sunvnet: Return from vnet_napi_event() if no packets to read

vnet_event_napi() may be called as part of the NAPI ->poll,
to resume reading descriptor rings. When no data is available,
descriptor ring state (e.g., rcv_nxt) needs to be reset
carefully to stay in lock-step with ldc_read(). In the interest
of simplicity, the best way to do this is to return from
vnet_event_napi() when there are no more packets to read.
The next trip through ldc_rx will correctly set up the dring state.
Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Tested-by: David Stevens <david.stevens@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/sun/sunvnet.c

@@ -691,7 +691,6 @@ static int vnet_event_napi(struct vnet_port *port, int budget)
 			pkt->end_idx = -1;
 			goto napi_resume;
 		}
-ldc_read:
 		err = ldc_read(vio->lp, &msgbuf, sizeof(msgbuf));
 		if (unlikely(err < 0)) {
 			if (err == -ECONNRESET)
@@ -722,8 +721,8 @@ static int vnet_event_napi(struct vnet_port *port, int budget)
 				err = vnet_rx(port, &msgbuf, &npkts, budget);
 				if (npkts >= budget)
 					break;
-				if (npkts == 0 && err != -ECONNRESET)
-					goto ldc_read;
+				if (npkts == 0)
+					break;
 			} else if (msgbuf.tag.stype == VIO_SUBTYPE_ACK) {
 				err = vnet_ack(port, &msgbuf);
 				if (err > 0)