net/enetc: do not stall in clean Tx ring

[dpdk.git] / drivers / net / enetc / enetc_rxtx.c

diff --git a/drivers/net/enetc/enetc_rxtx.c b/drivers/net/enetc/enetc_rxtx.c
index 81b0ef3..b7ecb75 100644 (file)
--- a/drivers/net/enetc/enetc_rxtx.c
+++ b/drivers/net/enetc/enetc_rxtx.c
@@ -1,5 +1,5 @@
 /* SPDX-License-Identifier: BSD-3-Clause
- * Copyright 2018-2019 NXP
+ * Copyright 2018-2020 NXP
  */
 
 #include <stdbool.h>
@@ -21,12 +21,24 @@ enetc_clean_tx_ring(struct enetc_bdr *tx_ring)
 {
        int tx_frm_cnt = 0;
        struct enetc_swbd *tx_swbd;
-       int i;
+       int i, hwci;
 
        i = tx_ring->next_to_clean;
        tx_swbd = &tx_ring->q_swbd[i];
-       while ((int)(enetc_rd_reg(tx_ring->tcisr) &
-              ENETC_TBCISR_IDX_MASK) != i) {
+
+       hwci = (int)(enetc_rd_reg(tx_ring->tcisr) &
+                    ENETC_TBCISR_IDX_MASK);
+
+       /* we're only reading the CI index once here, which means HW may update
+        * it while we're doing clean-up.  We could read the register in a loop
+        * but for now I assume it's OK to leave a few Tx frames for next call.
+        * The issue with reading the register in a loop is that we're stalling
+        * here trying to catch up with HW which keeps sending traffic as long
+        * as it has traffic to send, so in effect we could be waiting here for
+        * the Tx ring to be drained by HW, instead of us doing Rx in that
+        * meantime.
+        */
+       while (i != hwci) {
                rte_pktmbuf_free(tx_swbd->buffer_addr);
                tx_swbd->buffer_addr = NULL;
                tx_swbd++;