netdev - [PATCH net] net: dsa: mv88e6xxx: Respect other ports when setting chip-wide MTU

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Message-ID: <20240716120808.396514-1-martin@strongswan.org>
Date: Tue, 16 Jul 2024 14:08:08 +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>
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] net: dsa: mv88e6xxx: Respect other ports when setting chip-wide MTU

DSA chips not supporting per-port jumbo frame size configurations use a
chip-wide setting. In the commit referenced with the Fixes tag, the
setting is applied just for the last port changing its MTU. This may
result in two issues:

  * Starting with commit b9c587fed61c ("dsa: mv88e6xxx: Include tagger
    overhead when setting MTU for DSA and CPU ports"), the CPU port
    accounts for tagger overhead. If a user port is configured after
    the CPU port, the chip-wide setting may be reduced again, as the
    user port does not account for tagger overhead.
  * If different user ports use different MTUs (say within different
    L2 domains), setting the lower MTU after the higher MTU may result
    in a chip-wide setting for the lower MTU, only.

Any of the above may result in clearing MV88E6185_G1_CTL1_MAX_FRAME_1632
while it is actually required for the current configuration on some (CPU)
ports. Specifically, on a MV88E6097 this results in dropped frames when
setting the MTU to 1500 and sending local full-sized frames over a user
port.

To respect the MTU requirements of all CPU and user ports, get the maximum
frame size requirements over all ports when updating the chip-wide
setting.

Fixes: 1baf0fac10fb ("net: dsa: mv88e6xxx: Use chip-wide max frame size for MTU")
Signed-off-by: Martin Willi <martin@...ongswan.org>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 07c897b13de1..c231c956bf9a 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -3604,9 +3604,19 @@ static int mv88e6xxx_get_max_mtu(struct dsa_switch *ds, int port)
 	return ETH_DATA_LEN;
 }
 
+static int mv88e6xxx_get_port_mtu(struct dsa_port *dp)
+{
+	if (dsa_port_is_cpu(dp))
+		return dp->conduit->mtu;
+	if (dsa_port_is_user(dp) && dp->user)
+		return dp->user->mtu;
+	return 0;
+}
+
 static int mv88e6xxx_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
 {
 	struct mv88e6xxx_chip *chip = ds->priv;
+	struct dsa_port *dp;
 	int ret = 0;
 
 	/* For families where we don't know how to alter the MTU,
@@ -3626,8 +3636,14 @@ 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_switch_for_each_port(dp, ds) {
+			if (dp->index == port)
+				continue;
+			new_mtu = max(new_mtu, mv88e6xxx_get_port_mtu(dp));
+		}
 		ret = chip->info->ops->set_max_frame_size(chip, new_mtu);
+	}
 	mv88e6xxx_reg_unlock(chip);
 
 	return ret;
-- 
2.43.0