power management: force pm_ops.valid callback to be assigned

This patch changes the docs and behaviour from "all states valid" to "no
states valid" if no .valid callback is assigned.  Users of pm_ops that only
need mem sleep can assign pm_valid_only_mem without any overhead, others
will require more elaborate callbacks.

Now that all users of pm_ops have a .valid callback this is a safe thing to
do and prevents things from getting messy again as they were before.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Pavel Machek <pavel@ucw.cz>
Looks-okay-to: Rafael J. Wysocki <rjw@sisk.pl>
Cc: <linux-pm@lists.linux-foundation.org>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/pm.h

@@ -125,12 +125,12 @@ typedef int __bitwise suspend_disk_method_t;
  * struct pm_ops - Callbacks for managing platform dependent suspend states.
  * @valid: Callback to determine whether the given state can be entered.
  * 	If %CONFIG_SOFTWARE_SUSPEND is set then %PM_SUSPEND_DISK is
- *	always valid and never passed to this call.
- *	If not assigned, all suspend states are advertised as valid
- *	in /sys/power/state (but can still be rejected by prepare or enter.)
- *	Since new states can be added for other platforms, you should
- *	assign this callback. There is a %pm_valid_only_mem function
- *	available if you only implemented mem sleep.
+ *	always valid and never passed to this call. If not assigned,
+ *	no suspend states are valid.
+ *	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.
  *
  * @prepare: Prepare the platform for the given suspend state. Can return a
  *	negative error code if necessary.

kernel/power/main.c

@@ -198,8 +198,8 @@ static inline int valid_state(suspend_state_t state)
 
 	/* all other states need lowlevel support and need to be
 	 * valid to the lowlevel implementation, no valid callback
-	 * implies that all are valid. */
-	if (!pm_ops || (pm_ops->valid && !pm_ops->valid(state)))
+	 * implies that none are valid. */
+	if (!pm_ops || !pm_ops->valid || !pm_ops->valid(state))
 		return 0;
 	return 1;
 }