Re: [PATCH V3] coresight: Make sysFS functional on topologies with per core sink

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

Hi Linu,

On Tue, Aug 11, 2020 at 07:58:42AM +0530, Linu Cherian wrote:
> Coresight driver assumes sink is common across all the ETMs,
> and tries to build a path between ETM and the first enabled
> sink found using bus based search. This breaks sysFS usage
> on implementations that has multiple per core sinks in
> enabled state.
> 
> For this,
> - coresight_find_sink API is updated with an additional flag
>   so that it is able to return an enabled sink
> - coresight_get_enabled_sink API is updated to do a
>   connection based search, when a source reference is given.
> 
> Signed-off-by: Linu Cherian <lcherian@marvell.com>
> ---
> Applies on https://git.linaro.org/kernel/coresight.git/log/?h=next
> 
> Changes in V3:
> Fixed checkpatch issue.
> 
>  .../hwtracing/coresight/coresight-etm-perf.c  |  2 +-
>  drivers/hwtracing/coresight/coresight-priv.h  |  5 +-
>  drivers/hwtracing/coresight/coresight.c       | 51 +++++++++++++++++--
>  3 files changed, 51 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> index 1a3169e69bb1..25041d2654e3 100644
> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> @@ -223,7 +223,7 @@ static void *etm_setup_aux(struct perf_event *event, void **pages,
>  		id = (u32)event->attr.config2;
>  		sink = coresight_get_sink_by_id(id);
>  	} else {
> -		sink = coresight_get_enabled_sink(true);
> +		sink = coresight_get_enabled_sink(NULL, true);

It is time for this subsystem to move out of the prehistoric age.  Please remove
the call to coresight_get_enabled_sink() entirely.  In the change log you can
write that selecting a sink from sysfs is deprecated when using the perf
interface.  I will personally refactor the code if someone complains that it
broke their user space.

>  	}
>  
>  	mask = &event_data->mask;
> diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> index f2dc625ea585..010ed26db340 100644
> --- a/drivers/hwtracing/coresight/coresight-priv.h
> +++ b/drivers/hwtracing/coresight/coresight-priv.h
> @@ -148,10 +148,13 @@ static inline void coresight_write_reg_pair(void __iomem *addr, u64 val,
>  void coresight_disable_path(struct list_head *path);
>  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_enabled_sink(struct coresight_device *source, bool reset);
>  struct coresight_device *coresight_get_sink_by_id(u32 id);
>  struct coresight_device *
>  coresight_find_default_sink(struct coresight_device *csdev);
> +struct coresight_device *
> +coresight_find_enabled_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 e9c90f2de34a..ae69169c58d3 100644
> --- a/drivers/hwtracing/coresight/coresight.c
> +++ b/drivers/hwtracing/coresight/coresight.c
> @@ -566,6 +566,10 @@ static int coresight_enabled_sink(struct device *dev, const void *data)
>  
>  /**
>   * coresight_get_enabled_sink - returns the first enabled sink found on the bus
> + * When a source reference is given, enabled sink is found using connection based
> + * search.
> + *
> + * @source: Coresight source device reference
>   * @deactivate:	Whether the 'enable_sink' flag should be reset
>   *
>   * When operated from perf the deactivate parameter should be set to 'true'.
> @@ -576,10 +580,21 @@ static int coresight_enabled_sink(struct device *dev, const void *data)
>   * parameter should be set to 'false', hence mandating users to explicitly
>   * clear the flag.
>   */
> -struct coresight_device *coresight_get_enabled_sink(bool deactivate)
> +struct coresight_device *
> +coresight_get_enabled_sink(struct coresight_device *source, bool deactivate)

This code was written during a time when all sources were able to reach a sink,
something that is no longer the case.  Starting from a source is the right way
to go.

>  {
>  	struct device *dev = NULL;
> +	struct coresight_device *sink;
> +
> +	if (!source)
> +		goto bus_search;

Return NULL if a source was not given.

> +	sink = coresight_find_enabled_sink(source);
> +	if (sink && deactivate)
> +		sink->activated = false;
> +
> +	return sink;

You get credits for trying to re-use code but in this case I would like to avoid
modifying coresight_find_sink() to keep it as simple as possible.  I suggest to
copy the for() loop in coresight_find_sink() and stop the search when the first
activated sink is found.  It will introduce a little bit of code duplication but
I think we will gain a lot in maintainability.

>  
> +bus_search:
>  	dev = bus_find_device(&coresight_bustype, NULL, &deactivate,
>  			      coresight_enabled_sink);

Get rid of this.  You can also get rid of the 'deactivate' parameter since it
won't be used anymore. 

Let me know if you have questions.

Thanks,
Mathieu

>  
> @@ -828,6 +843,7 @@ coresight_select_best_sink(struct coresight_device *sink, int *depth,
>   *
>   * @csdev: source / current device to check.
>   * @depth: [in] search depth of calling dev, [out] depth of found sink.
> + * @enabled: flag to search only enabled sinks
>   *
>   * This will walk the connection path from a source (ETM) till a suitable
>   * sink is encountered and return that sink to the original caller.
> @@ -839,7 +855,7 @@ coresight_select_best_sink(struct coresight_device *sink, int *depth,
>   * 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)
> +coresight_find_sink(struct coresight_device *csdev, int *depth, bool enabled)
>  {
>  	int i, curr_depth = *depth + 1, found_depth = 0;
>  	struct coresight_device *found_sink = NULL;
> @@ -862,7 +878,8 @@ coresight_find_sink(struct coresight_device *csdev, int *depth)
>  
>  		child_dev = csdev->pdata->conns[i].child_dev;
>  		if (child_dev)
> -			sink = coresight_find_sink(child_dev, &child_depth);
> +			sink = coresight_find_sink(child_dev, &child_depth,
> +						   enabled);
>  
>  		if (sink)
>  			found_sink = coresight_select_best_sink(found_sink,
> @@ -872,6 +889,10 @@ coresight_find_sink(struct coresight_device *csdev, int *depth)
>  	}
>  
>  return_def_sink:
> +	/* Check if we need to return an enabled sink */
> +	if (enabled && found_sink)
> +		if (!found_sink->activated)
> +			found_sink = NULL;
>  	/* return found sink and depth */
>  	if (found_sink)
>  		*depth = found_depth;
> @@ -901,10 +922,30 @@ coresight_find_default_sink(struct coresight_device *csdev)
>  
>  	/* 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);
> +		csdev->def_sink = coresight_find_sink(csdev, &depth, false);
>  	return csdev->def_sink;
>  }
>  
> +/**
> + * coresight_find_enabled_sink: Find the suitable enabled 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.
> + *
> + * Used in cases where the CoreSight user (sysfs) has selected a sink.
> + */
> +struct coresight_device *
> +coresight_find_enabled_sink(struct coresight_device *csdev)
> +{
> +	int depth = 0;
> +
> +	/* look for the enabled sink */
> +	return coresight_find_sink(csdev, &depth, true);
> +}
> +
>  static int coresight_remove_sink_ref(struct device *dev, void *data)
>  {
>  	struct coresight_device *sink = data;
> @@ -992,7 +1033,7 @@ int coresight_enable(struct coresight_device *csdev)
>  	 * Search for a valid sink for this session but don't reset the
>  	 * "enable_sink" flag in sysFS.  Users get to do that explicitly.
>  	 */
> -	sink = coresight_get_enabled_sink(false);
> +	sink = coresight_get_enabled_sink(csdev, false);
>  	if (!sink) {
>  		ret = -EINVAL;
>  		goto out;
> -- 
> 2.25.1
> 

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