net/enic: fix max MTU calculation

Message ID 20190314110532.22638-1-hyonkim@cisco.com
State Accepted, archived
Delegated to: Ferruh Yigit
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Series
  • net/enic: fix max MTU calculation
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Checks

Context Check Description
ci/Intel-compilation success Compilation OK
ci/intel-Performance-Testing success Performance Testing PASS
ci/mellanox-Performance-Testing success Performance Testing PASS
ci/checkpatch success coding style OK

Commit Message

Hyong Youb Kim (hyonkim) March 14, 2019, 11:05 a.m.
The maximum packet length (max_pkt_len) from the firmware does not
include CRC, so do not subtract 4 when deriving the max MTU. This
change effectively increases the max MTU by 4B. Apps often assume max
MTU = max_rx_pkt_len - 14 (ethernet header), and attempt to set the
MTU to that value (i.e. set MTU to max HW value). This change
incidentally allows such apps to change MTU to max value successfully.

Fixes: bb34ffb848a0 ("net/enic: determine max egress packet size and max MTU")
Cc: stable@dpdk.org

Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
Reviewed-by: John Daley <johndale@cisco.com>
---
 drivers/net/enic/enic.h     | 4 ++--
 drivers/net/enic/enic_res.c | 5 ++---
 2 files changed, 4 insertions(+), 5 deletions(-)

Comments

Ferruh Yigit March 20, 2019, 2:30 p.m. | #1
On 3/14/2019 11:05 AM, Hyong Youb Kim wrote:
> The maximum packet length (max_pkt_len) from the firmware does not
> include CRC, so do not subtract 4 when deriving the max MTU. This
> change effectively increases the max MTU by 4B. Apps often assume max
> MTU = max_rx_pkt_len - 14 (ethernet header), and attempt to set the
> MTU to that value (i.e. set MTU to max HW value). This change
> incidentally allows such apps to change MTU to max value successfully.
> 
> Fixes: bb34ffb848a0 ("net/enic: determine max egress packet size and max MTU")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Hyong Youb Kim <hyonkim@cisco.com>
> Reviewed-by: John Daley <johndale@cisco.com>

Applied to dpdk-next-net/master, thanks.

Patch

diff --git a/drivers/net/enic/enic.h b/drivers/net/enic/enic.h
index fa4d5590e..9193fb038 100644
--- a/drivers/net/enic/enic.h
+++ b/drivers/net/enic/enic.h
@@ -203,8 +203,8 @@  struct enic {
 /* Compute ethdev's max packet size from MTU */
 static inline uint32_t enic_mtu_to_max_rx_pktlen(uint32_t mtu)
 {
-	/* ethdev max size includes eth and crc whereas NIC MTU does not */
-	return mtu + ETHER_HDR_LEN + ETHER_CRC_LEN;
+	/* ethdev max size includes eth whereas NIC MTU does not */
+	return mtu + ETHER_HDR_LEN;
 }
 
 /* Get the CQ index from a Start of Packet(SOP) RQ index */
diff --git a/drivers/net/enic/enic_res.c b/drivers/net/enic/enic_res.c
index d289f3da8..f7cbc90fb 100644
--- a/drivers/net/enic/enic_res.c
+++ b/drivers/net/enic/enic_res.c
@@ -61,10 +61,9 @@  int enic_get_vnic_config(struct enic *enic)
 	 * and will be 0 for legacy firmware and VICs
 	 */
 	if (c->max_pkt_size > ENIC_DEFAULT_RX_MAX_PKT_SIZE)
-		enic->max_mtu = c->max_pkt_size - (ETHER_HDR_LEN + 4);
+		enic->max_mtu = c->max_pkt_size - ETHER_HDR_LEN;
 	else
-		enic->max_mtu = ENIC_DEFAULT_RX_MAX_PKT_SIZE
-				- (ETHER_HDR_LEN + 4);
+		enic->max_mtu = ENIC_DEFAULT_RX_MAX_PKT_SIZE - ETHER_HDR_LEN;
 	if (c->mtu == 0)
 		c->mtu = 1500;