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Wed, 2 Sep 2020 02:56:54 -0700 (PDT) Received: from [192.168.0.20] (cpc89244-aztw30-2-0-cust3082.18-1.cable.virginm.net [86.31.172.11]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 6947B9CC; Wed, 2 Sep 2020 11:56:50 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1599040611; bh=5XdTleSlo5fDp/4fIAvShbXcIJMbvnb+7bQA75IkzBs=; h=Reply-To:Subject:To:Cc:References:From:Date:In-Reply-To:From; b=ktz3hBVwmMhGVPCIoKLfNxn73NZNLpAywHBbIa4veQto9zyqiCkNYruRJo4bIlU67 /dW2w0Cpqz21FXyKML211w1QtRJqKh0adJTL/tqyyZsUXZfsGTxf0jqVDeTUFu5uya gpJWTg42lLZVoCStw/sxl9oW68Bta8uymKte5nx8= Reply-To: kieran.bingham@ideasonboard.com Subject: Re: [PATCH v3 4/9] media: vimc: Separate starting stream from pipeline initialisation To: Dafna Hirschfeld , Kaaira Gupta Cc: Helen Koike , Shuah Khan , Mauro Carvalho Chehab , linux-media@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200819180442.11630-1-kgupta@es.iitr.ac.in> <20200819180442.11630-5-kgupta@es.iitr.ac.in> <20200821210123.GA28410@kaaira-HP-Pavilion-Notebook> From: Kieran Bingham Autocrypt: addr=kieran.bingham@ideasonboard.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 >>>> --- >>>>    .../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 ? >>>> + * >>>> + * 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. 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. -- 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