PM / timekeeping: Print debug messages when requested

The messages printed by tk_debug_account_sleep_time() are basically
useful for system sleep debugging, so print them only when the other
debug messages from the core suspend/hibernate code are enabled.

While at it, make it clear that the messages from
tk_debug_account_sleep_time() are about timekeeping suspend
duration, because in general timekeeping may be suspeded and
resumed for multiple times during one system suspend-resume cycle.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

include/linux/suspend.h

@@ -492,16 +492,22 @@ static inline void unlock_system_sleep(void) {}
 
 #ifdef CONFIG_PM_SLEEP_DEBUG
 extern bool pm_print_times_enabled;
-extern __printf(1, 2) void pm_pr_dbg(const char *fmt, ...);
+extern __printf(2, 3) void __pm_pr_dbg(bool defer, const char *fmt, ...);
 #else
 #define pm_print_times_enabled	(false)
 
 #include <linux/printk.h>
 
-#define pm_pr_dbg(fmt, ...) \
+#define __pm_pr_dbg(defer, fmt, ...) \
 	no_printk(KERN_DEBUG fmt, ##__VA_ARGS__)
 #endif
 
+#define pm_pr_dbg(fmt, ...) \
+	__pm_pr_dbg(false, fmt, ##__VA_ARGS__)
+
+#define pm_deferred_pr_dbg(fmt, ...) \
+	__pm_pr_dbg(true, fmt, ##__VA_ARGS__)
+
 #ifdef CONFIG_PM_AUTOSLEEP
 
 /* kernel/power/autosleep.c */

kernel/power/main.c

@@ -388,13 +388,14 @@ static ssize_t pm_debug_messages_store(struct kobject *kobj,
 power_attr(pm_debug_messages);
 
 /**
- * pm_pr_dbg - Print a suspend debug message to the kernel log.
+ * __pm_pr_dbg - Print a suspend debug message to the kernel log.
+ * @defer: Whether or not to use printk_deferred() to print the message.
  * @fmt: Message format.
  *
  * The message will be emitted if enabled through the pm_debug_messages
  * sysfs attribute.
  */
-void pm_pr_dbg(const char *fmt, ...)
+void __pm_pr_dbg(bool defer, const char *fmt, ...)
 {
 	struct va_format vaf;
 	va_list args;
@@ -407,6 +408,9 @@ void pm_pr_dbg(const char *fmt, ...)
 	vaf.fmt = fmt;
 	vaf.va = &args;
 
+	if (defer)
+		printk_deferred(KERN_DEBUG "PM: %pV", &vaf);
+	else
 		printk(KERN_DEBUG "PM: %pV", &vaf);
 
 	va_end(args);

kernel/time/timekeeping_debug.c

@@ -19,6 +19,7 @@
 #include <linux/init.h>
 #include <linux/kernel.h>
 #include <linux/seq_file.h>
+#include <linux/suspend.h>
 #include <linux/time.h>
 
 #include "timekeeping_internal.h"
@@ -75,7 +76,7 @@ void tk_debug_account_sleep_time(struct timespec64 *t)
 	int bin = min(fls(t->tv_sec), NUM_BINS-1);
 
 	sleep_time_bin[bin]++;
-	printk_deferred(KERN_INFO "Suspended for %lld.%03lu seconds\n",
+	pm_deferred_pr_dbg("Timekeeping suspended for %lld.%03lu seconds\n",
 			   (s64)t->tv_sec, t->tv_nsec / NSEC_PER_MSEC);
 }