimc/vimc-streamer.c
> >>>> @@ -40,33 +40,30 @@ static void
> >>>> vimc_streamer_pipeline_terminate(struct vimc_stream *stream)
> >>>>    }
> >>>>    /**
> >>>> - * vimc_streamer_pipeline_init - Initializes the stream structure
> >>>> + * vimc_streamer_stream_start - Starts streaming for all entities
> >>>> + * in a stream
> >>>>     *
> >>>> - * @stream: the pointer to the stream structure to be initialized
> >>>>     * @ved:    the pointer to the vimc entity initializing the stream
> >>>>     *
> >>>> - * Initializes the stream structure. Walks through the entity graph to
> >>>> - * construct the pipeline used later on the streamer thread.
> >>>> - * Calls vimc_streamer_s_stream() to enable stream in all entities of
> >>>> - * the pipeline.
> >>>> + * Walks through the entity graph to call vimc_streamer_s_stream()
> >>>> + * to enable stream in all entities in path of a stream.
> >>>>     *
> >>>>     * Return: 0 if success, error code otherwise.
> >>>>     */
> >>>> -static int vimc_streamer_pipeline_init(struct vimc_stream *stream,
> >>>> -                       struct vimc_ent_device *ved)
> >>>> +static int vimc_streamer_stream_start(struct vimc_stream *stream,
> >>>> +                      struct vimc_ent_device *ved)
> >>>>    {
> >>>>        struct media_entity *entity;
> >>>>        struct video_device *vdev;
> >>>>        struct v4l2_subdev *sd;
> >>>> +    int stream_size = 0;
> >>>>        int ret = 0;
> >>>> -    stream->pipe_size = 0;
> >>>> -    while (stream->pipe_size < VIMC_STREAMER_PIPELINE_MAX_SIZE) {
> >>>> +    while (stream_size < VIMC_STREAMER_PIPELINE_MAX_SIZE) {
> >>>>            if (!ved) {
> >>>>                vimc_streamer_pipeline_terminate(stream);
> >>>>                return -EINVAL;
> >>>>            }
> >>>> -        stream->ved_pipeline[stream->pipe_size++] = ved;
> >>>>            if (is_media_entity_v4l2_subdev(ved->ent)) {
> >>>>                sd = media_entity_to_v4l2_subdev(ved->ent);
> >>>> @@ -104,6 +101,73 @@ static int vimc_streamer_pipeline_init(struct
> >>>> vimc_stream *stream,
> >>>>                            entity);
> >>>>                ved = video_get_drvdata(vdev);
> >>>>            }
> >>>> +        stream_size++;
> >>>> +    }
> >>>> +
> >>>> +    vimc_streamer_pipeline_terminate(stream);
> >>>> +    return -EINVAL;
> >>>> +}
> >>>> +
> >>>> +/**
> >>>> + * vimc_streamer_pipeline_init - Initialises pipeline and pipe size
> >>>> + *
> >>>> + * @stream: the pointer to the stream structure
> >>>> + * @ved:    the pointer to the vimc entity initializing the stream
> >>>> pipeline
> 
> Which entity is this? Is it the start, or the end of the pipeline? I.e.
> the sensor? or the capture ?

