nouveau: rip out fence irq allow/block sequences.

fences are signalled on nvidia hw using non-stall interrupts.

non-stall interrupts are not latched from my reading.

When nouveau emits a fence, it requests a NON_STALL signalling,
but it only calls the interface to allow the non-stall irq to happen
after it has already emitted the fence. A recent change
eacabb5 ("nouveau: push event block/allowing out of the fence context")
made this worse by pushing out the fence allow/block to a workqueue.

However I can't see how this could ever work great, since when
enable signalling is called, the semaphore has already been emitted
to the ring, and the hw could already have tried to set the bits,
but it's been masked off. Changing the allowed mask later won't make
the interrupt get called again.

For now rip all of this out.

This fixes a bunch of stalls seen running VK CTS sync tests.

Signed-off-by: Dave Airlie <airlied@redhat.com>

Author: airlied

drivers/gpu/drm/nouveau/nouveau_fence.c

@@ -50,24 +50,14 @@ nouveau_fctx(struct nouveau_fence *fence)
 	return container_of(fence->base.lock, struct nouveau_fence_chan, lock);
 }
 
-static int
+static void
 nouveau_fence_signal(struct nouveau_fence *fence)
 {
-	int drop = 0;
-
 	dma_fence_signal_locked(&fence->base);
 	list_del(&fence->head);
 	rcu_assign_pointer(fence->channel, NULL);
 
-	if (test_bit(DMA_FENCE_FLAG_USER_BITS, &fence->base.flags)) {
-		struct nouveau_fence_chan *fctx = nouveau_fctx(fence);
-
-		if (atomic_dec_and_test(&fctx->notify_ref))
-			drop = 1;
-	}
-
 	dma_fence_put(&fence->base);
-	return drop;
 }
 
 static struct nouveau_fence *
@@ -93,8 +83,7 @@ nouveau_fence_context_kill(struct nouveau_fence_chan *fctx, int error)
 		if (error)
 			dma_fence_set_error(&fence->base, error);
 
-		if (nouveau_fence_signal(fence))
-			nvif_event_block(&fctx->event);
+		nouveau_fence_signal(fence);
 	}
 	fctx->killed = 1;
 	spin_unlock_irqrestore(&fctx->lock, flags);
@@ -103,8 +92,8 @@ nouveau_fence_context_kill(struct nouveau_fence_chan *fctx, int error)
 void
 nouveau_fence_context_del(struct nouveau_fence_chan *fctx)
 {
-	cancel_work_sync(&fctx->allow_block_work);
 	nouveau_fence_context_kill(fctx, 0);
+	nvif_event_block(&fctx->event);
 	nvif_event_dtor(&fctx->event);
 	fctx->dead = 1;
 
@@ -127,11 +116,10 @@ nouveau_fence_context_free(struct nouveau_fence_chan *fctx)
 	kref_put(&fctx->fence_ref, nouveau_fence_context_put);
 }
 
-static int
+static void
 nouveau_fence_update(struct nouveau_channel *chan, struct nouveau_fence_chan *fctx)
 {
 	struct nouveau_fence *fence;
-	int drop = 0;
 	u32 seq = fctx->read(chan);
 
 	while (!list_empty(&fctx->pending)) {
@@ -140,10 +128,8 @@ nouveau_fence_update(struct nouveau_channel *chan, struct nouveau_fence_chan *fc
 		if ((int)(seq - fence->base.seqno) < 0)
 			break;
 
-		drop |= nouveau_fence_signal(fence);
+		nouveau_fence_signal(fence);
 	}
-
-	return drop;
 }
 
 static int
@@ -160,26 +146,13 @@ nouveau_fence_wait_uevent_handler(struct nvif_event *event, void *repv, u32 repc
 
 		fence = list_entry(fctx->pending.next, typeof(*fence), head);
 		chan = rcu_dereference_protected(fence->channel, lockdep_is_held(&fctx->lock));
-		if (nouveau_fence_update(chan, fctx))
-			ret = NVIF_EVENT_DROP;
+		nouveau_fence_update(chan, fctx);
 	}
 	spin_unlock_irqrestore(&fctx->lock, flags);
 
