netdev - Re: [PATCH net] net: dsa: sja1105: disallow C45 transactions on the BASE-TX MDIO bus

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Date:   Wed, 16 Nov 2022 14:28:20 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net] net: dsa: sja1105: disallow C45 transactions on the
 BASE-TX MDIO bus

On Wed, Nov 16, 2022 at 12:06:53PM +0200, Vladimir Oltean wrote:
> 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.

Yep, it is a common problem with MDIO busses. And driver i review now
i asks for EOPNOTSUPP for clauses which are not supported, but there
are old drivers out there missing such checks.

I have a bit rotting patchset which completely separates C22 and C45,
i just spend too much time reviewing other code to get my own merged.

> Fixes: 5a8f09748ee7 ("net: dsa: sja1105: register the MDIO buses for 100base-T1 and 100base-TX")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Andrew Lunn <andrew@...n.ch>

    Andrew