vmbus: add direct isr callback mode

Change the simple boolean batched_reading into a tri-value.
For future NAPI support in netvsc driver, the callback needs to
occur directly in interrupt handler.

Batched mode is also changed to disable host interrupts immediately
in interrupt routine (to avoid unnecessary host signals), and the
tasklet is rescheduled if more data is detected.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/vmbus_drv.c

@@ -886,6 +886,18 @@ msg_handled:
 }
 
 
+/*
+ * Direct callback for channels using other deferred processing
+ */
+static void vmbus_channel_isr(struct vmbus_channel *channel)
+{
+	void (*callback_fn)(void *);
+
+	callback_fn = READ_ONCE(channel->onchannel_callback);
+	if (likely(callback_fn != NULL))
+		(*callback_fn)(channel->channel_callback_context);
+}
+
 /*
  * Schedule all channels with events pending
  */
@@ -927,9 +939,19 @@ static void vmbus_chan_sched(struct hv_per_cpu_context *hv_cpu)
 
 		/* Find channel based on relid */
 		list_for_each_entry(channel, &hv_cpu->chan_list, percpu_list) {
-			if (channel->offermsg.child_relid == relid) {
-				tasklet_schedule(&channel->callback_event);
+			if (channel->offermsg.child_relid != relid)
+				continue;
+
+			switch (channel->callback_mode) {
+			case HV_CALL_ISR:
+				vmbus_channel_isr(channel);
 				break;
+
+			case HV_CALL_BATCHED:
+				hv_begin_read(&channel->inbound);
+				/* fallthrough */
+			case HV_CALL_DIRECT:
+				tasklet_schedule(&channel->callback_event);
 			}
 		}
 	}