drm/nouveau: support more than one write fence in fenv50_wndw_prepare_fb

Use dma_resv_get_singleton() here to eventually get more than one write
fence as single fence.
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Lyude Paul <lyude@redhat.com>
Cc: nouveau@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20220321135856.1331-14-christian.koenig@amd.com

drivers/gpu/drm/nouveau/dispnv50/wndw.c

@@ -536,8 +536,6 @@ nv50_wndw_prepare_fb(struct drm_plane *plane, struct drm_plane_state *state)
 	struct nouveau_bo *nvbo;
 	struct nv50_head_atom *asyh;
 	struct nv50_wndw_ctxdma *ctxdma;
-	struct dma_resv_iter cursor;
-	struct dma_fence *fence;
 	int ret;
 
 	NV_ATOMIC(drm, "%s prepare: %p\n", plane->name, fb);
@@ -560,13 +558,11 @@ nv50_wndw_prepare_fb(struct drm_plane *plane, struct drm_plane_state *state)
 			asyw->image.handle[0] = ctxdma->object.handle;
 	}
 
-	dma_resv_iter_begin(&cursor, nvbo->bo.base.resv, false);
-	dma_resv_for_each_fence_unlocked(&cursor, fence) {
-		/* TODO: We only use the first writer here */
-		asyw->state.fence = dma_fence_get(fence);
-		break;
-	}
-	dma_resv_iter_end(&cursor);
+	ret = dma_resv_get_singleton(nvbo->bo.base.resv, false,
+				     &asyw->state.fence);
+	if (ret)
+		return ret;
+
 	asyw->image.offset[0] = nvbo->offset;
 
 	if (wndw->func->prepare) {