Re: [PATCH v3 2/4] media: v4l2-common: add helper functions to call s_stream() callbacks

[Niklas Söderlund]

Hi Helen,

Thanks for your work.

On 2020-04-14 22:30:42 -0300, Helen Koike wrote:
> Add v4l2_pipeline_stream_{enable,disable} helper functions to iterate
> through the subdevices in a given stream (i.e following links from sink
> to source) and call .s_stream() callback.
> 
> Add stream_count on the subdevice object for simultaneous streaming from
> different video devices which shares subdevices.
> 
> Prevent calling .s_stream(true) if it was already called previously by
> another stream.
> 
> Prevent calling .s_stream(false) from one stream when there are still
> others active.
> 
> If .s_stream(true) fails, call .s_stream(false) in the reverse order.
> 
> Signed-off-by: Helen Koike <helen.koike@xxxxxxxxxxxxx>
> ---
> 
> Changes in v3:
> - re-write helpers to use media walkers as in v1, but with
> v4l2_pipeline_subdevs_get() to reverse the order we call s_stream(true)
> in subdevices.
> - rename size to max_size (and update docs) in v4l2_pipeline_subdevs_get() to
> reflect the meaning of the argument.
> - add if defined(CONFIG_MEDIA_CONTROLLER) around helpers
> 
> Changes in v2:
> - re-write helpers to not use media walkers
> 
>  drivers/media/v4l2-core/v4l2-common.c | 125 ++++++++++++++++++++++++++
>  include/media/v4l2-common.h           |  43 +++++++++
>  include/media/v4l2-subdev.h           |   2 +
>  3 files changed, 170 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index 9e8eb45a5b03c..2f991a1a57d7c 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -442,3 +442,128 @@ int v4l2_fill_pixfmt(struct v4l2_pix_format *pixfmt, u32 pixelformat,
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(v4l2_fill_pixfmt);
> +
> +#if defined(CONFIG_MEDIA_CONTROLLER)
> +
> +/*
> + * v4l2_pipeline_subdevs_get - Assemble a list of subdevices in a pipeline
> + * @subdevs: the array to be filled.
> + * @max_size: max number of elements that can fit in subdevs array.
> + *
> + * Walk from a video node, following links from sink to source and fill the
> + * array with subdevices in the path.
> + * The walker performs a depth-first traversal, which means that, in a topology
> + * sd1->sd2->sd3->vdev, sd1 will be the first element placed in the array.
> + *
> + * Return the number of subdevices filled in the array.
> + */
> +static int v4l2_pipeline_subdevs_get(struct video_device *vdev,
> +				     struct media_pipeline *pipe,
> +				     struct v4l2_subdev **subdevs,
> +				     unsigned int max_size)
> +{
> +	struct media_entity *entity = &vdev->entity;
> +	struct media_device *mdev = entity->graph_obj.mdev;
> +	int idx = 0;
> +	int ret;
> +
> +	mutex_lock(&mdev->graph_mutex);
> +
> +	if (!pipe->streaming_count) {
> +		ret = media_graph_walk_init(&pipe->graph, mdev);
> +		if (ret) {
> +			mutex_unlock(&mdev->graph_mutex);
> +			return ret;
> +		}
> +	}

This confuses me a bit. Why is this conditional on streaming_count ?  
Looking how it's used in mc-entity.c the count is also 
increased/decreased with this pattern.

Would it make sens to create a local 'struct media_graph graph' here and 
always init and clean it up ?

> +
> +	media_graph_walk_start(&pipe->graph, entity);
> +
> +	while ((entity = media_graph_walk_next_stream(&pipe->graph))) {
> +		if (!is_media_entity_v4l2_subdev(entity))
> +			continue;
> +		if (WARN_ON(idx >= max_size)) {
> +			mutex_unlock(&mdev->graph_mutex);
> +			return -EINVAL;
> +		}
> +		subdevs[idx++] = media_entity_to_v4l2_subdev(entity);
> +	}
> +
> +	if (!pipe->streaming_count)
> +		media_graph_walk_cleanup(&pipe->graph);
> +
> +	mutex_unlock(&mdev->graph_mutex);
> +
> +	return idx;
> +}
> +
> +__must_check int v4l2_pipeline_stream_enable(struct video_device *vdev,
> +					     struct media_pipeline *pipe)
> +{
> +	struct media_device *mdev = vdev->entity.graph_obj.mdev;
> +	struct v4l2_subdev *subdevs[MEDIA_ENTITY_ENUM_MAX_DEPTH];
> +	struct v4l2_subdev *sd;
> +	int i, size, ret;
> +
> +	size = v4l2_pipeline_subdevs_get(vdev, pipe,
> +					 subdevs, ARRAY_SIZE(subdevs));
> +	if (size <= 0)
> +		return size;
> +
> +	/* Call s_stream() in reverse order to enable sensors last */
> +	for (i = size - 1; i >= 0; i--) {
> +		sd = subdevs[i];
 +		if (sd->stream_count++)
> +			continue;
> +		dev_dbg(mdev->dev,
> +			"enabling stream for '%s'\n", sd->entity.name);
> +		ret = v4l2_subdev_call(sd, video, s_stream, true);
> +		if (ret && ret != -ENOIOCTLCMD) {
> +			sd->stream_count = 0;
> +			goto err_stream_disable;
> +		}
> +	}
> +
> +	return 0;
> +
> +err_stream_disable:
> +	for (i++; i < size; i++) {
> +		sd = subdevs[i];
> +		if (--sd->stream_count)
> +			continue;
> +		dev_dbg(mdev->dev,
> +			"disabling stream for '%s'\n", sd->entity.name);
> +		v4l2_subdev_call(sd, video, s_stream, false);
> +	};
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_pipeline_stream_enable);
> +
> +void v4l2_pipeline_stream_disable(struct video_device *vdev,
> +				  struct media_pipeline *pipe)
> +{
> +	struct media_device *mdev = vdev->entity.graph_obj.mdev;
> +	struct v4l2_subdev *subdevs[MEDIA_ENTITY_ENUM_MAX_DEPTH];
> +	unsigned int i;
> +	int size;
> +
> +	size = v4l2_pipeline_subdevs_get(vdev, pipe,
> +					 subdevs, ARRAY_SIZE(subdevs));
> +	if (WARN_ON(size < 0))
> +		return;
> +
> +	/* Call s_stream() in order to disable sensors first */
> +	for (i = 0; i < size; i++) {
> +		struct v4l2_subdev *sd = subdevs[i];
> +
> +		if (--sd->stream_count)
> +			continue;
> +		dev_dbg(mdev->dev,
> +			"disabling stream for '%s'\n", sd->entity.name);
> +		v4l2_subdev_call(sd, video, s_stream, false);

