drm/nouveau/mmu: automatically handle "un-bootstrapping" of vmm

Removes the need to expose internals outside of MMU, and GP100 is both
different, and a lot harder to deal with.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/include/nvkm/subdev/mmu.h

@@ -38,6 +38,8 @@ struct nvkm_vm {
 	struct nvkm_vm_pgt *pgt;
 	u32 fpde;
 	u32 lpde;
+
+	bool bootstrapped;
 };
 
 int  nvkm_vm_new(struct nvkm_device *, u64 offset, u64 length, u64 mm_offset,

drivers/gpu/drm/nouveau/nvkm/subdev/bar/gf100.c

@@ -168,10 +168,7 @@ gf100_bar_dtor(struct nvkm_bar *base)
 	nvkm_gpuobj_del(&bar->bar[1].pgd);
 	nvkm_memory_unref(&bar->bar[1].mem);
 
-	if (bar->bar[0].vm) {
-		nvkm_memory_unref(&bar->bar[0].vm->pgt[0].mem[0]);
 	nvkm_vm_ref(NULL, &bar->bar[0].vm, bar->bar[0].pgd);
-	}
 	nvkm_gpuobj_del(&bar->bar[0].pgd);
 	nvkm_memory_unref(&bar->bar[0].mem);
 	return bar;

drivers/gpu/drm/nouveau/nvkm/subdev/bar/nv50.c

@@ -200,10 +200,7 @@ nv50_bar_dtor(struct nvkm_bar *base)
 	nvkm_gpuobj_del(&bar->bar1);
 	nvkm_vm_ref(NULL, &bar->bar1_vm, bar->pgd);
 	nvkm_gpuobj_del(&bar->bar2);
-	if (bar->bar2_vm) {
-		nvkm_memory_unref(&bar->bar2_vm->pgt[0].mem[0]);
 	nvkm_vm_ref(NULL, &bar->bar2_vm, bar->pgd);
-	}
 	nvkm_gpuobj_del(&bar->pgd);
 	nvkm_gpuobj_del(&bar->pad);
 	nvkm_gpuobj_del(&bar->mem);

drivers/gpu/drm/nouveau/nvkm/subdev/mmu/base.c

@@ -357,6 +357,7 @@ nvkm_vm_boot(struct nvkm_vm *vm, u64 size)
 		vm->pgt[0].refcount[0] = 1;
 		vm->pgt[0].mem[0] = pgt;
 		nvkm_memory_boot(pgt, vm);
+		vm->bootstrapped = true;
 	}
 
 	return ret;
@@ -481,6 +482,8 @@ nvkm_vm_ref(struct nvkm_vm *ref, struct nvkm_vm **ptr, struct nvkm_gpuobj *pgd)
 	}
 
 	if (*ptr) {
+		if ((*ptr)->bootstrapped && pgd)
+			nvkm_memory_unref(&(*ptr)->pgt[0].mem[0]);
 		nvkm_vm_unlink(*ptr, pgd);
 		kref_put(&(*ptr)->refcount, nvkm_vm_del);
 	}