netdev - Re: [PATCH net] net: mdio-mux: fix C45 access returning -EIO after API change

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Message-ID: <ZS6Mskpb6gDpBD3z@shell.armlinux.org.uk>
Date: Tue, 17 Oct 2023 14:31:30 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Vladimir Oltean <vladimir.oltean@....com>
Cc: netdev@...r.kernel.org, "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>,
	Florian Fainelli <f.fainelli@...il.com>,
	Michael Walle <michael@...le.cc>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: mdio-mux: fix C45 access returning -EIO after
 API change

On Tue, Oct 17, 2023 at 02:32:22PM +0300, Vladimir Oltean wrote:
> The mii_bus API conversion to read_c45() and write_c45() did not cover
> the mdio-mux driver before read() and write() were made C22-only.
> 
> This broke arch/arm64/boot/dts/freescale/fsl-ls1028a-qds-13bb.dtso.
> The -EOPNOTSUPP from mdiobus_c45_read() is transformed by
> get_phy_c45_devs_in_pkg() into -EIO, is further propagated to
> of_mdiobus_register() and this makes the mdio-mux driver fail to probe
> the entire child buses, not just the PHYs that cause access errors.
> 
> Fix the regression by introducing special c45 read and write accessors
> to mdio-mux which forward the operation to the parent MDIO bus.
> 
> Fixes: db1a63aed89c ("net: phy: Remove fallback to old C45 method")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
>  drivers/net/mdio/mdio-mux.c | 45 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
> 
> diff --git a/drivers/net/mdio/mdio-mux.c b/drivers/net/mdio/mdio-mux.c
> index a881e3523328..7d322c08c1e9 100644
> --- a/drivers/net/mdio/mdio-mux.c
> +++ b/drivers/net/mdio/mdio-mux.c
> @@ -55,6 +55,27 @@ static int mdio_mux_read(struct mii_bus *bus, int phy_id, int regnum)
>  	return r;
>  }
>  
> +static int mdio_mux_read_c45(struct mii_bus *bus, int phy_id, int dev_addr,
> +			     int regnum)
> +{
> +	struct mdio_mux_child_bus *cb = bus->priv;
> +	struct mdio_mux_parent_bus *pb = cb->parent;
> +	int r;
> +
> +	mutex_lock_nested(&pb->mii_bus->mdio_lock, MDIO_MUTEX_MUX);
> +	r = pb->switch_fn(pb->current_child, cb->bus_number, pb->switch_data);
> +	if (r)
> +		goto out;
> +
> +	pb->current_child = cb->bus_number;
> +
> +	r = pb->mii_bus->read_c45(pb->mii_bus, phy_id, dev_addr, regnum);

What if the parent bus doesn't have read_c45 or write_c45 ?

> @@ -173,6 +216,8 @@ int mdio_mux_init(struct device *dev,
>  		cb->mii_bus->parent = dev;
>  		cb->mii_bus->read = mdio_mux_read;
>  		cb->mii_bus->write = mdio_mux_write;
> +		cb->mii_bus->read_c45 = mdio_mux_read_c45;
> +		cb->mii_bus->write_c45 = mdio_mux_write_c45;

Maybe make these conditional on the parent bus implementing the c45
read/write ops?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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