drm/nouveau: use the new interator in nv50_wndw_prepare_fb

Makes the handling a bit more complex, but avoids the use of
dma_resv_get_excl_unlocked().
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20211005113742.1101-27-christian.koenig@amd.com

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

@@ -539,6 +539,8 @@ 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);
@@ -561,7 +563,13 @@ nv50_wndw_prepare_fb(struct drm_plane *plane, struct drm_plane_state *state)
 			asyw->image.handle[0] = ctxdma->object.handle;
 	}
 
-	asyw->state.fence = dma_resv_get_excl_unlocked(nvbo->bo.base.resv);
+	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);
 	asyw->image.offset[0] = nvbo->offset;
 
 	if (wndw->func->prepare) {