netdev - [PATCH net-next 2/2] net: mdio-mux: be compatible with parent buses which only support C45

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Message-Id: <20231213152712.320842-3-vladimir.oltean@nxp.com>
Date: Wed, 13 Dec 2023 17:27:12 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: netdev@...r.kernel.org
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>,
	Andrew Lunn <andrew@...n.ch>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>
Subject: [PATCH net-next 2/2] net: mdio-mux: be compatible with parent buses which only support C45

After the mii_bus API conversion to a split read() / read_c45(), there
might be MDIO parent buses which only populate the read_c45() and
write_c45() function pointers but not the C22 variants.

We haven't seen these in the wild paired with MDIO multiplexers, but
Andrew points out we should treat the corner case.

Link: https://lore.kernel.org/netdev/4ccd7dc9-b611-48aa-865f-68d3a1327ce8@lunn.ch/
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/mdio/mdio-mux.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/mdio/mdio-mux.c b/drivers/net/mdio/mdio-mux.c
index e5dee7ad7c09..fe0e46bd7964 100644
--- a/drivers/net/mdio/mdio-mux.c
+++ b/drivers/net/mdio/mdio-mux.c
@@ -214,8 +214,10 @@ int mdio_mux_init(struct device *dev,
 		snprintf(cb->mii_bus->id, MII_BUS_ID_SIZE, "%s-%x.%x",
 			 cb->mii_bus->name, pb->parent_id, v);
 		cb->mii_bus->parent = dev;
-		cb->mii_bus->read = mdio_mux_read;
-		cb->mii_bus->write = mdio_mux_write;
+		if (parent_bus->read)
+			cb->mii_bus->read = mdio_mux_read;
+		if (parent_bus->write)
+			cb->mii_bus->write = mdio_mux_write;
 		if (parent_bus->read_c45)
 			cb->mii_bus->read_c45 = mdio_mux_read_c45;
 		if (parent_bus->write_c45)
-- 
2.34.1