Re: [PATCH 3/5] v4l: Add generic pipeline power management code

[Hans Verkuil <hverkuil@xs4all.nl>]

On 01/27/16 14:50, Sakari Ailus wrote:
> When the Media controller framework was merged, it was decided not to add
> pipeline power management code for it was not seen generic. As a result, a
> number of drivers have copied the same piece of code, with same bugfixes
> done to them at different points of time (or not at all).
> 
> Add these functions to V4L2. Their use is optional for drivers.
> 
> Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> ---
>  drivers/media/v4l2-core/v4l2-common.c | 174 ++++++++++++++++++++++++++++++++++
>  include/media/v4l2-common.h           |  37 ++++++++

I think I would prefer to see a v4l2-mc.c source rather than adding it to common.
Since this is specific to both v4l2 and MC it only has to be compiled
if both config options are set.

Besides, I think we need to move more common mc code to such a file.

Regards,

	Hans

>  2 files changed, 211 insertions(+)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-common.c b/drivers/media/v4l2-core/v4l2-common.c
> index 5b80850..0e063a9 100644
> --- a/drivers/media/v4l2-core/v4l2-common.c
> +++ b/drivers/media/v4l2-core/v4l2-common.c
> @@ -405,3 +405,177 @@ void v4l2_get_timestamp(struct timeval *tv)
>  	tv->tv_usec = ts.tv_nsec / NSEC_PER_USEC;
>  }
>  EXPORT_SYMBOL_GPL(v4l2_get_timestamp);
> +
> +/* -----------------------------------------------------------------------------
> + * Pipeline power management
> + *
> + * Entities must be powered up when part of a pipeline that contains at least
> + * one open video device node.
> + *
> + * To achieve this use the entity use_count field to track the number of users.
> + * For entities corresponding to video device nodes the use_count field stores
> + * the users count of the node. For entities corresponding to subdevs the
> + * use_count field stores the total number of users of all video device nodes
> + * in the pipeline.
> + *
> + * The v4l2_pipeline_pm_use() function must be called in the open() and
> + * close() handlers of video device nodes. It increments or decrements the use
> + * count of all subdev entities in the pipeline.
> + *
> + * To react to link management on powered pipelines, the link setup notification
> + * callback updates the use count of all entities in the source and sink sides
> + * of the link.
> + */
> +
> +/*
> + * pipeline_pm_use_count - Count the number of users of a pipeline
> + * @entity: The entity
> + *
> + * Return the total number of users of all video device nodes in the pipeline.
> + */
> +static int pipeline_pm_use_count(struct media_entity *entity,
> +	struct media_entity_graph *graph)
> +{
> +	int use = 0;
> +
> +	media_entity_graph_walk_start(graph, entity);
> +
> +	while ((entity = media_entity_graph_walk_next(graph))) {
> +		if (is_media_entity_v4l2_io(entity))
> +			use += entity->use_count;
> +	}
> +
> +	return use;
> +}
> +
> +/*
> + * pipeline_pm_power_one - Apply power change to an entity
> + * @entity: The entity
> + * @change: Use count change
> + *
> + * Change the entity use count by @change. If the entity is a subdev update its
> + * power state by calling the core::s_power operation when the use count goes
> + * from 0 to != 0 or from != 0 to 0.
> + *
> + * Return 0 on success or a negative error code on failure.
> + */
> +static int pipeline_pm_power_one(struct media_entity *entity, int change)
> +{
> +	struct v4l2_subdev *subdev;
> +	int ret;
> +
> +	subdev = is_media_entity_v4l2_subdev(entity)
> +	       ? media_entity_to_v4l2_subdev(entity) : NULL;
> +
> +	if (entity->use_count == 0 && change > 0 && subdev != NULL) {
> +		ret = v4l2_subdev_call(subdev, core, s_power, 1);
> +		if (ret < 0 && ret != -ENOIOCTLCMD)
> +			return ret;
> +	}
> +
> +	entity->use_count += change;
> +	WARN_ON(entity->use_count < 0);
> +
> +	if (entity->use_count == 0 && change < 0 && subdev != NULL)
> +		v4l2_subdev_call(subdev, core, s_power, 0);
> +
> +	return 0;
> +}
> +
> +/*
> + * pipeline_pm_power - Apply power change to all entities in a pipeline
> + * @entity: The entity
> + * @change: Use count change
> + *
> + * Walk the pipeline to update the use count and the power state of all non-node
> + * entities.
> + *
> + * Return 0 on success or a negative error code on failure.
> + */
> +static int pipeline_pm_power(struct media_entity *entity, int change,
