powerpc/ps3: Convert half completion to rcuwait

The PS3 notification interrupt and kthread use a hacked up completion to
communicate. Since we're wanting to change the completion implementation and
this is abuse anyway, replace it with a simple rcuwait since there is only ever
the one waiter.

AFAICT the kthread uses TASK_INTERRUPTIBLE to not increase loadavg, kthreads
cannot receive signals by default and this one doesn't look different. Use
TASK_IDLE instead.

Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Peter Zijlstra (Intel) <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/powerpc/platforms/ps3/device-init.c

···
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/reboot.h>
+#include <linux/rcuwait.h>
 
 #include <asm/firmware.h>
 #include <asm/lv1call.h>
···
 	spinlock_t lock;
 	u64 tag;
 	u64 lv1_status;
-	struct completion done;
+	struct rcuwait wait;
+	bool done;
 };
 
 enum ps3_notify_type {
···
 		pr_debug("%s:%u: completed, status 0x%llx\n", __func__,
 			 __LINE__, status);
 		dev->lv1_status = status;
-		complete(&dev->done);
+		dev->done = true;
+		rcuwait_wake_up(&dev->wait);
 	}
 	spin_unlock(&dev->lock);
 	return IRQ_HANDLED;
···
 	unsigned long flags;
 	int res;
 
-	init_completion(&dev->done);
 	spin_lock_irqsave(&dev->lock, flags);
 	res = write ? lv1_storage_write(dev->sbd.dev_id, 0, 0, 1, 0, lpar,
 					&dev->tag)
 		    : lv1_storage_read(dev->sbd.dev_id, 0, 0, 1, 0, lpar,
 				       &dev->tag);
+	dev->done = false;
 	spin_unlock_irqrestore(&dev->lock, flags);
 	if (res) {
 		pr_err("%s:%u: %s failed %d\n", __func__, __LINE__, op, res);
···
 	}
 	pr_debug("%s:%u: notification %s issued\n", __func__, __LINE__, op);
 
-	res = wait_event_interruptible(dev->done.wait,
-				       dev->done.done || kthread_should_stop());
+	rcuwait_wait_event(&dev->wait, dev->done || kthread_should_stop(), TASK_IDLE);
+
 	if (kthread_should_stop())
 		res = -EINTR;
-	if (res) {
-		pr_debug("%s:%u: interrupted %s\n", __func__, __LINE__, op);
-		return res;
-	}
 
 	if (dev->lv1_status) {
 		pr_err("%s:%u: %s not completed, status 0x%llx\n", __func__,
···
 	}
 
 	spin_lock_init(&dev.lock);
+	rcuwait_init(&dev.wait);
 
 	res = request_irq(irq, ps3_notification_interrupt, 0,
 			  "ps3_notification", &dev);