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

[Andrew Lunn]

On Wed, Aug 16, 2023 at 09:06:52PM +0300, Serge Semin wrote:
> 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.

I'm actually surprised we have not got more reports of me breaking
MDIO with this patchset. I did test bit-banging, but only for C22.

> Fixes: 002dd3de097c ("net: mdio: mdio-bitbang: Separate C22 and C45 transactions")
> Signed-off-by: Serge Semin <fancer.lancer@xxxxxxxxx>

Reviewed-by: Andrew Lunn <andrew@xxxxxxx>

    Andrew