[PATCH 5.15 638/691] net: dsa: b53: fix max MTU for BCM5325/BCM5365

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5.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jonas Gorski <jonas.gorski@xxxxxxxxx>

[ Upstream commit ca8c1f71c10193c270f772d70d34b15ad765d6a8 ]

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@xxxxxxxxx>
Reviewed-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 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 be1550332326a..3aa0a60d7c71e 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)
@@ -2237,6 +2238,11 @@ 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







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