Coresight: Add an interface for supporting ETM3/4 Context ID tracing

If PID namespace is enabled, everytime users configure the Context ID
register to trace the specific process, there needs to be a translation
between the real PID seen from the kernel and VPID seen from the
namespace in which the user's process resides .

This patch just adds the translation interface for ETMs.

Signed-off-by: Chunyan Zhang <zhang.chunyan@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/coresight.h

@@ -248,4 +248,24 @@ static inline struct coresight_platform_data *of_get_coresight_platform_data(
 	struct device *dev, struct device_node *node) { return NULL; }
 #endif
 
+#ifdef CONFIG_PID_NS
+static inline unsigned long
+coresight_vpid_to_pid(unsigned long vpid)
+{
+	struct task_struct *task = NULL;
+	unsigned long pid = 0;
+
+	rcu_read_lock();
+	task = find_task_by_vpid(vpid);
+	if (task)
+		pid = task_pid_nr(task);
+	rcu_read_unlock();
+
+	return pid;
+}
+#else
+static inline unsigned long
+coresight_vpid_to_pid(unsigned long vpid) { return vpid; }
+#endif
+
 #endif