Re: [PATCH v4 2/5] coresight: Add default sink selection to CoreSight base

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Tue, May 26, 2020 at 11:46:39AM +0100, Mike Leach wrote:
> Adds a method to select a suitable sink connected to a given source.
> 
> In cases where no sink is defined, the coresight_find_default_sink
> routine can search from a given source, through the child connections
> until a suitable sink is found.
> 
> The suitability is defined in by the sink coresight_dev_subtype on the
> CoreSight device, and the distance from the source by counting
> connections.
> 
> Higher value subtype is preferred - where these are equal, shorter
> distance from source is used as a tie-break.
> 
> This allows for default sink to be discovered were none is specified
> (e.g. perf command line)
> 
> Signed-off-by: Mike Leach <mike.leach@linaro.org>

Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>

Leo has also added a RB for this patch, please add it on when you rebase on
v5.8-rc1.

> ---
>  drivers/hwtracing/coresight/coresight-priv.h |   2 +
>  drivers/hwtracing/coresight/coresight.c      | 136 +++++++++++++++++++
>  include/linux/coresight.h                    |   3 +
>  3 files changed, 141 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> index 36c943ae94d5..f2dc625ea585 100644
> --- a/drivers/hwtracing/coresight/coresight-priv.h
> +++ b/drivers/hwtracing/coresight/coresight-priv.h
> @@ -150,6 +150,8 @@ int coresight_enable_path(struct list_head *path, u32 mode, void *sink_data);
>  struct coresight_device *coresight_get_sink(struct list_head *path);
>  struct coresight_device *coresight_get_enabled_sink(bool reset);
>  struct coresight_device *coresight_get_sink_by_id(u32 id);
> +struct coresight_device *
> +coresight_find_default_sink(struct coresight_device *csdev);
>  struct list_head *coresight_build_path(struct coresight_device *csdev,
>  				       struct coresight_device *sink);
>  void coresight_release_path(struct list_head *path);
> diff --git a/drivers/hwtracing/coresight/coresight.c b/drivers/hwtracing/coresight/coresight.c
> index f3efbb3b2b4d..7632d060e25d 100644
> --- a/drivers/hwtracing/coresight/coresight.c
> +++ b/drivers/hwtracing/coresight/coresight.c
> @@ -769,6 +769,142 @@ void coresight_release_path(struct list_head *path)
>  	path = NULL;
>  }
>  
> +/* return true if the device is a suitable type for a default sink */
> +static inline bool coresight_is_def_sink_type(struct coresight_device *csdev)
> +{
> +	/* sink & correct subtype */
> +	if (((csdev->type == CORESIGHT_DEV_TYPE_SINK) ||
> +	     (csdev->type == CORESIGHT_DEV_TYPE_LINKSINK)) &&
> +	    (csdev->subtype.sink_subtype >= CORESIGHT_DEV_SUBTYPE_SINK_BUFFER))
> +		return true;
> +	return false;
> +}
> +
> +/**
> + * coresight_select_best_sink - return the best sink for use as default from
> + * the two provided.
> + *
> + * @sink:	current best sink.
> + * @depth:      search depth where current sink was found.
> + * @new_sink:	new sink for comparison with current sink.
> + * @new_depth:  search depth where new sink was found.
> + *
> + * Sinks prioritised according to coresight_dev_subtype_sink, with only
> + * subtypes CORESIGHT_DEV_SUBTYPE_SINK_BUFFER or higher being used.
> + *
> + * Where two sinks of equal priority are found, the sink closest to the
> + * source is used (smallest search depth).
> + *
> + * return @new_sink & update @depth if better than @sink, else return @sink.
> + */
> +static struct coresight_device *
> +coresight_select_best_sink(struct coresight_device *sink, int *depth,
> +			   struct coresight_device *new_sink, int new_depth)
> +{
> +	bool update = false;
> +
> +	if (!sink) {
> +		/* first found at this level */
> +		update = true;
> +	} else if (new_sink->subtype.sink_subtype >
> +		   sink->subtype.sink_subtype) {
> +		/* found better sink */
> +		update = true;
> +	} else if ((new_sink->subtype.sink_subtype ==
> +		    sink->subtype.sink_subtype) &&
> +		   (*depth > new_depth)) {
> +		/* found same but closer sink */
> +		update = true;
> +	}
> +
> +	if (update)
> +		*depth = new_depth;
> +	return update ? new_sink : sink;
> +}
> +
> +/**
> + * coresight_find_sink - recursive function to walk trace connections from
