netdev - [PATCH net] net: dsa: mv88e6xxx: prevent interrupt storm caused by mv88e6390x_port_set

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Message-ID: <864ac062-51cb-ec9e-388b-b74a62eb6e6a@gmail.com>
Date:   Wed, 27 Feb 2019 20:55:22 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Vivien Didelot <vivien.didelot@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: [PATCH net] net: dsa: mv88e6xxx: prevent interrupt storm caused by
 mv88e6390x_port_set_cmode

When debugging another issue I faced an interrupt storm in this
driver (88E6390, port 9 in SGMII mode), consisting of alternating
link-up / link-down interrupts. Analysis showed that the driver
wanted to set a cmode that was set already. But so far
mv88e6390x_port_set_cmode() doesn't check this and powers down
SERDES, what causes the link to break, and eventually results in
the described interrupt storm.

Fix this by checking whether the cmode actually changes. We want
that the very first call to mv88e6390x_port_set_cmode() always
configures the registers, therefore initialize port.cmode with
a value that is different from any supported cmode value.

Fixes: 364e9d7776a3 ("net: dsa: mv88e6xxx: Power on/off SERDES on cmode change")
Signed-off-by: Heiner Kallweit <hkallweit1@...il.com>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 4 ++++
 drivers/net/dsa/mv88e6xxx/port.c | 4 ++++
 drivers/net/dsa/mv88e6xxx/port.h | 1 +
 3 files changed, 9 insertions(+)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 32e7af5ca..d4edb61e8 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -4568,6 +4568,7 @@ static int mv88e6xxx_detect(struct mv88e6xxx_chip *chip)
 static struct mv88e6xxx_chip *mv88e6xxx_alloc_chip(struct device *dev)
 {
 	struct mv88e6xxx_chip *chip;
+	int i;
 
 	chip = devm_kzalloc(dev, sizeof(*chip), GFP_KERNEL);
 	if (!chip)
@@ -4578,6 +4579,9 @@ static struct mv88e6xxx_chip *mv88e6xxx_alloc_chip(struct device *dev)
 	mutex_init(&chip->reg_lock);
 	INIT_LIST_HEAD(&chip->mdios);
 
+	for (i = 0; i < ARRAY_SIZE(chip->ports); i++)
+		chip->ports[i].cmode = MV88E6XXX_PORT_STS_CMODE_INVALID;
+
 	return chip;
 }
 
diff --git a/drivers/net/dsa/mv88e6xxx/port.c b/drivers/net/dsa/mv88e6xxx/port.c
index ebd26b6a9..70b7a1463 100644
--- a/drivers/net/dsa/mv88e6xxx/port.c
+++ b/drivers/net/dsa/mv88e6xxx/port.c
@@ -398,6 +398,10 @@ int mv88e6390x_port_set_cmode(struct mv88e6xxx_chip *chip, int port,
 		cmode = 0;
 	}
 
+	/* cmode doesn't change, nothing to do for us */
+	if (cmode == chip->ports[port].cmode)
+		return 0;
+
 	lane = mv88e6390x_serdes_get_lane(chip, port);
 	if (lane < 0)
 		return lane;
diff --git a/drivers/net/dsa/mv88e6xxx/port.h b/drivers/net/dsa/mv88e6xxx/port.h
index e583641de..4aadf321e 100644
--- a/drivers/net/dsa/mv88e6xxx/port.h
+++ b/drivers/net/dsa/mv88e6xxx/port.h
@@ -52,6 +52,7 @@
 #define MV88E6185_PORT_STS_CMODE_1000BASE_X	0x0005
 #define MV88E6185_PORT_STS_CMODE_PHY		0x0006
 #define MV88E6185_PORT_STS_CMODE_DISABLED	0x0007
+#define MV88E6XXX_PORT_STS_CMODE_INVALID	0xff
 
 /* Offset 0x01: MAC (or PCS or Physical) Control Register */
 #define MV88E6XXX_PORT_MAC_CTL				0x01
-- 
2.21.0