drm/nouveau/kms/nv50-: fix case where notifier buffer is at offset 0

VRAM offset 0 is a valid address, triggered on GA102.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

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

@@ -222,7 +222,7 @@ nv50_dmac_wait(struct nvif_push *push, u32 size)
 
 int
 nv50_dmac_create(struct nvif_device *device, struct nvif_object *disp,
-		 const s32 *oclass, u8 head, void *data, u32 size, u64 syncbuf,
+		 const s32 *oclass, u8 head, void *data, u32 size, s64 syncbuf,
 		 struct nv50_dmac *dmac)
 {
 	struct nouveau_cli *cli = (void *)device->object.client;
@@ -271,7 +271,7 @@ nv50_dmac_create(struct nvif_device *device, struct nvif_object *disp,
 	if (ret)
 		return ret;
 
-	if (!syncbuf)
+	if (syncbuf < 0)
 		return 0;
 
 	ret = nvif_object_ctor(&dmac->base.user, "kmsSyncCtxDma", NV50_DISP_HANDLE_SYNCBUF,

drivers/gpu/drm/nouveau/dispnv50/disp.h

@@ -95,7 +95,7 @@ struct nv50_outp_atom {
 
 int nv50_dmac_create(struct nvif_device *device, struct nvif_object *disp,
 		     const s32 *oclass, u8 head, void *data, u32 size,
-		     u64 syncbuf, struct nv50_dmac *dmac);
+		     s64 syncbuf, struct nv50_dmac *dmac);
 void nv50_dmac_destroy(struct nv50_dmac *);
 
 /*

drivers/gpu/drm/nouveau/dispnv50/wimmc37b.c

@@ -76,7 +76,7 @@ wimmc37b_init_(const struct nv50_wimm_func *func, struct nouveau_drm *drm,
 	int ret;
 
 	ret = nv50_dmac_create(&drm->client.device, &disp->disp->object,
-			       &oclass, 0, &args, sizeof(args), 0,
+			       &oclass, 0, &args, sizeof(args), -1,
 			       &wndw->wimm);
 	if (ret) {
 		NV_ERROR(drm, "wimm%04x allocation failed: %d\n", oclass, ret);