[dpdk-dev] [RFC] app/testpmd: fix MTU after device configure

[Ferruh Yigit]

In 'rte_eth_dev_configure()', if 'DEV_RX_OFFLOAD_JUMBO_FRAME' is not set
the max frame size is limited to 'RTE_ETHER_MAX_LEN' (1518).
This is mistake because for the PMDs that has frame size bigger than
"RTE_ETHER_HDR_LEN + RTE_ETHER_CRC_LEN" (18 bytes), the MTU becomes
less than 1500, causing a valid frame with 1500 bytes payload to be
dropped.

Since 'rte_eth_dev_set_mtu()' works as expected, it is called after
'rte_eth_dev_configure()' to fix the MTU.
It may look redundant to set MTU after 'rte_eth_dev_configure()', both
with default values, but it is not, the resulting MTU config can be
different in the device based on frame overhead of the PMD.

And instead of setting the MTU to default value, it is first get via
'rte_eth_dev_get_mtu()' and set again, this is to cover cases MTU
changed from testpmd command line.

'rte_eth_dev_set_mtu()', '-ENOTSUP' error is ignored to prevent
irrelevant warning messages for the virtual PMDs.

Signed-off-by: Ferruh Yigit <ferruh.yigit at intel.com>
---
Cc: Steve Yang <stevex.yang at intel.com>
Cc: Thomas Monjalon <thomas at monjalon.net>
Cc: Andrew Rybchenko <andrew.rybchenko at oktetlabs.ru>
Cc: Konstantin Ananyev <konstantin.ananyev at intel.com>
Cc: Olivier Matz <olivier.matz at 6wind.com>
Cc: Lance Richardson <lance.richardson at broadcom.com>
---
 app/test-pmd/testpmd.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
index 33fc0fddf5..48e9647fc7 100644
--- a/app/test-pmd/testpmd.c
+++ b/app/test-pmd/testpmd.c
@@ -2537,6 +2537,8 @@ start_port(portid_t pid)
 		}
 
 		if (port->need_reconfig > 0) {
+			uint16_t mtu = RTE_ETHER_MTU;
+
 			port->need_reconfig = 0;
 
 			if (flow_isolate_all) {
@@ -2570,6 +2572,23 @@ start_port(portid_t pid)
 				port->need_reconfig = 1;
 				return -1;
 			}
+
+			/*
+			 * Workaround for rte_eth_dev_configure(), max_rx_pkt_len
+			 * set MTU wrong for the PMDs that have frame overhead
+			 * bigger than RTE_ETHER_HDR_LEN + RTE_ETHER_CRC_LEN.
+			 * For a PMD that has 26 bytes overhead, rte_eth_dev_configure()
+			 * can set MTU to max 1492, not to expected 1500 bytes.
+			 * Using rte_eth_dev_set_mtu() to be able to set MTU correctly,
+			 * default MTU value is 1500.
+			 */
+			diag = rte_eth_dev_get_mtu(pi, &mtu);
+			if (diag)
+				printf("Failed to get MTU for port %d\n", pi);
+			diag = rte_eth_dev_set_mtu(pi, mtu);
+			if (diag != 0 && diag != -ENOTSUP)
+				printf("Failed to set MTU to %u for port %d\n",
+						mtu, pi);
 		}
 		if (port->need_reconfig_queues > 0) {
 			port->need_reconfig_queues = 0;
-- 
2.26.2