PM / sleep: add configurable delay for pm_test

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@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Reviewed-by: Kevin Cernekee <cernekee@chromium.org>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 6 insertions, 4 deletions

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