coresight: associating path with session rather than tracer

When using the Coresight framework from the sysFS interface a
tracer is always handling a single session and as such, a path
can be associated with a tracer.  But when supporting multiple
session per tracer there is no guarantee that sessions will always
have the same path from source to sink.

This patch is removing the automatic association between path and
tracers.  The building of a path and enablement of the components
in the path are decoupled, allowing for the association of a path
with a session rather than a tracer.

To keep backward functionality with the current sysFS access methods
a per-cpu place holder is used to keep a handle on the path built when
tracers are enabled.  Lastly APIs to build paths and enable tracers are
made public so that other subsystem can interact with the Coresight
framework.
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/coresight/coresight-priv.h

@@ -52,6 +52,11 @@ static inline void CS_UNLOCK(void __iomem *addr)
 	} while (0);
 }
 
+void coresight_disable_path(struct list_head *path);
+int coresight_enable_path(struct list_head *path);
+struct list_head *coresight_build_path(struct coresight_device *csdev);
+void coresight_release_path(struct list_head *path);
+
 #ifdef CONFIG_CORESIGHT_SOURCE_ETM3X
 extern int etm_readl_cp14(u32 off, unsigned int *val);
 extern int etm_writel_cp14(u32 off, u32 val);

include/linux/coresight.h

@@ -152,7 +152,6 @@ struct coresight_connection {
 		by @coresight_ops.
  * @dev:	The device entity associated to this component.
  * @refcnt:	keep track of what is in use.
- * @path_link:	link of current component into the path being enabled.
  * @orphan:	true if the component has connections that haven't been linked.
  * @enable:	'true' if component is currently part of an active path.
  * @activated:	'true' only if a _sink_ has been activated.  A sink can be
@@ -168,7 +167,6 @@ struct coresight_device {
 	const struct coresight_ops *ops;
 	struct device dev;
 	atomic_t *refcnt;
-	struct list_head path_link;
 	bool orphan;
 	bool enable;	/* true only if configured as part of a path */
 	bool activated;	/* true only if a sink is part of a path */