small nit, maybe this can be extracted to a helper as the code is 
duplicated here and in the error path v4l2_pipeline_stream_enable ?

> +	}
> +}
> +EXPORT_SYMBOL_GPL(v4l2_pipeline_stream_disable);
> +
> +#endif /* CONFIG_MEDIA_CONTROLLER */
> diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> index 150ee16ebd811..dc46812120cdc 100644
> --- a/include/media/v4l2-common.h
> +++ b/include/media/v4l2-common.h
> @@ -539,4 +539,47 @@ static inline void v4l2_buffer_set_timestamp(struct v4l2_buffer *buf,
>  	buf->timestamp.tv_usec = ts.tv_nsec / NSEC_PER_USEC;
>  }
>  
> +#if defined(CONFIG_MEDIA_CONTROLLER)
> +
> +/**
> + * v4l2_pipeline_stream_enable - Call .s_stream(true) callbacks in the stream
> + * @vdev: Starting video device.
> + * @pipe: Pipeline this entity belongs to.
> + *
> + * Call .s_stream(true) callback in all the subdevices participating in the
> + * stream, i.e. following links from sink to source.
> + *
> + * .s_stream(true) is also called from sink to source, i.e. in a topology
> + * sd1->sd2->sd3->vdev, .s_stream(true) of sd3 is called first.
> + *
> + * Calls to this function can be nested, in which case the same number of
> + * v4l2_pipeline_stream_disable() calls will be required to disable streaming
> + * through subdevices in the pipeline.
> + * The  pipeline pointer must be identical for all nested calls to
> + * v4l2_pipeline_stream_enable().
> + */
> +__must_check int v4l2_pipeline_stream_enable(struct video_device *vdev,
> +					     struct media_pipeline *pipe);
> +
> +/**
> + * v4l2_pipeline_stream_disable - Call .s_stream(false) callbacks in the stream
> + * @vdev: Starting video device.
> + * @pipe: Pipeline this entity belongs to.
> + *
> + * Call .s_stream(false) callback in all the subdevices participating in the
> + * stream, i.e. following links from sink to source.
> + *
> + * s_stream(false) is called in a reverse order from
> + * v4l2_pipeline_stream_enable(), i.e. in a topology sd1->sd2->sd3->vdev,
> + * .s_stream(false) of sd1 is called first.
> + *
> + * If multiple calls to v4l2_pipeline_stream_enable() have been made, the same
> + * number of calls to this function are required to disable streaming through
> + * subdevices in the pipeline.
> + */
> +void v4l2_pipeline_stream_disable(struct video_device *vdev,
> +				  struct media_pipeline *pipe);
> +
> +#endif /* CONFIG_MEDIA_CONTROLLER */
> +
>  #endif /* V4L2_COMMON_H_ */
> diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
> index a4848de598521..20f913a9f70c5 100644
> --- a/include/media/v4l2-subdev.h
> +++ b/include/media/v4l2-subdev.h
> @@ -838,6 +838,7 @@ struct v4l2_subdev_platform_data {
>   * @subdev_notifier: A sub-device notifier implicitly registered for the sub-
>   *		     device using v4l2_device_register_sensor_subdev().
>   * @pdata: common part of subdevice platform data
> + * @stream_count: Stream count for the subdevice.
>   *
>   * Each instance of a subdev driver should create this struct, either
>   * stand-alone or embedded in a larger struct.
> @@ -869,6 +870,7 @@ struct v4l2_subdev {
>  	struct v4l2_async_notifier *notifier;
>  	struct v4l2_async_notifier *subdev_notifier;
>  	struct v4l2_subdev_platform_data *pdata;
> +	unsigned int stream_count;
>  };
>  
>  
> -- 
> 2.26.0
> 

-- 
Regards,
Niklas Söderlund