PM / sleep: Introduce command line argument for sleep state enumeration

On some systems the platform doesn't support neither
PM_SUSPEND_MEM nor PM_SUSPEND_STANDBY, so PM_SUSPEND_FREEZE is the
only available system sleep state.  However, some user space frameworks
only use the "mem" and (sometimes) "standby" sleep state labels, so
the users of those systems need to modify user space in order to be
able to use system suspend at all and that is not always possible.

For this reason, add a new kernel command line argument,
relative_sleep_states, allowing the users of those systems to change
the way in which the kernel assigns labels to system sleep states.
Namely, for relative_sleep_states=1, the "mem", "standby" and "freeze"
labels will enumerate the available system sleem states from the
deepest to the shallowest, respectively, so that "mem" is always
present in /sys/power/state and the other state strings may or may
not be presend depending on what is supported by the platform.

Update system sleep states documentation to reflect this change.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

2 files changed, 36 insertions, 8 deletions

diff --git a/kernel/power/main.c b/kernel/power/main.c
index 9f51f0ab3d8..573410d6647 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -279,14 +279,14 @@ static inline void pm_print_times_init(void) {}
 struct kobject *power_kobj;
 
 /**
- *	state - control system power state.
+ * state - control system sleep states.
  *
- *	show() returns what states are supported, which is hard-coded to
- *	'freeze' (Low-Power Idle), 'standby' (Power-On Suspend),
- *	'mem' (Suspend-to-RAM), and 'disk' (Suspend-to-Disk).
+ * show() returns available sleep state labels, which may be "mem", "standby",
+ * "freeze" and "disk" (hibernation).  See Documentation/power/states.txt for a
+ * description of what they mean.
  *
- *	store() accepts one of those strings, translates it into the
- *	proper enumerated value, and initiates a suspend transition.
+ * store() accepts one of those strings, translates it into the proper
+ * enumerated value, and initiates a suspend transition.
  */
 static ssize_t state_show(struct kobject *kobj, struct kobj_attribute *attr,
 			  char *buf)
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 00aca60904b..338a6f14797 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -78,6 +78,26 @@ static bool valid_state(suspend_state_t state)
 	return suspend_ops && suspend_ops->valid && suspend_ops->valid(state);
 }
 
+/*
+ * If this is set, the "mem" label always corresponds to the deepest sleep state
+ * available, the "standby" label corresponds to the second deepest sleep state
+ * available (if any), and the "freeze" label corresponds to the remaining
+ * available sleep state (if there is one).
+ */
+static bool relative_states;
+
+static int __init sleep_states_setup(char *str)
+{
+	relative_states = !strncmp(str, "1", 1);
+	if (relative_states) {
+		pm_states[PM_SUSPEND_MEM].state = PM_SUSPEND_FREEZE;
+		pm_states[PM_SUSPEND_FREEZE].state = 0;
+	}
+	return 1;
+}
+
+__setup("relative_sleep_states=", sleep_states_setup);
+
 /**
  * suspend_set_ops - Set the global suspend method table.
  * @ops: Suspend operations to use.
@@ -85,12 +105,20 @@ static bool valid_state(suspend_state_t state)
 void suspend_set_ops(const struct platform_suspend_ops *ops)
 {
 	suspend_state_t i;
+	int j = PM_SUSPEND_MAX - 1;
 
 	lock_system_sleep();
 
 	suspend_ops = ops;
-	for (i = PM_SUSPEND_STANDBY; i <= PM_SUSPEND_MEM; i++)
-		pm_states[i].state = valid_state(i) ? i : 0;
+	for (i = PM_SUSPEND_MEM; i >= PM_SUSPEND_STANDBY; i--)
+		if (valid_state(i))
+			pm_states[j--].state = i;
+		else if (!relative_states)
+			pm_states[j--].state = 0;
+
+	pm_states[j--].state = PM_SUSPEND_FREEZE;
+	while (j >= PM_SUSPEND_MIN)
+		pm_states[j--].state = 0;
 
 	unlock_system_sleep();
 }