PM: runtime: add tracepoint for runtime_status changes

Existing runtime PM ftrace events (`rpm_suspend`, `rpm_resume`,
`rpm_return_int`) offer limited visibility into the exact timing of device
runtime power state transitions, particularly when asynchronous operations
are involved. When the `rpm_suspend` or `rpm_resume` functions are invoked
with the `RPM_ASYNC` flag, a return value of 0 i.e., success merely
indicates that the device power state request has been queued, not that
the device has yet transitioned.

A new ftrace event, `rpm_status`, is introduced. This event directly logs
the `power.runtime_status` value of a device whenever it changes providing
granular tracking of runtime power state transitions regardless of
synchronous or asynchronous `rpm_suspend` / `rpm_resume` usage.

Signed-off-by: Vilas Bhat <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/base/power/runtime.c

···
 static void __update_runtime_status(struct device *dev, enum rpm_status status)
 {
 	update_pm_runtime_accounting(dev);
+	trace_rpm_status(dev, status);
 	dev->power.runtime_status = status;
 }
 

include/trace/events/rpm.h

···
 		__entry->ret)
 );
 
+#define RPM_STATUS_STRINGS \
+	EM(RPM_INVALID, "RPM_INVALID") \
+	EM(RPM_ACTIVE, "RPM_ACTIVE") \
+	EM(RPM_RESUMING, "RPM_RESUMING") \
+	EM(RPM_SUSPENDED, "RPM_SUSPENDED") \
+	EMe(RPM_SUSPENDING, "RPM_SUSPENDING")
+
+/* Enums require being exported to userspace, for user tool parsing. */
+#undef EM
+#undef EMe
+#define EM(a, b)	TRACE_DEFINE_ENUM(a);
+#define EMe(a, b)	TRACE_DEFINE_ENUM(a);
+
+RPM_STATUS_STRINGS
+
+/*
+ * Now redefine the EM() and EMe() macros to map the enums to the strings that
+ * will be printed in the output.
+ */
+#undef EM
+#undef EMe
+#define EM(a, b)	{ a, b },
+#define EMe(a, b)	{ a, b }
+
+TRACE_EVENT(rpm_status,
+	TP_PROTO(struct device *dev, enum rpm_status status),
+	TP_ARGS(dev, status),
+
+	TP_STRUCT__entry(
+		__string(name,	dev_name(dev))
+		__field(int,	status)
+	),
+
+	TP_fast_assign(
+		__assign_str(name, dev_name(dev));
+		__entry->status = status;
+	),
+
+	TP_printk("%s status=%s", __get_str(name),
+		__print_symbolic(__entry->status, RPM_STATUS_STRINGS))
+);
+
 #endif /* _TRACE_RUNTIME_POWER_H */
 
 /* This part must be outside protection */