netdev - [PATCH net-next] mvpp2: document HW checksum behaviour

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Message-Id: <20190725231546.23878-1-mcroce@redhat.com>
Date:   Fri, 26 Jul 2019 01:15:46 +0200
From:   Matteo Croce <mcroce@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Antoine Tenart <antoine.tenart@...tlin.com>,
        Maxime Chevallier <maxime.chevallier@...tlin.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Stefan Chulski <stefanc@...vell.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH net-next] mvpp2: document HW checksum behaviour

The hardware can only offload checksum calculation on first port due to
the Tx FIFO size limitation. Document this in a comment.

Fixes: 576193f2d579 ("net: mvpp2: jumbo frames support")
Signed-off-by: Matteo Croce <mcroce@...hat.com>
---
 drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
index d8e5241097a9..2f7286bd203b 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c
@@ -843,7 +843,10 @@ static int mvpp2_bm_update_mtu(struct net_device *dev, int mtu)
 		/* Add port to new short & long pool */
 		mvpp2_swf_bm_pool_init(port);
 
-		/* Update L4 checksum when jumbo enable/disable on port */
+		/* Update L4 checksum when jumbo enable/disable on port.
+		 * Only port 0 supports hardware checksum offload due to
+		 * the Tx FIFO size limitation.
+		 */
 		if (new_long_pool == MVPP2_BM_JUMBO && port->id != 0) {
 			dev->features &= ~(NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM);
 			dev->hw_features &= ~(NETIF_F_IP_CSUM |
-- 
2.21.0