[PATCH] swsusp: debugging

Add a swsusp debugging mode. This does everything that's needed for a suspend
except for actually suspending. So we can look in the log messages and work
out a) what code is being slow and b) which drivers are misbehaving.

(1)
# echo testproc > /sys/power/disk
# echo disk > /sys/power/state

This should turn off the non-boot CPU, freeze all processes, wait for 5
seconds and then thaw the processes and the CPU.

(2)
# echo test > /sys/power/disk
# echo disk > /sys/power/state

This should turn off the non-boot CPU, freeze all processes, shrink
memory, suspend all devices, wait for 5 seconds, resume the devices etc.

Cc: Pavel Machek <[e-mail]>
Cc: Stefan Seyfried <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/ABI/testing/sysfs-power

···
 		these states.
 
 What:		/sys/power/disk
-Date:		August 2006
+Date:		September 2006
 Contact:	Rafael J. Wysocki <[e-mail]>
 Description:
 		The /sys/power/disk file controls the operating mode of the
···
 		'reboot' - the memory image will be saved by the kernel and
 		the system will be rebooted.
 
+		Additionally, /sys/power/disk can be used to turn on one of the
+		two testing modes of the suspend-to-disk mechanism: 'testproc'
+		or 'test'.  If the suspend-to-disk mechanism is in the
+		'testproc' mode, writing 'disk' to /sys/power/state will cause
+		the kernel to disable nonboot CPUs and freeze tasks, wait for 5
+		seconds, unfreeze tasks and enable nonboot CPUs.  If it is in
+		the 'test' mode, writing 'disk' to /sys/power/state will cause
+		the kernel to disable nonboot CPUs and freeze tasks, shrink
+		memory, suspend devices, wait for 5 seconds, resume devices,
+		unfreeze tasks and enable nonboot CPUs.  Then, we are able to
+		look in the log messages and work out, for example, which code
+		is being slow and which device drivers are misbehaving.
+
 		The suspend-to-disk method may be chosen by writing to this
 		file one of the accepted strings:
 
···
 		'platform'
 		'shutdown'
 		'reboot'
+		'testproc'
+		'test'
 
 		It will only change to 'firmware' or 'platform' if the system
 		supports that.

Documentation/power/interface.txt

···
 that is known a priori. But, the user may choose 'shutdown' or
 'reboot' as alternatives. 
 
+Additionally, /sys/power/disk can be used to turn on one of the two testing
+modes of the suspend-to-disk mechanism: 'testproc' or 'test'.  If the
+suspend-to-disk mechanism is in the 'testproc' mode, writing 'disk' to
+/sys/power/state will cause the kernel to disable nonboot CPUs and freeze
+tasks, wait for 5 seconds, unfreeze tasks and enable nonboot CPUs.  If it is
+in the 'test' mode, writing 'disk' to /sys/power/state will cause the kernel
+to disable nonboot CPUs and freeze tasks, shrink memory, suspend devices, wait
+for 5 seconds, resume devices, unfreeze tasks and enable nonboot CPUs.  Then,
+we are able to look in the log messages and work out, for example, which code
+is being slow and which device drivers are misbehaving.
+
 Reading from this file will display what the mode is currently set
 to. Writing to this file will accept one of
 
···
        'platform'
        'shutdown'
        'reboot'
+       'testproc'
+       'test'
 
 It will only change to 'firmware' or 'platform' if the system supports
 it. 

include/linux/pm.h

···
 #define	PM_DISK_PLATFORM	((__force suspend_disk_method_t) 2)
 #define	PM_DISK_SHUTDOWN	((__force suspend_disk_method_t) 3)
 #define	PM_DISK_REBOOT		((__force suspend_disk_method_t) 4)
-#define	PM_DISK_MAX		((__force suspend_disk_method_t) 5)
+#define	PM_DISK_TEST		((__force suspend_disk_method_t) 5)
+#define	PM_DISK_TESTPROC	((__force suspend_disk_method_t) 6)
+#define	PM_DISK_MAX		((__force suspend_disk_method_t) 7)
 
 struct pm_ops {
 	suspend_disk_method_t pm_disk_mode;

kernel/power/disk.c

···
 
 static int prepare_processes(void)
 {
-	int error;
+	int error = 0;
 
 	pm_prepare_console();
 
···
 
 	if (freeze_processes()) {
 		error = -EBUSY;
+		goto thaw;
+	}
+
+	if (pm_disk_mode == PM_DISK_TESTPROC) {
+		printk("swsusp debug: Waiting for 5 seconds.\n");
+		mdelay(5000);
 		goto thaw;
 	}
 
···
 	if (error)
 		return error;
 
+	if (pm_disk_mode == PM_DISK_TESTPROC)
+		goto Thaw;
+
 	suspend_console();
 	error = device_suspend(PMSG_FREEZE);
 	if (error) {
 		resume_console();
 		printk("Some devices failed to suspend\n");
-		unprepare_processes();
-		return error;
+		goto Thaw;
+	}
+
+	if (pm_disk_mode == PM_DISK_TEST) {
+		printk("swsusp debug: Waiting for 5 seconds.\n");
+		mdelay(5000);
+		goto Done;
 	}
 
 	pr_debug("PM: snapshotting memory.\n");
···
 			power_down(pm_disk_mode);
 		else {
 			swsusp_free();
-			unprepare_processes();
-			return error;
+			goto Thaw;
 		}
-	} else
+	} else {
 		pr_debug("PM: Image restored successfully.\n");
+	}
 
 	swsusp_free();
  Done:
 	device_resume();
 	resume_console();
+ Thaw:
 	unprepare_processes();
 	return error;
 }
···
 	[PM_DISK_PLATFORM]	= "platform",
 	[PM_DISK_SHUTDOWN]	= "shutdown",
 	[PM_DISK_REBOOT]	= "reboot",
+	[PM_DISK_TEST]		= "test",
+	[PM_DISK_TESTPROC]	= "testproc",
 };
 
 /**
···
 		}
 	}
 	if (mode) {
-		if (mode == PM_DISK_SHUTDOWN || mode == PM_DISK_REBOOT)
+		if (mode == PM_DISK_SHUTDOWN || mode == PM_DISK_REBOOT ||
+		     mode == PM_DISK_TEST || mode == PM_DISK_TESTPROC) {
 			pm_disk_mode = mode;
-		else {
+		} else {
 			if (pm_ops && pm_ops->enter &&
 			    (mode == pm_ops->pm_disk_mode))
 				pm_disk_mode = mode;
 			else
 				error = -EINVAL;
 		}
-	} else
+	} else {
 		error = -EINVAL;
+	}
 
 	pr_debug("PM: suspend-to-disk mode set to '%s'\n",
 		 pm_disk_modes[mode]);