Re: [PATCH v5 13/18] watchdog/hardlockup: Have the perf hardlockup use __weak functions more cleanly

The fact that there watchdog_hardlockup_enable(),
watchdog_hardlockup_disable(), and watchdog_hardlockup_probe() are
declared __weak means that the configured hardlockup detector can
define non-weak versions of those functions if it needs to. Instead of
doing this, the perf hardlockup detector hooked itself into the
default __weak implementation, which was a bit awkward. Clean this up.

quoted

From comments, it looks as if the original design was done because the

__weak function were expected to implemented by the architecture and
not by the configured hardlockup detector. This got awkward when we
tried to add the buddy lockup detector which was not arch-specific but
wanted to hook into those same functions.

This is not expected to have any functional impact.

@@ -187,27 +187,33 @@ static inline void watchdog_hardlockup_kick(void) { }
 #endif /* !CONFIG_HARDLOCKUP_DETECTOR_PERF */
 
 /*
- * These functions can be overridden if an architecture implements its
- * own hardlockup detector.
+ * These functions can be overridden based on the configured hardlockdup detector.
  *
  * watchdog_hardlockup_enable/disable can be implemented to start and stop when
- * softlockup watchdog start and stop. The arch must select the
+ * softlockup watchdog start and stop. The detector must select the
  * SOFTLOCKUP_DETECTOR Kconfig.
  */
-void __weak watchdog_hardlockup_enable(unsigned int cpu)
-{
-	hardlockup_detector_perf_enable();
-}
+void __weak watchdog_hardlockup_enable(unsigned int cpu) { }
 
-void __weak watchdog_hardlockup_disable(unsigned int cpu)
-{
-	hardlockup_detector_perf_disable();
-}
+void __weak watchdog_hardlockup_disable(unsigned int cpu) { }
 
 /* Return 0, if a hardlockup watchdog is available. Error code otherwise */
 int __weak __init watchdog_hardlockup_probe(void)
 {
-	return hardlockup_detector_perf_init();
+	/*
+	 * If CONFIG_HAVE_NMI_WATCHDOG is defined then an architecture
+	 * is assumed to have the hard watchdog available and we return 0.
+	 */
+	if (IS_ENABLED(CONFIG_HAVE_NMI_WATCHDOG))
+		return 0;
+
+	/*
+	 * Hardlockup detectors other than those using CONFIG_HAVE_NMI_WATCHDOG
+	 * are required to implement a non-weak version of this probe function
+	 * to tell whether they are available. If they don't override then
+	 * we'll return -ENODEV.
+	 */
+	return -ENODEV;
 }