> +	struct media_entity_graph *graph)
> +{
> +	struct media_entity *first = entity;
> +	int ret = 0;
> +
> +	if (!change)
> +		return 0;
> +
> +	media_entity_graph_walk_start(graph, entity);
> +
> +	while (!ret && (entity = media_entity_graph_walk_next(graph)))
> +		if (is_media_entity_v4l2_subdev(entity))
> +			ret = pipeline_pm_power_one(entity, change);
> +
> +	if (!ret)
> +		return ret;
> +
> +	media_entity_graph_walk_start(graph, first);
> +
> +	while ((first = media_entity_graph_walk_next(graph))
> +	       && first != entity)
> +		if (is_media_entity_v4l2_subdev(first))
> +			pipeline_pm_power_one(first, -change);
> +
> +	return ret;
> +}
> +
> +int v4l2_pipeline_pm_use(struct media_entity *entity, int use)
> +{
> +	struct media_device *mdev = entity->graph_obj.mdev;
> +	int change = use ? 1 : -1;
> +	int ret;
> +
> +	mutex_lock(&mdev->graph_mutex);
> +
> +	/* Apply use count to node. */
> +	entity->use_count += change;
> +	WARN_ON(entity->use_count < 0);
> +
> +	/* Apply power change to connected non-nodes. */
> +	ret = pipeline_pm_power(entity, change, &mdev->pm_count_walk);
> +	if (ret < 0)
> +		entity->use_count -= change;
> +
> +	mutex_unlock(&mdev->graph_mutex);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_pipeline_pm_use);
> +
> +int v4l2_pipeline_link_notify(struct media_link *link, u32 flags,
> +			      unsigned int notification)
> +{
> +	struct media_entity_graph *graph = &link->graph_obj.mdev->pm_count_walk;
> +	struct media_entity *source = link->source->entity;
> +	struct media_entity *sink = link->sink->entity;
> +	int source_use;
> +	int sink_use;
> +	int ret = 0;
> +
> +	source_use = pipeline_pm_use_count(source, graph);
> +	sink_use = pipeline_pm_use_count(sink, graph);
> +
> +	if (notification == MEDIA_DEV_NOTIFY_POST_LINK_CH &&
> +	    !(flags & MEDIA_LNK_FL_ENABLED)) {
> +		/* Powering off entities is assumed to never fail. */
> +		pipeline_pm_power(source, -sink_use, graph);
> +		pipeline_pm_power(sink, -source_use, graph);
> +		return 0;
> +	}
> +
> +	if (notification == MEDIA_DEV_NOTIFY_PRE_LINK_CH &&
> +		(flags & MEDIA_LNK_FL_ENABLED)) {
> +
> +		ret = pipeline_pm_power(source, sink_use, graph);
> +		if (ret < 0)
> +			return ret;
> +
> +		ret = pipeline_pm_power(sink, source_use, graph);
> +		if (ret < 0)
> +			pipeline_pm_power(source, -sink_use, graph);
> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(v4l2_pipeline_link_notify);
> diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
> index 1cc0c5b..0c23940 100644
> --- a/include/media/v4l2-common.h
> +++ b/include/media/v4l2-common.h
> @@ -189,4 +189,41 @@ const struct v4l2_frmsize_discrete *v4l2_find_nearest_format(
>  
>  void v4l2_get_timestamp(struct timeval *tv);
>  
> +/**
> + * v4l2_pipeline_pm_use - Update the use count of an entity
> + * @entity: The entity
> + * @use: Use (1) or stop using (0) the entity
> + *
> + * Update the use count of all entities in the pipeline and power entities on or
> + * off accordingly.
> + *
> + * This function is intended to be called in video node open (use ==
> + * 1) and release (use == 0). It uses struct media_entity.use_count to
> + * track the power status. The use of this function should be paired
> + * with v4l2_pipeline_link_notify().
> + *
> + * Return 0 on success or a negative error code on failure. Powering entities
> + * off is assumed to never fail. No failure can occur when the use parameter is
> + * set to 0.
> + */
> +int v4l2_pipeline_pm_use(struct media_entity *entity, int use);
> +
> +
> +/**
> + * v4l2_pipeline_link_notify - Link management notification callback
> + * @link: The link
> + * @flags: New link flags that will be applied
> + * @notification: The link's state change notification type (MEDIA_DEV_NOTIFY_*)
> + *
> + * React to link management on powered pipelines by updating the use count of
> + * all entities in the source and sink sides of the link. Entities are powered
> + * on or off accordingly. The use of this function should be paired
> + * with v4l2_pipeline_pm_use().
> + *
> + * Return 0 on success or a negative error code on failure. Powering entities
> + * off is assumed to never fail. This function will not fail for disconnection
> + * events.
> + */
> +int v4l2_pipeline_link_notify(struct media_link *link, u32 flags,
> +			      unsigned int notification);
>  #endif /* V4L2_COMMON_H_ */
>