drm/nouveau/fb: protect vram mm with private mutex

nvkm_subdev.mutex is going away.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>

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

@@ -132,6 +132,7 @@ struct nvkm_ram {
 #define NVKM_RAM_MM_MIXED  (NVKM_MM_HEAP_ANY + 3)
 	struct nvkm_mm vram;
 	u64 stolen;
+	struct mutex mutex;
 
 	int ranks;
 	int parts;

drivers/gpu/drm/nouveau/nvkm/subdev/fb/ram.c

@@ -81,12 +81,12 @@ nvkm_vram_dtor(struct nvkm_memory *memory)
 	struct nvkm_vram *vram = nvkm_vram(memory);
 	struct nvkm_mm_node *next = vram->mn;
 	struct nvkm_mm_node *node;
-	mutex_lock(&vram->ram->fb->subdev.mutex);
+	mutex_lock(&vram->ram->mutex);
 	while ((node = next)) {
 		next = node->next;
 		nvkm_mm_free(&vram->ram->vram, &node);
 	}
-	mutex_unlock(&vram->ram->fb->subdev.mutex);
+	mutex_unlock(&vram->ram->mutex);
 	return vram;
 }
 
@@ -126,7 +126,7 @@ nvkm_ram_get(struct nvkm_device *device, u8 heap, u8 type, u8 rpage, u64 size,
 	vram->page = page;
 	*pmemory = &vram->memory;
 
-	mutex_lock(&ram->fb->subdev.mutex);
+	mutex_lock(&ram->mutex);
 	node = &vram->mn;
 	do {
 		if (back)
@@ -134,7 +134,7 @@ nvkm_ram_get(struct nvkm_device *device, u8 heap, u8 type, u8 rpage, u64 size,
 		else
 			ret = nvkm_mm_head(mm, heap, type, max, min, align, &r);
 		if (ret) {
-			mutex_unlock(&ram->fb->subdev.mutex);
+			mutex_unlock(&ram->mutex);
 			nvkm_memory_unref(pmemory);
 			return ret;
 		}
@@ -143,7 +143,7 @@ nvkm_ram_get(struct nvkm_device *device, u8 heap, u8 type, u8 rpage, u64 size,
 		node = &r->next;
 		max -= r->length;
 	} while (max);
-	mutex_unlock(&ram->fb->subdev.mutex);
+	mutex_unlock(&ram->mutex);
 	return 0;
 }
 
@@ -163,6 +163,7 @@ nvkm_ram_del(struct nvkm_ram **pram)
 		if (ram->func->dtor)
 			*pram = ram->func->dtor(ram);
 		nvkm_mm_fini(&ram->vram);
+		mutex_destroy(&ram->mutex);
 		kfree(*pram);
 		*pram = NULL;
 	}
@@ -196,6 +197,7 @@ nvkm_ram_ctor(const struct nvkm_ram_func *func, struct nvkm_fb *fb,
 	ram->fb = fb;
 	ram->type = type;
 	ram->size = size;
+	mutex_init(&ram->mutex);
 
 	if (!nvkm_mm_initialised(&ram->vram)) {
 		ret = nvkm_mm_init(&ram->vram, NVKM_RAM_MM_NORMAL, 0,