[PATCH v3] PM / sleep: add configurable delay for pm_test

From: Brian Norris
Date: Mon Feb 23 2015 - 00:17:03 EST

When CONFIG_PM_DEBUG=y, we provide a sysfs file (/sys/power/pm_test) for
selecting one of a few suspend test modes, where rather than entering a
full suspend state, the kernel will perform some subset of suspend
steps, wait 5 seconds, and then resume back to normal operation.

This mode is useful for (among other things) observing the state of the
system just before entering a sleep mode, for debugging or analysis
purposes. However, a constant 5 second wait is not sufficient for some
sorts of analysis; for example, on an SoC, one might want to use
external tools to probe the power states of various on-chip controllers
or clocks.

This patch turns this 5 second delay into a configurable module
parameter, so users can determine how long to wait in this
pseudo-suspend state before resuming the system.

Example (wait 30 seconds);

# echo 30 > /sys/module/suspend/parameters/pm_test_delay
# echo core > /sys/power/pm_test
# time echo mem > /sys/power/state
[ 17.583625] suspend debug: Waiting for 30 second(s).
real 0m30.381s
user 0m0.017s
sys 0m0.080s

Signed-off-by: Brian Norris <computersforpeace@xxxxxxxxx>
Acked-by: Pavel Machek <pavel@xxxxxx>
Reviewed-by: Kevin Cernekee <cernekee@xxxxxxxxxxxx>
Acked-by: Florian Fainelli <f.fainelli@xxxxxxxxx>
v3: - document in a few more places

v2: - make this a module param instead of an explicit sysfs file
- drop the for loop; mdelay() does the same loop internally
- decrease +36 lines of code and +2 lines of doc, to +6 lines of code and
+2 lines of doc

Documentation/kernel-parameters.txt | 7 +++++++
Documentation/power/basic-pm-debugging.txt | 10 ++++++----
kernel/power/suspend.c | 13 +++++++++++--
3 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 176d4fe4f076..0b8a1fd0d08d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3433,6 +3433,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
improve throughput, but will also increase the
amount of memory reserved for use by the client.

+ suspend.pm_test_delay=
+ Sets the number of seconds to remain in a suspend test
+ mode before resuming the system (see
+ /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
+ is set. Default value is 5.
[KNL] Enable accounting of swap in memory resource
controller if no parameter or 1 is given or disable
diff --git a/Documentation/power/basic-pm-debugging.txt b/Documentation/power/basic-pm-debugging.txt
index edeecd447d23..b96098ccfe69 100644
--- a/Documentation/power/basic-pm-debugging.txt
+++ b/Documentation/power/basic-pm-debugging.txt
@@ -75,12 +75,14 @@ you should do the following:
# echo platform > /sys/power/disk
# echo disk > /sys/power/state

-Then, the kernel will try to freeze processes, suspend devices, wait 5 seconds,
-resume devices and thaw processes. If "platform" is written to
+Then, the kernel will try to freeze processes, suspend devices, wait a few
+seconds (5 by default, but configurable by the suspend.pm_test_delay module
+parameter), resume devices and thaw processes. If "platform" is written to
/sys/power/pm_test , then after suspending devices the kernel will additionally
invoke the global control methods (eg. ACPI global control methods) used to
-prepare the platform firmware for hibernation. Next, it will wait 5 seconds and
-invoke the platform (eg. ACPI) global methods used to cancel hibernation etc.
+prepare the platform firmware for hibernation. Next, it will wait a
+configurable number of seconds and invoke the platform (eg. ACPI) global
+methods used to cancel hibernation etc.

Writing "none" to /sys/power/pm_test causes the kernel to switch to the normal
hibernation/suspend operations. Also, when open for reading, /sys/power/pm_test
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index c347e3ce3a55..aee23dab0a55 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -28,6 +28,7 @@
#include <linux/ftrace.h>
#include <trace/events/power.h>
#include <linux/compiler.h>
+#include <linux/moduleparam.h>

#include "power.h"

@@ -204,12 +205,20 @@ static bool platform_suspend_again(suspend_state_t state)
suspend_ops->suspend_again() : false;

+static unsigned int pm_test_delay = 5;
+module_param(pm_test_delay, uint, 0644);
+ "Number of seconds to wait before resuming from suspend test");
static int suspend_test(int level)
if (pm_test_level == level) {
- printk(KERN_INFO "suspend debug: Waiting for 5 seconds.\n");
- mdelay(5000);
+ printk(KERN_INFO "suspend debug: Waiting for %d second(s).\n",
+ pm_test_delay);
+ mdelay(pm_test_delay * 1000);
return 1;
#endif /* !CONFIG_PM_DEBUG */

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