[power] Improve suspend functions.

- Implement pm_suspend(), which is callable from anywhere in the kernel, 
  and takes one of 

  	PM_SUSPEND_STANDBY
	PM_SUSPEND_MEM
	PM_SUSPEND_DISK

  and enters the appropriate state. 

- Change sysfs file to look for 

  "standby"
  "mem"
  "disk"

  for what state to enter (rather than 'suspend' and 'hibernate' for the 
  latter two). 

- Add pm_sem to block multiple suspend sequences happening at once. 

- Allocate a console and stop processes from common code before entering
  state.

- Add pm_power_down() callback for platform drivers to implement. Will be 
  called to actually enter the low-power state.

include/linux/pm.h

@@ -186,9 +186,31 @@ static inline void pm_dev_idle(struct pm_dev *dev) {}
 
 #endif /* CONFIG_PM */
 
+
+/*
+ * Callbacks for platform drivers to implement.
+ */
 extern void (*pm_idle)(void);
 extern void (*pm_power_off)(void);
 
+enum {
+	PM_SUSPEND_ON,
+	PM_SUSPEND_STANDBY,
+	PM_SUSPEND_MEM,
+	PM_SUSPEND_DISK,
+	PM_SUSPEND_MAX,
+};
+
+extern int (*pm_power_down)(u32 state);
+
+
+extern int pm_suspend(u32 state);
+
+
+/*
+ * Device power management
+ */
+
 struct device;
 
 struct dev_pm_info {

kernel/power/main.c

@@ -8,6 +8,7 @@
  *
  */
 
+#include <linux/suspend.h>
 #include <linux/kobject.h>
 #include <linux/string.h>
 #include <linux/errno.h>
@@ -15,42 +16,114 @@
 #include <linux/pm.h>
 
 
+int (*pm_power_down)(u32 state) = NULL;
 
-static int standby(void)
+
+static DECLARE_MUTEX(pm_sem);
+
+
+static int pm_suspend_standby(void)
 {
 	return 0;
 }
 
-static int suspend(void)
+static int pm_suspend_mem(void)
 {
 	return 0;
 }
 
-static int hibernate(void)
+static int pm_suspend_disk(void)
 {
 	return 0;
 }
 
 #define decl_state(_name) \
-	{ .name = __stringify(_name), .fn = _name }
+	{ .name = __stringify(_name), .fn = pm_suspend_##_name }
 
 struct pm_state {
 	char * name;
 	int (*fn)(void);
 } pm_states[] = {
-	decl_state(standby),
-	decl_state(suspend),
-	decl_state(hibernate),
+	[PM_SUSPEND_STANDBY]	= decl_state(standby),
+	[PM_SUSPEND_MEM]	= decl_state(mem),
+	[PM_SUSPEND_DISK]	= decl_state(disk),
 	{ NULL },
 };
 
 
+static int suspend_prepare(void)
+{
+	int error = 0;
+
+	pm_prepare_console();
+
+	if (freeze_processes()) {
+		thaw_processes();
+		error = -EAGAIN;
+		goto Done;
+	}
+
+ Done:
+	pm_restore_console();
+	return error;
+}
+
+static void suspend_finish(void)
+{
+	thaw_processes();
+	pm_restore_console();
+}
+
+
+/**
+ *	enter_state - Do common work of entering low-power state.
+ *	@state:		pm_state structure for state we're entering.
+ *
+ *	Make sure we're the only ones trying to enter a sleep state. Fail
+ *	if someone has beat us to it, since we don't want anything weird to
+ *	happen when we wake up.
+ *	Then, do the setup for suspend, enter the state, and cleaup (after
+ *	we've woken up).
+ */
+
 static int enter_state(struct pm_state * state)
 {
-	return state->fn();
+	int error;
+
+	if (down_trylock(&pm_sem))
+		return -EBUSY;
+
+	if (!pm_power_down) {
+		error = -EPERM;
+		goto Unlock;
+	}
+
+	if ((error = suspend_prepare()))
+		return error;
+
+	error = state->fn();
+	suspend_finish();
+ Unlock:
+	up(&pm_sem);
+	return error;
 }
 
 
+/**
+ *	pm_suspend - Externally visible function for suspending system.
+ *	@state:		Enumarted value of state to enter.
+ *
+ *	Determine whether or not value is within range, get state 
+ *	structure, and enter (above).
+ */
+
+int pm_suspend(u32 state)
+{
+	if (state > PM_SUSPEND_ON && state < PM_SUSPEND_MAX)
+		return enter_state(&pm_states[state]);
+	return -EINVAL;
+}
+
 
 decl_subsys(power,NULL,NULL);
 
@@ -69,8 +142,8 @@ static struct subsys_attribute _name##_attr = {	\
  *	state - control system power state.
  *
  *	show() returns what states are supported, which is hard-coded to
- *	'standby' (Power-On Suspend), 'suspend' (Suspend-to-RAM), and
- *	'hibernate' (Suspend-to-Disk).
+ *	'standby' (Power-On Suspend), 'mem' (Suspend-to-RAM), and
+ *	'disk' (Suspend-to-Disk).
  *
  *	store() accepts one of those strings, translates it into the 
  *	proper enumerated value, and initiates a suspend transition.
@@ -97,12 +170,13 @@ static ssize_t state_store(struct subsystem * s, const char * buf, size_t n)
 		*end = '\0';
 
 	for (state = &pm_states[0]; state; state++) {
-		if (!strcmp(buf,state->name))
+		if (state->name && !strcmp(buf,state->name))
 			break;
 	}
-	if (!state)
-		return -EINVAL;
-	error = enter_state(state);
+	if (state)
+		error = enter_state(state);
+	else
+		error = -EINVAL;
 	return error ? error : n;
 }