linux-kernel - [PATCH] net: dsa: mv88e6060: Fix false positive lockdep splat

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Message-ID: <5627B149.6030109@baylibre.com>
Date:	Wed, 21 Oct 2015 17:37:45 +0200
From:	Neil Armstrong <narmstrong@...libre.com>
To:	"David S. Miller" <davem@...emloft.net>,
	Florian Fainelli <f.fainelli@...il.com>,
	Guenter Roeck <linux@...ck-us.net>,
	vivien.didelot@...oirfairelinux.com, Andrew Lunn <andrew@...n.ch>,
	Fabian Frederick <fabf@...net.be>,
	Pavel Nakonechny <pavel.nakonechny@...tlab.ru>,
	Joe Perches <joe@...ches.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, nbd@...nwrt.org,
	sergei.shtylyov@...entembedded.com
Subject: [PATCH] net: dsa: mv88e6060: Fix false positive lockdep splat

Like the change made for mv88e6xxx, use mutex_lock_nested() to avoid
lockdep to give false positives because of nested MDIO busses.

The false positive was observed using a mv88e6060 from a TI816X SoC.

Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
---
 drivers/net/dsa/mv88e6060.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/mv88e6060.c b/drivers/net/dsa/mv88e6060.c
index c29aebe..b1db460 100644
--- a/drivers/net/dsa/mv88e6060.c
+++ b/drivers/net/dsa/mv88e6060.c
@@ -19,14 +19,24 @@
 #define REG_PORT(p)		(8 + (p))
 #define REG_GLOBAL		0x0f

+/* MDIO bus access can be nested in the case of PHYs connected to the
+ * internal MDIO bus of the switch, which is accessed via MDIO bus of
+ * the Ethernet interface. Avoid lockdep false positives by using
+ * mutex_lock_nested().
+ */
 static int reg_read(struct dsa_switch *ds, int addr, int reg)
 {
+	int ret;
 	struct mii_bus *bus = dsa_host_dev_to_mii_bus(ds->master_dev);

 	if (bus == NULL)
 		return -EINVAL;

-	return mdiobus_read(bus, ds->pd->sw_addr + addr, reg);
+	mutex_lock_nested(&bus->mdio_lock, SINGLE_DEPTH_NESTING);
+	ret = bus->read(bus, ds->pd->sw_addr, reg);
+	mutex_unlock(&bus->mdio_lock);
+
+	return ret;
 }

 #define REG_READ(addr, reg)					\
@@ -42,12 +52,17 @@ static int reg_read(struct dsa_switch *ds, int addr, int reg)

 static int reg_write(struct dsa_switch *ds, int addr, int reg, u16 val)
 {
+	int ret;
 	struct mii_bus *bus = dsa_host_dev_to_mii_bus(ds->master_dev);

 	if (bus == NULL)
 		return -EINVAL;

-	return mdiobus_write(bus, ds->pd->sw_addr + addr, reg, val);
+	mutex_lock_nested(&bus->mdio_lock, SINGLE_DEPTH_NESTING);
+	ret = bus->write(bus, ds->pd->sw_addr, reg, val);
+	mutex_unlock(&bus->mdio_lock);
+
+	return ret;
 }

 #define REG_WRITE(addr, reg, val)				\
-- 
1.9.1

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