From: Andrew Lunn <andrew@lunn.ch>

When performing a C22 operation, check that the bus driver actually
provides the methods, and return -EOPNOTSUPP if not. C45 only busses
do exist, and in future their C22 methods will be NULL.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Michael Walle <michael@walle.cc>
---
 drivers/net/phy/mdio_bus.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/phy/mdio_bus.c b/drivers/net/phy/mdio_bus.c
index d14d7704e895..20ba38a346fe 100644
--- a/drivers/net/phy/mdio_bus.c
+++ b/drivers/net/phy/mdio_bus.c
@@ -769,7 +769,10 @@ int __mdiobus_read(struct mii_bus *bus, int addr, u32 regnum)
 
 	lockdep_assert_held_once(&bus->mdio_lock);
 
-	retval = bus->read(bus, addr, regnum);
+	if (bus->read)
+		retval = bus->read(bus, addr, regnum);
+	else
+		retval = -EOPNOTSUPP;
 
 	trace_mdio_access(bus, 1, addr, regnum, retval, retval);
 	mdiobus_stats_acct(&bus->stats[addr], true, retval);
@@ -795,7 +798,10 @@ int __mdiobus_write(struct mii_bus *bus, int addr, u32 regnum, u16 val)
 
 	lockdep_assert_held_once(&bus->mdio_lock);
 
-	err = bus->write(bus, addr, regnum, val);
+	if (bus->write)
+		err = bus->write(bus, addr, regnum, val);
+	else
+		err = -EOPNOTSUPP;
 
 	trace_mdio_access(bus, 0, addr, regnum, val, err);
 	mdiobus_stats_acct(&bus->stats[addr], false, err);

-- 
2.30.2