 	return ret;
 }
 
-static void
-nouveau_fence_work_allow_block(struct work_struct *work)
-{
-	struct nouveau_fence_chan *fctx = container_of(work, struct nouveau_fence_chan,
-						       allow_block_work);
-
-	if (atomic_read(&fctx->notify_ref) == 0)
-		nvif_event_block(&fctx->event);
-	else
-		nvif_event_allow(&fctx->event);
-}
-
 void
 nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_chan *fctx)
 {
@@ -191,7 +164,6 @@ nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_cha
 	} args;
 	int ret;
 
-	INIT_WORK(&fctx->allow_block_work, nouveau_fence_work_allow_block);
 	INIT_LIST_HEAD(&fctx->flip);
 	INIT_LIST_HEAD(&fctx->pending);
 	spin_lock_init(&fctx->lock);
@@ -216,6 +188,12 @@ nouveau_fence_context_new(struct nouveau_channel *chan, struct nouveau_fence_cha
 			      &args.base, sizeof(args), &fctx->event);
 
 	WARN_ON(ret);
+
+	/*
+	 * Always allow non-stall irq events - previously this code tried to
+	 * enable/disable them, but that just seems racy as nonstall irqs are unlatched.
+	 */
+	nvif_event_allow(&fctx->event);
 }
 
 int
@@ -247,8 +225,7 @@ nouveau_fence_emit(struct nouveau_fence *fence)
 			return -ENODEV;
 		}
 
-		if (nouveau_fence_update(chan, fctx))
-			nvif_event_block(&fctx->event);
+		nouveau_fence_update(chan, fctx);
 
 		list_add_tail(&fence->head, &fctx->pending);
 		spin_unlock_irq(&fctx->lock);
@@ -271,8 +248,8 @@ nouveau_fence_done(struct nouveau_fence *fence)
 
 		spin_lock_irqsave(&fctx->lock, flags);
 		chan = rcu_dereference_protected(fence->channel, lockdep_is_held(&fctx->lock));
-		if (chan && nouveau_fence_update(chan, fctx))
-			nvif_event_block(&fctx->event);
+		if (chan)
+			nouveau_fence_update(chan, fctx);
 		spin_unlock_irqrestore(&fctx->lock, flags);
 	}
 	return dma_fence_is_signaled(&fence->base);
@@ -530,32 +507,10 @@ static const struct dma_fence_ops nouveau_fence_ops_legacy = {
 	.release = nouveau_fence_release
 };
 
-static bool nouveau_fence_enable_signaling(struct dma_fence *f)
-{
-	struct nouveau_fence *fence = from_fence(f);
-	struct nouveau_fence_chan *fctx = nouveau_fctx(fence);
-	bool ret;
-	bool do_work;
-
-	if (atomic_inc_return(&fctx->notify_ref) == 0)
-		do_work = true;
-
-	ret = nouveau_fence_no_signaling(f);
-	if (ret)
-		set_bit(DMA_FENCE_FLAG_USER_BITS, &fence->base.flags);
-	else if (atomic_dec_and_test(&fctx->notify_ref))
-		do_work = true;
-
-	if (do_work)
-		schedule_work(&fctx->allow_block_work);
-
-	return ret;
-}
-
 static const struct dma_fence_ops nouveau_fence_ops_uevent = {
 	.get_driver_name = nouveau_fence_get_get_driver_name,
 	.get_timeline_name = nouveau_fence_get_timeline_name,
-	.enable_signaling = nouveau_fence_enable_signaling,
+	.enable_signaling = nouveau_fence_no_signaling,
 	.signaled = nouveau_fence_is_signaled,
 	.release = nouveau_fence_release
 };

drivers/gpu/drm/nouveau/nouveau_fence.h

@@ -46,8 +46,6 @@ struct nouveau_fence_chan {
 	char name[32];
 
 	struct nvif_event event;
-	struct work_struct allow_block_work;
-	atomic_t notify_ref;
 	int dead, killed;
 };