net: dsa: sja1105: disallow C45 transactions on the BASE-TX MDIO bus

You'd think people know that the internal 100BASE-TX PHY on the SJA1110
responds only to clause 22 MDIO transactions, but they don't :)

When a clause 45 transaction is attempted, sja1105_base_tx_mdio_read()
and sja1105_base_tx_mdio_write() don't expect "reg" to contain bit 30
set (MII_ADDR_C45) and pack this value into the SPI transaction buffer.

But the field in the SPI buffer has a width smaller than 30 bits, so we
see this confusing message from the packing() API rather than a proper
rejection of C45 transactions:

Call trace:
 dump_stack+0x1c/0x38
 sja1105_pack+0xbc/0xc0 [sja1105]
 sja1105_xfer+0x114/0x2b0 [sja1105]
 sja1105_xfer_u32+0x44/0xf4 [sja1105]
 sja1105_base_tx_mdio_read+0x44/0x7c [sja1105]
 mdiobus_read+0x44/0x80
 get_phy_c45_ids+0x70/0x234
 get_phy_device+0x68/0x15c
 fwnode_mdiobus_register_phy+0x74/0x240
 of_mdiobus_register+0x13c/0x380
 sja1105_mdiobus_register+0x368/0x490 [sja1105]
 sja1105_setup+0x94/0x119c [sja1105]
Cannot store 401d2405 inside bits 24-4 (would truncate)

Fixes: 5a8f0974 ("net: dsa: sja1105: register the MDIO buses for 100base-T1 and 100base-TX")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/sja1105/sja1105_mdio.c

@@ -256,6 +256,9 @@ static int sja1105_base_tx_mdio_read(struct mii_bus *bus, int phy, int reg)
 	u32 tmp;
 	int rc;
 
+	if (reg & MII_ADDR_C45)
+		return -EOPNOTSUPP;
+
 	rc = sja1105_xfer_u32(priv, SPI_READ, regs->mdio_100base_tx + reg,
 			      &tmp, NULL);
 	if (rc < 0)
@@ -272,6 +275,9 @@ static int sja1105_base_tx_mdio_write(struct mii_bus *bus, int phy, int reg,
 	const struct sja1105_regs *regs = priv->info->regs;
 	u32 tmp = val;
 
+	if (reg & MII_ADDR_C45)
+		return -EOPNOTSUPP;
+
 	return sja1105_xfer_u32(priv, SPI_WRITE, regs->mdio_100base_tx + reg,
 				&tmp, NULL);
 }