linux-kernel - [PATCH net] net: mdio: mdio-bitbang: Fix C45 read/write protocol

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Date:   Wed, 16 Aug 2023 21:06:52 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Michael Walle <michael@...le.cc>
Cc:     Serge Semin <fancer.lancer@...il.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net] net: mdio: mdio-bitbang: Fix C45 read/write protocol

Based on the original code semantic in case of Clause 45 MDIO, the address
command is supposed to be followed by the command sending the MMD address,
not the CSR address. The commit 002dd3de097c ("net: mdio: mdio-bitbang:
Separate C22 and C45 transactions") has erroneously broken that. So most
likely due to an unfortunate variable name it switched the code to sending
the CSR address. In our case it caused the protocol malfunction so the
read operation always failed with the turnaround bit always been driven to
one by PHY instead of zero. Fix that by getting back the correct
behaviour: sending MMD address command right after the regular address
command.

Fixes: 002dd3de097c ("net: mdio: mdio-bitbang: Separate C22 and C45 transactions")
Signed-off-by: Serge Semin <fancer.lancer@...il.com>
---
 drivers/net/mdio/mdio-bitbang.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/mdio/mdio-bitbang.c b/drivers/net/mdio/mdio-bitbang.c
index b83932562be2..81b7748c10ce 100644
--- a/drivers/net/mdio/mdio-bitbang.c
+++ b/drivers/net/mdio/mdio-bitbang.c
@@ -186,7 +186,7 @@ int mdiobb_read_c45(struct mii_bus *bus, int phy, int devad, int reg)
 	struct mdiobb_ctrl *ctrl = bus->priv;
 
 	mdiobb_cmd_addr(ctrl, phy, devad, reg);
-	mdiobb_cmd(ctrl, MDIO_C45_READ, phy, reg);
+	mdiobb_cmd(ctrl, MDIO_C45_READ, phy, devad);
 
 	return mdiobb_read_common(bus, phy);
 }
@@ -222,7 +222,7 @@ int mdiobb_write_c45(struct mii_bus *bus, int phy, int devad, int reg, u16 val)
 	struct mdiobb_ctrl *ctrl = bus->priv;
 
 	mdiobb_cmd_addr(ctrl, phy, devad, reg);
-	mdiobb_cmd(ctrl, MDIO_C45_WRITE, phy, reg);
+	mdiobb_cmd(ctrl, MDIO_C45_WRITE, phy, devad);
 
 	return mdiobb_write_common(bus, val);
 }
-- 
2.41.0