netdev - [PATCH net v2 1/2] net: dsa: mv88e6xxx: Limit chip-wide frame size config to CPU ports

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Message-ID: <20240717090820.894234-2-martin@strongswan.org>
Date: Wed, 17 Jul 2024 11:08:19 +0200
From: Martin Willi <martin@...ongswan.org>
To: Andrew Lunn <andrew@...n.ch>,
	Florian Fainelli <f.fainelli@...il.com>,
	Vladimir Oltean <olteanv@...il.com>,
	Chris Packham <chris.packham@...iedtelesis.co.nz>,
	Murali Krishna Policharla <murali.policharla@...adcom.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	netdev@...r.kernel.org
Subject: [PATCH net v2 1/2] net: dsa: mv88e6xxx: Limit chip-wide frame size config to CPU ports

Marvell chips not supporting per-port jumbo frame size configurations use
a chip-wide frame size configuration. In the commit referenced with the
Fixes tag, the setting is applied just for the last port changing its MTU.

While configuring CPU ports accounts for tagger overhead, user ports do
not. When setting the MTU for a user port, the chip-wide setting is
reduced to not include the tagger overhead, resulting in an potentially
insufficient maximum frame size for the CPU port. Specifically, sending
full-size frames from the CPU port on a MV88E6097 having a user port MTU
of 1500 bytes results in dropped frames.

As, by design, the CPU port MTU is adjusted for any user port change,
apply the chip-wide setting only for CPU ports.

Fixes: 1baf0fac10fb ("net: dsa: mv88e6xxx: Use chip-wide max frame size for MTU")
Suggested-by: Vladimir Oltean <olteanv@...il.com>
Signed-off-by: Martin Willi <martin@...ongswan.org>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 07c897b13de1..5b4e2ce5470d 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -3626,7 +3626,8 @@ static int mv88e6xxx_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
 	mv88e6xxx_reg_lock(chip);
 	if (chip->info->ops->port_set_jumbo_size)
 		ret = chip->info->ops->port_set_jumbo_size(chip, port, new_mtu);
-	else if (chip->info->ops->set_max_frame_size)
+	else if (chip->info->ops->set_max_frame_size &&
+		 dsa_is_cpu_port(ds, port))
 		ret = chip->info->ops->set_max_frame_size(chip, new_mtu);
 	mv88e6xxx_reg_unlock(chip);

-- 
2.43.0