linux-kernel - [PATCH net-next v2 1/1] net: macb: fix negative max

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Message-Id: <20220617071607.3782772-1-o.rempel@pengutronix.de>
Date:   Fri, 17 Jun 2022 09:16:07 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Oleksij Rempel <o.rempel@...gutronix.de>, kernel@...gutronix.de,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH net-next v2 1/1] net: macb: fix negative max_mtu size for sama5d3

JML register on probe will return zero . This register is configured
later on macb_init_hw() which is called on open.
Since we have zero, after header and FCS length subtraction we will get
negative max_mtu size. This issue was affecting DSA drivers with MTU support
(for example KSZ9477).

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
changes v2:
- properly describe fail reason
- simplify max_mtu logic

 drivers/net/ethernet/cadence/macb_main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
index d89098f4ede8..d0ea8dbfa213 100644
--- a/drivers/net/ethernet/cadence/macb_main.c
+++ b/drivers/net/ethernet/cadence/macb_main.c
@@ -4913,8 +4913,8 @@ static int macb_probe(struct platform_device *pdev)
 
 	/* MTU range: 68 - 1500 or 10240 */
 	dev->min_mtu = GEM_MTU_MIN_SIZE;
-	if (bp->caps & MACB_CAPS_JUMBO)
-		dev->max_mtu = gem_readl(bp, JML) - ETH_HLEN - ETH_FCS_LEN;
+	if ((bp->caps & MACB_CAPS_JUMBO) && bp->jumbo_max_len)
+		dev->max_mtu = bp->jumbo_max_len - ETH_HLEN - ETH_FCS_LEN;
 	else
 		dev->max_mtu = ETH_DATA_LEN;
 
-- 
2.30.2