linux-kernel - [PATCH 3/5] net: dsa: b53: fix max MTU for BCM5325/BCM5365

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Message-Id: <20241004-b53_jumbo_fixes-v1-3-ce1e54aa7b3c@gmail.com>
Date: Fri, 04 Oct 2024 10:47:19 +0200
From: Jonas Gorski <jonas.gorski@...il.com>
To: Florian Fainelli <florian.fainelli@...adcom.com>, 
 Andrew Lunn <andrew@...n.ch>, Vladimir Oltean <olteanv@...il.com>, 
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
 Murali Krishna Policharla <murali.policharla@...adcom.com>, 
 Russell King <linux@...linux.org.uk>
Cc: Florian Fainelli <f.fainelli@...il.com>, 
 Vladimir Oltean <vladimir.oltean@....com>, netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org
Subject: [PATCH 3/5] net: dsa: b53: fix max MTU for BCM5325/BCM5365

BCM5325/BCM5365 do not support jumbo frames, so we should not report a
jumbo frame mtu for them. But they do support so called "oversized"
frames up to 1536 bytes long by default, so report an appropriate MTU.

Fixes: 6ae5834b983a ("net: dsa: b53: add MTU configuration support")
Signed-off-by: Jonas Gorski <jonas.gorski@...il.com>
---
 drivers/net/dsa/b53/b53_common.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/dsa/b53/b53_common.c b/drivers/net/dsa/b53/b53_common.c
index 6fed3eb15ad9b257c6fc3da20ce91b5e7129884c..e8b20bfa8b83ea7ac643bd5d005e2983747bd478 100644
--- a/drivers/net/dsa/b53/b53_common.c
+++ b/drivers/net/dsa/b53/b53_common.c
@@ -225,6 +225,7 @@ static const struct b53_mib_desc b53_mibs_58xx[] = {

 #define B53_MIBS_58XX_SIZE	ARRAY_SIZE(b53_mibs_58xx)

+#define B53_MAX_MTU_25		(1536 - ETH_HLEN - VLAN_HLEN - ETH_FCS_LEN)
 #define B53_MAX_MTU		(9720 - ETH_HLEN - VLAN_HLEN - ETH_FCS_LEN)

 static int b53_do_vlan_op(struct b53_device *dev, u8 op)
@@ -2270,6 +2271,11 @@ static int b53_change_mtu(struct dsa_switch *ds, int port, int mtu)

 static int b53_get_max_mtu(struct dsa_switch *ds, int port)
 {
+	struct b53_device *dev = ds->priv;
+
+	if (is5325(dev) || is5365(dev))
+		return B53_MAX_MTU_25;
+
 	return B53_MAX_MTU;
 }

-- 
2.43.0