drm/nouveau: support synchronous pushbuf submission

This is useful for debugging GPU hangs.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_gem.c

@@ -688,7 +688,7 @@ nouveau_gem_ioctl_pushbuf(struct drm_device *dev, void *data,
 	struct validate_op op;
 	struct nouveau_fence *fence = NULL;
 	int i, j, ret = 0;
-	bool do_reloc = false;
+	bool do_reloc = false, sync = false;
 
 	if (unlikely(!abi16))
 		return -ENOMEM;
@@ -705,6 +705,8 @@ nouveau_gem_ioctl_pushbuf(struct drm_device *dev, void *data,
 	if (unlikely(atomic_read(&chan->killed)))
 		return nouveau_abi16_put(abi16, -ENODEV);
 
+	sync = req->vram_available & NOUVEAU_GEM_PUSHBUF_SYNC;
+
 	req->vram_available = drm->gem.vram_available;
 	req->gart_available = drm->gem.gart_available;
 	if (unlikely(req->nr_push == 0))
@@ -852,6 +854,13 @@ nouveau_gem_ioctl_pushbuf(struct drm_device *dev, void *data,
 		goto out;
 	}
 
+	if (sync) {
+		if (!(ret = nouveau_fence_wait(fence, false, false))) {
+			if ((ret = dma_fence_get_status(&fence->base)) == 1)
+				ret = 0;
+		}
+	}
+
 out:
 	validate_fini(&op, chan, fence, bo);
 	nouveau_fence_unref(&fence);

include/uapi/drm/nouveau_drm.h

@@ -110,6 +110,7 @@ struct drm_nouveau_gem_pushbuf {
 	__u64 push;
 	__u32 suffix0;
 	__u32 suffix1;
+#define NOUVEAU_GEM_PUSHBUF_SYNC                                    (1ULL << 0)
 	__u64 vram_available;
 	__u64 gart_available;
 };