On Tue,  8 Dec 2020 16:54:44 -0800 Wei Wang wrote:

+static void dev_disable_threaded_all(struct net_device *dev)
+{
+	struct napi_struct *napi;
+
+	list_for_each_entry(napi, &dev->napi_list, dev_list)
+		napi_set_threaded(napi, false);
+}

This is an implementation detail which should be hidden in dev.c IMHO.
Since the sysfs knob is just a device global on/off the iteration over
napis and all is best hidden away.

(sorry about the delayed review BTW, hope we can do a minor revision
and still hit 5.12)

+static int modify_napi_threaded(struct net_device *dev, unsigned long val)
+{
+	struct napi_struct *napi;
+	int ret;
+
+	if (list_empty(&dev->napi_list))
+		return -EOPNOTSUPP;
+
+	list_for_each_entry(napi, &dev->napi_list, dev_list) {
+		ret = napi_set_threaded(napi, !!val);
+		if (ret) {
+			/* Error occurred on one of the napi,
+			 * reset threaded mode on all napi.
+			 */
+			dev_disable_threaded_all(dev);
+			break;
+		}
+	}
+
+	return ret;
+}