> + * source to find a suitable default sink.
> + *
> + * @csdev: source / current device to check.
> + * @depth: [in] search depth of calling dev, [out] depth of found sink.
> + *
> + * This will walk the connection path from a source (ETM) till a suitable
> + * sink is encountered and return that sink to the original caller.
> + *
> + * If current device is a plain sink return that & depth, otherwise recursively
> + * call child connections looking for a sink. Select best possible using
> + * coresight_select_best_sink.
> + *
> + * return best sink found, or NULL if not found at this node or child nodes.
> + */
> +static struct coresight_device *
> +coresight_find_sink(struct coresight_device *csdev, int *depth)
> +{
> +	int i, curr_depth = *depth + 1, found_depth = 0;
> +	struct coresight_device *found_sink = NULL;
> +
> +	if (coresight_is_def_sink_type(csdev)) {
> +		found_depth = curr_depth;
> +		found_sink = csdev;
> +		if (csdev->type == CORESIGHT_DEV_TYPE_SINK)
> +			goto return_def_sink;
> +		/* look past LINKSINK for something better */
> +	}
> +
> +	/*
> +	 * Not a sink we want - or possible child sink may be better.
> +	 * recursively explore each port found on this element.
> +	 */
> +	for (i = 0; i < csdev->pdata->nr_outport; i++) {
> +		struct coresight_device *child_dev, *sink = NULL;
> +		int child_depth = curr_depth;
> +
> +		child_dev = csdev->pdata->conns[i].child_dev;
> +		if (child_dev)
> +			sink = coresight_find_sink(child_dev, &child_depth);
> +
> +		if (sink)
> +			found_sink = coresight_select_best_sink(found_sink,
> +								&found_depth,
> +								sink,
> +								child_depth);
> +	}
> +
> +return_def_sink:
> +	/* return found sink and depth */
> +	if (found_sink)
> +		*depth = found_depth;
> +	return found_sink;
> +}
> +
> +/**
> + * coresight_find_default_sink: Find a sink suitable for use as a
> + * default sink.
> + *
> + * @csdev: starting source to find a connected sink.
> + *
> + * Walks connections graph looking for a suitable sink to enable for the
> + * supplied source. Uses CoreSight device subtypes and distance from source
> + * to select the best sink.
> + *
> + * If a sink is found, then the default sink for this device is set and
> + * will be automatically used in future.
> + *
> + * Used in cases where the CoreSight user (perf / sysfs) has not selected a
> + * sink.
> + */
> +struct coresight_device *
> +coresight_find_default_sink(struct coresight_device *csdev)
> +{
> +	int depth = 0;
> +
> +	/* look for a default sink if we have not found for this device */
> +	if (!csdev->def_sink)
> +		csdev->def_sink = coresight_find_sink(csdev, &depth);
> +	return csdev->def_sink;
> +}
> +
>  /** coresight_validate_source - make sure a source has the right credentials
>   *  @csdev:	the device structure for a source.
>   *  @function:	the function this was called from.
> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> index 84dc695e87d4..58fffdecdbfd 100644
> --- a/include/linux/coresight.h
> +++ b/include/linux/coresight.h
> @@ -48,6 +48,7 @@ enum coresight_dev_subtype_sink {
>  	CORESIGHT_DEV_SUBTYPE_SINK_NONE,
>  	CORESIGHT_DEV_SUBTYPE_SINK_PORT,
>  	CORESIGHT_DEV_SUBTYPE_SINK_BUFFER,
> +	CORESIGHT_DEV_SUBTYPE_SINK_SYSMEM,
>  };
>  
>  enum coresight_dev_subtype_link {
> @@ -182,6 +183,7 @@ struct coresight_sysfs_link {
>   *		happens when a source has been selected and a path is enabled
>   *		from source to that sink.
>   * @ea:		Device attribute for sink representation under PMU directory.
> + * @def_sink:	cached reference to default sink found for this device.
>   * @ect_dev:	Associated cross trigger device. Not part of the trace data
>   *		path or connections.
>   * @nr_links:   number of sysfs links created to other components from this
> @@ -200,6 +202,7 @@ struct coresight_device {
>  	/* sink specific fields */
>  	bool activated;	/* true only if a sink is part of a path */
>  	struct dev_ext_attribute *ea;
> +	struct coresight_device *def_sink;
>  	/* cross trigger handling */
>  	struct coresight_device *ect_dev;
>  	/* sysfs links between components */
> -- 
> 2.17.1
> 

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