Subject: Re: [PATCH net-next 3/5] net: sfp: configure/destroy I2C mdiobus on transceiver plug/unplug

From: Russell King - ARM Linux admin <[email-masked]>
Date: Thu, 29 Oct 2020 13:21:00 +0000

On Wed, Oct 28, 2020 at 11:14:25PM +0100, Marek Behún wrote:
> Instead of configuring the I2C mdiobus when SFP driver is probed,
> configure/destroy the mdiobus when SFP transceiver is plugged/unplugged.
> 
> This way we can tell the mdio-i2c code which protocol to use for each
> SFP transceiver.
> 
> Signed-off-by: Marek Behún <[email-masked]>
> Cc: Andrew Lunn <[email-masked]>
> Cc: Russell King <[email-masked]>
> ---
>  drivers/net/phy/sfp.c | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
> index b1f9fc3a5584..a392d5fc6ab4 100644
> --- a/drivers/net/phy/sfp.c
> +++ b/drivers/net/phy/sfp.c
> @@ -399,9 +399,6 @@ static int sfp_i2c_write(struct sfp *sfp, bool a2, u8 dev_addr, void *buf,
>  
>  static int sfp_i2c_configure(struct sfp *sfp, struct i2c_adapter *i2c)
>  {
> -	struct mii_bus *i2c_mii;
> -	int ret;
> -
>  	if (!i2c_check_functionality(i2c, I2C_FUNC_I2C))
>  		return -EINVAL;
>  
> @@ -409,7 +406,15 @@ static int sfp_i2c_configure(struct sfp *sfp, struct i2c_adapter *i2c)
>  	sfp->read = sfp_i2c_read;
>  	sfp->write = sfp_i2c_write;
>  
> -	i2c_mii = mdio_i2c_alloc(sfp->dev, i2c, MDIO_I2C_DEFAULT);
> +	return 0;
> +}
> +
> +static int sfp_i2c_mdiobus_configure(struct sfp *sfp, enum mdio_i2c_type type)
> +{
> +	struct mii_bus *i2c_mii;
> +	int ret;
> +
> +	i2c_mii = mdio_i2c_alloc(sfp->dev, sfp->i2c, type);
>  	if (IS_ERR(i2c_mii))
>  		return PTR_ERR(i2c_mii);
>  
> @@ -427,6 +432,12 @@ static int sfp_i2c_configure(struct sfp *sfp, struct i2c_adapter *i2c)
>  	return 0;
>  }
>  
> +static void sfp_i2c_mdiobus_destroy(struct sfp *sfp)
> +{
> +	mdiobus_unregister(sfp->i2c_mii);
> +	sfp->i2c_mii = NULL;
> +}
> +
>  /* Interface */
>  static int sfp_read(struct sfp *sfp, bool a2, u8 addr, void *buf, size_t len)
>  {
> @@ -1768,6 +1779,11 @@ static int sfp_sm_mod_probe(struct sfp *sfp, bool report)
>  	else
>  		sfp->module_t_start_up = T_START_UP;
>  
> +	/* Configure mdiobus */
> +	ret = sfp_i2c_mdiobus_configure(sfp, MDIO_I2C_DEFAULT);
> +	if (ret < 0)
> +		return ret;
> +

	return sfp_i2c_mdiobus_configure(sfp, MDIO_I2C_DEFAULT);

would be a simpler way to write this. However, I suggest handling this
elsewhere due to the point below.

> @@ -1778,6 +1794,8 @@ static void sfp_sm_mod_remove(struct sfp *sfp)
>  
>  	sfp_hwmon_remove(sfp);
>  
> +	sfp_i2c_mdiobus_destroy(sfp);
> +

This doesn't seem like the right place to handle this. This is called
from the module state machine (sfp_sm_module()) which is run before the
main state machine (sfp_sm_main()). The PHY is unregistered in the main
state machine, which means you're destroying the MII bus before the
PHY.

I guess what saves us from crashing is the refcounting, but this
doesn't seem to me to be particularly good.

Maybe create the MII bus after the "init_done" label, and destroy it
after we've called sfp_sm_phy_detach() ?

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