PM: introduce set_target method in pm_ops

Commit 52ade9b3b97fd3bea42842a056fe0786c28d0555 changed the suspend code
ordering to execute pm_ops->prepare() after the device model per-device
.suspend() calls in order to fix some ACPI-related issues. Unfortunately, it
broke the at91 platform which assumed that pm_ops->prepare() would be called
before suspending devices.

at91 used pm_ops->prepare() to get notified of the target system sleep state,
so that it could use this information while suspending devices. However, with
the current suspend code ordering pm_ops->prepare() is called too late for
this purpose. Thus, at91 needs an additional method in 'struct pm_ops' that
will be used for notifying the platform of the target system sleep state.
Moreover, in the future such a method will also be needed by ACPI.

This patch adds the .set_target() method to 'struct pm_ops' and makes the
suspend code call it, if implemented, before executing the device model
per-device .suspend() calls. It also modifies the at91 code to use
pm_ops->set_target() instead of pm_ops->prepare().

Signed-off-by: Rafael J. Wysocki <[e-mail]>
Acked-by: David Brownell <[e-mail]>
Cc: Pavel Machek <[e-mail]>
Cc: Johannes Berg <[e-mail]>
Cc: Len Brown <[e-mail]>
Cc: Greg KH <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/arm/mach-at91/pm.c

···
 /*
  * Called after processes are frozen, but before we shutdown devices.
  */
-static int at91_pm_prepare(suspend_state_t state)
+static int at91_pm_set_target(suspend_state_t state)
 {
 	target_state = state;
 	return 0;
···
 
 static struct pm_ops at91_pm_ops ={
 	.valid		= at91_pm_valid_state,
-	.prepare	= at91_pm_prepare,
+	.set_target	= at91_pm_set_target,
 	.enter		= at91_pm_enter,
 };
 

include/linux/pm.h

···
 #define PM_SUSPEND_MAX		((__force suspend_state_t) 4)
 
 /**
- * struct pm_ops - Callbacks for managing platform dependent suspend states.
- * @valid: Callback to determine whether the given state can be entered.
- *	Valid states are advertised in /sys/power/state but can still
- *	be rejected by prepare or enter if the conditions aren't right.
- *	There is a %pm_valid_only_mem function available that can be assigned
- *	to this if you only implement mem sleep.
+ * struct pm_ops - Callbacks for managing platform dependent system sleep
+ *	states.
  *
- * @prepare: Prepare the platform for the given suspend state. Can return a
- *	negative error code if necessary.
+ * @valid: Callback to determine if given system sleep state is supported by
+ *	the platform.
+ *	Valid (ie. supported) states are advertised in /sys/power/state.  Note
+ *	that it still may be impossible to enter given system sleep state if the
+ *	conditions aren't right.
+ *	There is the %pm_valid_only_mem function available that can be assigned
+ *	to this if the platform only supports mem sleep.
  *
- * @enter: Enter the given suspend state, must be assigned. Can return a
- *	negative error code if necessary.
+ * @set_target: Tell the platform which system sleep state is going to be
+ *	entered.
+ *	@set_target() is executed right prior to suspending devices.  The
+ *	information conveyed to the platform code by @set_target() should be
+ *	disregarded by the platform as soon as @finish() is executed and if
+ *	@prepare() fails.  If @set_target() fails (ie. returns nonzero),
+ *	@prepare(), @enter() and @finish() will not be called by the PM core.
+ *	This callback is optional.  However, if it is implemented, the argument
+ *	passed to @prepare(), @enter() and @finish() is meaningless and should
+ *	be ignored.
  *
- * @finish: Called when the system has left the given state and all devices
- *	are resumed. The return value is ignored.
+ * @prepare: Prepare the platform for entering the system sleep state indicated
+ *	by @set_target() or represented by the argument if @set_target() is not
+ *	implemented.
+ *	@prepare() is called right after devices have been suspended (ie. the
+ *	appropriate .suspend() method has been executed for each device) and
+ *	before the nonboot CPUs are disabled (it is executed with IRQs enabled).
+ *	This callback is optional.  It returns 0 on success or a negative
+ *	error code otherwise, in which case the system cannot enter the desired
+ *	sleep state (@enter() and @finish() will not be called in that case).
+ *
+ * @enter: Enter the system sleep state indicated by @set_target() or
+ *	represented by the argument if @set_target() is not implemented.
+ *	This callback is mandatory.  It returns 0 on success or a negative
+ *	error code otherwise, in which case the system cannot enter the desired
+ *	sleep state.
+ *
+ * @finish: Called when the system has just left a sleep state, right after
+ *	the nonboot CPUs have been enabled and before devices are resumed (it is
+ *	executed with IRQs enabled).  If @set_target() is not implemented, the
+ *	argument represents the sleep state being left.
+ *	This callback is optional, but should be implemented by the platforms
+ *	that implement @prepare().  If implemented, it is always called after
+ *	@enter() (even if @enter() fails).
  */
 struct pm_ops {
 	int (*valid)(suspend_state_t state);
+	int (*set_target)(suspend_state_t state);
 	int (*prepare)(suspend_state_t state);
 	int (*enter)(suspend_state_t state);
 	int (*finish)(suspend_state_t state);
 };
+
+extern struct pm_ops *pm_ops;
 
 /**
  * pm_set_ops - set platform dependent power management ops
  * @pm_ops: The new power management operations to set.
  */
 extern void pm_set_ops(struct pm_ops *pm_ops);
-extern struct pm_ops *pm_ops;
-extern int pm_suspend(suspend_state_t state);
-
 extern int pm_valid_only_mem(suspend_state_t state);
 
 /**
···
  * done. Not called for suspend to disk.
  */
 extern void arch_suspend_enable_irqs(void);
+
+extern int pm_suspend(suspend_state_t state);
 
 /*
  * Device power management

kernel/power/main.c

···
 #include <linux/delay.h>
 #include <linux/errno.h>
 #include <linux/init.h>
-#include <linux/pm.h>
 #include <linux/console.h>
 #include <linux/cpu.h>
 #include <linux/resume-trace.h>
···
 		}
 	}
 
+	if (pm_ops->set_target) {
+		error = pm_ops->set_target(state);
+		if (error)
+			goto Thaw;
+	}
 	suspend_console();
 	error = device_suspend(PMSG_SUSPEND);
 	if (error) {