It is the capture, I will add it to the documentation..thanks

> 
> >>>> + *
> >>>> + * Walks through the entity graph to initialise ved_pipeline and
> >>>> updates
> >>>> + * pipe_size too.
> >>>> + *
> >>>> + * Return: 0 if success, error code otherwise.
> >>>> + */
> >>>> +static int vimc_streamer_pipeline_init(struct vimc_stream *stream,
> >>>> +                       struct vimc_ent_device *ved)
> >>>> +{
> >>>> +    struct media_entity *entity;
> >>>> +    struct media_device *mdev;
> >>>> +    struct media_graph graph;
> >>>> +    struct video_device *vdev;
> >>>> +    struct v4l2_subdev *sd;
> >>>> +    int ret;
> >>>> +
> >>>> +    entity = ved->ent;
> >>>> +    mdev = entity->graph_obj.mdev;
> >>>> +
> >>>> +    ret = media_graph_walk_init(&graph, mdev);
> >>>> +    if (ret)
> >>>> +        return ret;
> >>>> +
> >>>> +    media_graph_walk_start(&graph, entity);
> >>>> +
> >>>> +    /*
> >>>> +     * Start pipeline array initialisation from RAW Capture only to
> >>>> get
> >>>> +     * entities in the correct order of their frame processing.
> >>>> +     */
> >>>> +    if (!strncmp(entity->name, "RGB", 3)) {
> >>>
> >>> I don't understand this condition, way is it good for?
> >>
> >> I have explained that later in the reply
> 
> Matching on entity names is a bit awkward, as they could be changed I
> guess quite easily, and easily missed in this string matching.

Agreed, I need to think of a better way to prevent this

> 
> I haven't fully understood this code block yet to work out if there's
> another way we could do this though, but reading ahead I see there might
> be a way to 'walk the graph' on a per-stream basis which might be a good
> way of factoring this path.
> 
> Although there still needs to be a construction of the paths available
> to a stream which splits from the sensor.
> 
> 
> >>
> >>>
> >>> I think the function should be generic and not assume names of entities
> >>> or specific topology.
> >>
> >> It doesn't assume the topology, rather it is in place just to make sure
> >> that the entities in ved_pipeline are in correct order.
> >>
> >>>
> >>>
> >>>> +        entity = media_graph_walk_next(&graph);
> >>>> +        mdev = entity->graph_obj.mdev;
> >>>> +        media_graph_walk_cleanup(&graph);
> >>>> +
> >>>> +        ret = media_graph_walk_init(&graph, mdev);
> >>>> +        if (ret)
> >>>> +            return ret;
> >>>> +        media_graph_walk_start(&graph, entity);
> > 
> > Hi, can you explain what this code does?
> > Why does it start the search in the next entity?
> > 
> >>>> +    }
> >>>> +
> >>>> +    while (stream->pipe_size < VIMC_STREAMER_PIPELINE_MAX_SIZE) {
> >>>> +        if (is_media_entity_v4l2_subdev(entity)) {
> >>>> +            sd = media_entity_to_v4l2_subdev(entity);
> >>>> +            ved = v4l2_get_subdevdata(sd);
> >>>> +        } else {
> >>>> +            vdev = container_of(entity, struct video_device, entity);
> >>>> +            ved = video_get_drvdata(vdev);
> >>>> +        }
> >>>> +        stream->ved_pipeline[stream->pipe_size++] = ved;
> >>>> +        entity = media_graph_walk_next(&graph);
> >>>> +
> >>>> +        if (!strcmp(entity->name,
> >>>> stream->ved_pipeline[0]->ent->name)) {
> >>>
> >>> I also don't understand this condition
> >>>
> >>>> +            media_graph_walk_cleanup(&graph);
> >>>> +            return 0;
> >>>> +        }
> >>>>        }
> >>>
> >>> It is not clear what this function does, it looks like it adds to
> >>> 'ved_pipeline'
> >>> all entities that are connected to the video node, in addition to the
> >>> entities
> >>> that where there from previous calls, so some entities appear several
> >>> times.
> >>
> >> This function returns all the entities in a pipe, weather they are
> >> streaming or not. For example, if only the RAW Capture 1 streams, or
> >> RGB/YUB capture streams, or both stream..in all three cases ved_pipeline
> >> will have the same entities, in exactly same order, and all will occur
> >> just once.
> >> Since media_graph_walk goes to each node of the graph, it returns back
> >> to the first one (as its a graph), hence the last condition, ie,
> >>
> >>     if (!strcmp(entity->name, stream->ved_pipeline[0]->ent->name)) {
> >>
> >> makes sure that the first entity is not added again to the array.
> >>
> >> First condition, ie
> >>
> >>     if (!strncmp(entity->name, "RGB", 3)) {
> >>
> >> Just makes sure that the search starts at RGB capture only. This is
> >> because, in case of any other video node, the order of entities, as you
> >> have mentioned later in the mail, will not be desirable, ie it won't
> >> start at sensor and end at captures. So this condition just takes care
> >> that all the entities in ved_pipeline array are in correct order
> >> (starting at sensor, ending at captures).
> > 
> > It is better to compare to the whole name of the entity to make it more
> > clear.
> > Also I think it is better to document that this function is called only
> > upon the
> > first streaming node.
> 
> If this doesn't end up refactored with other helpers, then indeed a few
> comments might help the readabilty here. The distinctions of each
> re-initialisation of the graph walk are hard to interpret the purpose.
> 
> 
> 
> > 
> > I still think this function should be independent of the topology.
> > Maybe you can use Helen's patch that allow walking a graph only opposite
> > to the link direction: https://patchwork.kernel.org/patch/11564899/
> > This ensures that the Sensor will be first in the graph walk. Then the
> > streaming thread
> > iterates the ved_pipeline from 0 upwards and not from 'pipe_size'
> > downwards.
> 
> Being able to use a direct helper to walk the pipeline cleanly sounds
> promising indeed.
> 
> I suspect at some point int he next patches though - I'm going to see
> something that needs to have full visibility of all paths enabled from
> the sensor, as I think I recall that the thread will then process all
> (enabled) entities in a single pass.

