[PATCH] net: dsa: mv88e6xxx: Make *_c45 callbacks agree with phy_*_c45 callbacks

[Tim Menninger <tmenninger@purestorage.com>]

Set the read_c45 callback in the mii_bus struct in mv88e6xxx only if there
is a non-NULL phy_read_c45 callback on the chip mv88e6xxx_ops. Similarly
for write_c45 and phy_write_c45.

In commit 743a19e38d02 ("net: dsa: mv88e6xxx: Separate C22 and C45 transactions")
the MDIO bus driver split its API to separate C22 and C45 transfers.

In commit 1a136ca2e089 ("net: mdio: scan bus based on bus capabilities for C22 and C45")
we do a C45 mdio bus scan based on existence of the read_c45 callback
rather than checking MDIO bus capabilities then in
commit da099a7fb13d ("net: phy: Remove probe_capabilities") we remove the
probe_capabilities from the mii_bus struct.

The combination of the above results in a scenario (e.g. mv88e6185)
where we take a non-NULL read_c45 callback on the mii_bus struct to mean
we can perform a C45 read and proceed with a C45 MDIO bus scan. The scan
encounters a NULL phy_read_c45 callback in the mv88e6xxx_ops which implies
we can NOT perform a C45 read and fails with EOPNOTSUPP. The read_c45
callback should be NULL if phy_read_c45 is NULL, and similarly for
write_c45 and phy_write_c45.

Fixes: 1a136ca2e089 ("net: mdio: scan bus based on bus capabilities for C22 and C45")
Fixes: da099a7fb13d ("net: phy: Remove probe_capabilities")

Signed-off-by: Tim Menninger <tmenninger@purestorage.com>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 383b3c4d6f59..ba972d5427e5 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -3739,8 +3739,10 @@ static int mv88e6xxx_mdio_register(struct mv88e6xxx_chip *chip,
 
 	bus->read = mv88e6xxx_mdio_read;
 	bus->write = mv88e6xxx_mdio_write;
-	bus->read_c45 = mv88e6xxx_mdio_read_c45;
-	bus->write_c45 = mv88e6xxx_mdio_write_c45;
+	bus->read_c45 = chip->info->ops->phy_read_c45
+		? mv88e6xxx_mdio_read_c45 : NULL;
+	bus->write_c45 = chip->info->ops->phy_write_c45
+		? mv88e6xxx_mdio_write_c45 : NULL;
 	bus->parent = chip->dev;
 	bus->phy_mask = ~GENMASK(chip->info->phy_base_addr +
 				 mv88e6xxx_num_ports(chip) - 1,
-- 
2.34.1