netvsc: add comments about callback's and NAPI

Add some short description of how callback's and NAPI interoperate.
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc.c

@@ -1209,6 +1209,10 @@ static struct hv_device *netvsc_channel_to_device(struct vmbus_channel *channel)
 	return primary ? primary->device_obj : channel->device_obj;
 }
 
+/* Network processing softirq
+ * Process data in incoming ring buffer from host
+ * Stops when ring is empty or budget is met or exceeded.
+ */
 int netvsc_poll(struct napi_struct *napi, int budget)
 {
 	struct netvsc_channel *nvchan
@@ -1238,7 +1242,11 @@ int netvsc_poll(struct napi_struct *napi, int budget)
 	}
 	hv_pkt_iter_close(channel);
 
-	/* If ring is empty and NAPI is not doing polling */
+	/* If budget was not exhausted and
+	 * not doing busy poll
+	 * then re-enable host interrupts
+	 *  and reschedule if ring is not empty.
+	 */
 	if (work_done < budget &&
 	    napi_complete_done(napi, work_done) &&
 	    hv_end_read(&channel->inbound) != 0)
@@ -1248,6 +1256,9 @@ int netvsc_poll(struct napi_struct *napi, int budget)
 	return work_done;
 }
 
+/* Call back when data is available in host ring buffer.
+ * Processing is deferred until network softirq (NAPI)
+ */
 void netvsc_channel_cb(void *context)
 {
 	struct netvsc_channel *nvchan = context;