drm/nouveau/perfmon: use private spinlock to control exclusive access to perfmon

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/engine/pm.h

@@ -7,7 +7,10 @@ struct nvkm_pm {
 	const struct nvkm_pm_func *func;
 	struct nvkm_engine engine;
 
-	struct nvkm_object *perfmon;
+	struct {
+		spinlock_t lock;
+		struct nvkm_object *object;
+	} client;
 
 	struct list_head domains;
 	struct list_head sources;

drivers/gpu/drm/nouveau/nvkm/engine/pm/base.c

@@ -628,10 +628,10 @@ nvkm_perfmon_dtor(struct nvkm_object *object)
 {
 	struct nvkm_perfmon *perfmon = nvkm_perfmon(object);
 	struct nvkm_pm *pm = perfmon->pm;
-	mutex_lock(&pm->engine.subdev.mutex);
-	if (pm->perfmon == &perfmon->object)
-		pm->perfmon = NULL;
-	mutex_unlock(&pm->engine.subdev.mutex);
+	spin_lock(&pm->client.lock);
+	if (pm->client.object == &perfmon->object)
+		pm->client.object = NULL;
+	spin_unlock(&pm->client.lock);
 	return perfmon;
 }
 
@@ -671,11 +671,11 @@ nvkm_pm_oclass_new(struct nvkm_device *device, const struct nvkm_oclass *oclass,
 	if (ret)
 		return ret;
 
-	mutex_lock(&pm->engine.subdev.mutex);
-	if (pm->perfmon == NULL)
-		pm->perfmon = *pobject;
-	ret = (pm->perfmon == *pobject) ? 0 : -EBUSY;
-	mutex_unlock(&pm->engine.subdev.mutex);
+	spin_lock(&pm->client.lock);
+	if (pm->client.object == NULL)
+		pm->client.object = *pobject;
+	ret = (pm->client.object == *pobject) ? 0 : -EBUSY;
+	spin_unlock(&pm->client.lock);
 	return ret;
 }
 
@@ -863,5 +863,6 @@ nvkm_pm_ctor(const struct nvkm_pm_func *func, struct nvkm_device *device,
 	pm->func = func;
 	INIT_LIST_HEAD(&pm->domains);
 	INIT_LIST_HEAD(&pm->sources);
+	spin_lock_init(&pm->client.lock);
 	return nvkm_engine_ctor(&nvkm_pm, device, index, true, &pm->engine);
 }