Yes, that exactly is the problem :( This helper (that dafna has shared)
can walk through one path, while the thread (which processes the frames)
needs to view all the entites in all connected paths

> --
> Kieran
> 
> 
> > 
> > Thanks,
> > Dafna
> > 
> > 
> > 
> >>
> >> Thanks,
> >> Kaaira
> >>
> >>>
> >>> I think there is no need to use the graph walk here but to access the
> >>> source entity
> >>> in each iteration, the way done in vimc_streamer_stream_start
> >>> also.
> >>> I think the code should iterate here until it reaches an entity that
> >>> is already streaming,
> >>> this means that the entity is already in the `ved_pipeline`, also you
> >>> should make sure
> >>> that the sensor is the first entity that process a frame, therefore
> >>> the sensor should be
> >>> at the end/start of the list of entities. Generally each entity
> >>> should appear exactly once
> >>> in the 'ved_pipeline' array and the entities should be ordered such
> >>> that when calling 'process_frame'
> >>> on one entity should be after calling 'process_frame' on its source
> >>> entity.
> >>> maybe it is easyer to implement if 'ved_pipeline' is a linked list.
> >>>
> >>> Thanks,
> >>> Dafna
> >>>
> >>>>        vimc_streamer_pipeline_terminate(stream);
> >>>> @@ -138,8 +202,11 @@ static int vimc_streamer_thread(void *data)
> >>>>            for (i = stream->pipe_size - 1; i >= 0; i--) {
> >>>>                ved = stream->ved_pipeline[i];
> >>>> -            ret = ved->process_frame(ved);
> >>>> +            if (atomic_read(&ved->use_count) == 0)
> >>>> +                continue;
> >>>> +
> >>>> +            ret = ved->process_frame(ved);
> >>>>                if (ret)
> >>>>                    break;
> >>>>            }
> >>>> @@ -179,6 +246,10 @@ int vimc_streamer_s_stream(struct vimc_stream
> >>>> *stream,
> >>>>            if (stream->kthread)
> >>>>                return 0;
> >>>> +        ret = vimc_streamer_stream_start(stream, ved);
> >>>> +        if (ret)
> >>>> +            return ret;
> >>>> +
> >>>>            ret = vimc_streamer_pipeline_init(stream, ved);
> >>>>            if (ret)
> >>>>                return ret;
> >>>>
> 
> -- 
> Regards
> --
> Kieran