From: Julian Wiedmann <jwi@linux.ibm.com>
Subject: s390/qeth: clean up initial MTU determination
Patch-mainline: v4.15-rc1
Git-commit: 6e6f472d92bd4ccd88a9a12e55b484ab417c168c
References: FATE#326350, LTC#169511, bsc#1113509

Summary:     qeth: performance improvements
Description: This adds recent functional and performance improvements for the
             qeth network driver.
             Primarily this brings Scatter-Gather support for HiperSockets,
             reduced CPU consumption in the L3 IPv4 transmit path for OSA,
             improved Promiscuous Mode performance due to IFF_UNICAST_FLT,
             support for Scatter-Gather on z/VM virtual NICs, and
             support for delayed GRO flushing.

             For sanity & stability reasons, this effectively constitutes a
             backport of the qeth device driver from 4.19 mainline.
             

Upstream-Description:

             s390/qeth: clean up initial MTU determination

             1. Drop the support for Token Ring,
             2. use the ETH_DATA_LEN macro for the default L2 MTU,
             3. handle OSM via the default case (as OSM is L2-only), and
             4. document why the L3 MTU is reduced.

             Signed-off-by: Julian Wiedmann <jwi@linux.vnet.ibm.com>
             Signed-off-by: David S. Miller <davem@davemloft.net>

Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Acked-by: Petr Tesarik <ptesarik@suse.com>
---
 drivers/s390/net/qeth_core_main.c |   14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

--- a/drivers/s390/net/qeth_core_main.c
+++ b/drivers/s390/net/qeth_core_main.c
@@ -2243,18 +2243,12 @@ static int qeth_get_initial_mtu_for_card
 	case QETH_CARD_TYPE_IQD:
 		return card->info.max_mtu;
 	case QETH_CARD_TYPE_OSD:
-		switch (card->info.link_type) {
-		case QETH_LINK_TYPE_HSTR:
-		case QETH_LINK_TYPE_LANE_TR:
-			return 2000;
-		default:
-			return card->options.layer2 ? 1500 : 1492;
-		}
-	case QETH_CARD_TYPE_OSM:
 	case QETH_CARD_TYPE_OSX:
-		return card->options.layer2 ? 1500 : 1492;
+		if (!card->options.layer2)
+			return ETH_DATA_LEN - 8; /* L3: allow for LLC + SNAP */
+		/* fall through */
 	default:
-		return 1500;
+		return ETH_DATA_LEN;
 	}
 }