PM: hibernate: add configurable delay for pm_test

Turn the default 5 second test delay for hibernation into a
configurable module parameter, so users can determine how
long to wait in this pseudo-hibernate state before resuming
the system.

The configurable delay parameter has been added for suspend, so
add an analogous one for hibernation.

Example (wait 30 seconds);

# echo 30 > /sys/module/hibernate/parameters/pm_test_delay
# echo core > /sys/power/pm_test

Signed-off-by: Zihuan Zhang <[e-mail]>
Reviewed-by: Randy Dunlap <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/admin-guide/kernel-parameters.txt

···
 				lz4: Select LZ4 compression algorithm to
 				compress/decompress hibernation image.
 
+	hibernate.pm_test_delay=
+			[HIBERNATION]
+			Sets the number of seconds to remain in a hibernation test
+			mode before resuming the system (see
+			/sys/power/pm_test). Only available when CONFIG_PM_DEBUG
+			is set. Default value is 5.
+
 	highmem=nn[KMG]	[KNL,BOOT,EARLY] forces the highmem zone to have an exact
 			size of <nn>. This works even on boxes that have no
 			highmem otherwise. This also works to reduce highmem

kernel/power/hibernate.c

···
 EXPORT_SYMBOL(system_entering_hibernation);
 
 #ifdef CONFIG_PM_DEBUG
+static unsigned int pm_test_delay = 5;
+module_param(pm_test_delay, uint, 0644);
+MODULE_PARM_DESC(pm_test_delay,
+		 "Number of seconds to wait before resuming from hibernation test");
 static void hibernation_debug_sleep(void)
 {
-	pr_info("debug: Waiting for 5 seconds.\n");
-	mdelay(5000);
+	pr_info("hibernation debug: Waiting for %d second(s).\n",
+		pm_test_delay);
+	mdelay(pm_test_delay * 1000);
 }
 
 static int hibernation_test(int level)