liquidio: prevent rx queues from getting stalled

This commit has fix for RX traffic issues when we stress test the driver
with continuous ifconfig up/down under very high traffic conditions.

Reason for the issue is that, in existing liquidio_stop function NAPI is
disabled even before actual FW/HW interface is brought down via
send_rx_ctrl_cmd(lio, 0). Between time frame of NAPI disable and actual
interface down in firmware, firmware continuously enqueues rx traffic to
host. When interrupt happens for new packets, host irq handler fails in
scheduling NAPI as the NAPI is already disabled.

After "ifconfig <iface> up", Host re-enables NAPI but cannot schedule it
until it receives another Rx interrupt. Host never receives Rx interrupt as
it never cleared the Rx interrupt it received during interface down
operation. NIC Rx interrupt gets cleared only when Host processes queue and
clears the queue counts. Above anomaly leads to other issues like packet
overflow in FW/HW queues, backpressure.

Fix:
This commit fixes this issue by disabling NAPI only after informing
firmware to stop queueing packets to host via send_rx_ctrl_cmd(lio, 0).
send_rx_ctrl_cmd is not visible in the patch as it is already there in the
code. The DOWN command also waits for any pending packets to be processed
by NAPI so that the deadlock will not occur.

Signed-off-by: Raghu Vatsavayi <[e-mail]>
Acked-by: Derek Chickles <[e-mail]>
Signed-off-by: Felix Manlunas <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/ethernet/cavium/liquidio/lio_core.c

···
 	octeon_free_soft_command(oct, sc);
 	return 0;
 }
+
+int lio_wait_for_clean_oq(struct octeon_device *oct)
+{
+	int retry = 100, pending_pkts = 0;
+	int idx;
+
+	do {
+		pending_pkts = 0;
+
+		for (idx = 0; idx < MAX_OCTEON_OUTPUT_QUEUES(oct); idx++) {
+			if (!(oct->io_qmask.oq & BIT_ULL(idx)))
+				continue;
+			pending_pkts +=
+				atomic_read(&oct->droq[idx]->pkts_pending);
+		}
+
+		if (pending_pkts > 0)
+			schedule_timeout_uninterruptible(1);
+
+	} while (retry-- && pending_pkts);
+
+	return pending_pkts;
+}

drivers/net/ethernet/cavium/liquidio/lio_main.c

···
 	struct octeon_device *oct = lio->oct_dev;
 	struct napi_struct *napi, *n;
 
-	if (oct->props[lio->ifidx].napi_enabled) {
-		list_for_each_entry_safe(napi, n, &netdev->napi_list, dev_list)
-			napi_disable(napi);
-
-		oct->props[lio->ifidx].napi_enabled = 0;
-
-		if (OCTEON_CN23XX_PF(oct))
-			oct->droq[0]->ops.poll_mode = 0;
-	}
-
 	ifstate_reset(lio, LIO_IFSTATE_RUNNING);
 
 	netif_tx_disable(netdev);
···
 	if (lio->ptp_clock) {
 		ptp_clock_unregister(lio->ptp_clock);
 		lio->ptp_clock = NULL;
+	}
+
+	/* Wait for any pending Rx descriptors */
+	if (lio_wait_for_clean_oq(oct))
+		netif_info(lio, rx_err, lio->netdev,
+			   "Proceeding with stop interface after partial RX desc processing\n");
+
+	if (oct->props[lio->ifidx].napi_enabled == 1) {
+		list_for_each_entry_safe(napi, n, &netdev->napi_list, dev_list)
+			napi_disable(napi);
+
+		oct->props[lio->ifidx].napi_enabled = 0;
+
+		if (OCTEON_CN23XX_PF(oct))
+			oct->droq[0]->ops.poll_mode = 0;
 	}
 
 	dev_info(&oct->pci_dev->dev, "%s interface is stopped\n", netdev->name);

drivers/net/ethernet/cavium/liquidio/lio_vf_main.c

···
 	/* tell Octeon to stop forwarding packets to host */
 	send_rx_ctrl_cmd(lio, 0);
 
-	if (oct->props[lio->ifidx].napi_enabled) {
-		list_for_each_entry_safe(napi, n, &netdev->napi_list, dev_list)
-			napi_disable(napi);
-
-		oct->props[lio->ifidx].napi_enabled = 0;
-
-		oct->droq[0]->ops.poll_mode = 0;
-	}
-
 	netif_info(lio, ifdown, lio->netdev, "Stopping interface!\n");
 	/* Inform that netif carrier is down */
 	lio->intf_open = 0;
···
 	ifstate_reset(lio, LIO_IFSTATE_RUNNING);
 
 	stop_txqs(netdev);
+
+	/* Wait for any pending Rx descriptors */
+	if (lio_wait_for_clean_oq(oct))
+		netif_info(lio, rx_err, lio->netdev,
+			   "Proceeding with stop interface after partial RX desc processing\n");
+
+	if (oct->props[lio->ifidx].napi_enabled == 1) {
+		list_for_each_entry_safe(napi, n, &netdev->napi_list, dev_list)
+			napi_disable(napi);
+
+		oct->props[lio->ifidx].napi_enabled = 0;
+
+		oct->droq[0]->ops.poll_mode = 0;
+	}
 
 	dev_info(&oct->pci_dev->dev, "%s interface is stopped\n", netdev->name);
 

drivers/net/ethernet/cavium/liquidio/octeon_network.h

···
 
 int octeon_setup_interrupt(struct octeon_device *oct, u32 num_ioqs);
 
+int lio_wait_for_clean_oq(struct octeon_device *oct);
 /**
  * \brief Register ethtool operations
  * @param netdev    pointer to network device