[PATCH] PowerMac: force only suspend-to-disk to be valid

For a very long time, echoing 'standby' or 'mem' into /sys/power/state has
killed the machine on powerpc.  This patch fixes that.

This patch adds the .valid callback to pm_ops on PowerMac so that only the
suspend to disk state can be entered.  Note that just returning 0 would
suffice since the upper layers don't pass PM_SUSPEND_DISK down, but we
handle it there regardless just in case that changes.

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/powerpc/platforms/powermac/setup.c

@@ -463,11 +463,23 @@ static int pmac_pm_finish(suspend_state_t state)
 	return 0;
 }
 
+static int pmac_pm_valid(suspend_state_t state)
+{
+	switch (state) {
+	case PM_SUSPEND_DISK:
+		return 1;
+	/* can't do any other states via generic mechanism yet */
+	default:
+		return 0;
+	}
+}
+
 static struct pm_ops pmac_pm_ops = {
 	.pm_disk_mode	= PM_DISK_SHUTDOWN,
 	.prepare	= pmac_pm_prepare,
 	.enter		= pmac_pm_enter,
 	.finish		= pmac_pm_finish,
+	.valid		= pmac_pm_valid,
 };
 
 #endif /* CONFIG_SOFTWARE_SUSPEND */