[RFC PATCH net 5/5] net: dsa: xrs700x: be compatible with masters which unregister on shutdown

[George McCollister]

On Sun, Sep 12, 2021 at 7:09 AM Vladimir Oltean <vladimir.oltean at nxp.com> wrote:
>
> Since commit 2f1e8ea726e9 ("net: dsa: link interfaces with the DSA
> master to get rid of lockdep warnings"), DSA gained a requirement which
> it did not fulfill, which is to unlink itself from the DSA master at
> shutdown time.
>
> Since the Arrow SpeedChips XRS700x driver was introduced after the bad
> commit, it has never worked with DSA masters which decide to unregister
> their net_device on shutdown, effectively hanging the reboot process.
> To fix that, we need to call dsa_switch_shutdown.
>
> These devices can be connected by I2C or by MDIO, and if I search for
> I2C or MDIO bus drivers that implement their ->shutdown by redirecting
> it to ->remove I don't see any, however this does not mean it would not
> be possible. To be compatible with that pattern, it is necessary to
> implement an "if this then not that" scheme, to avoid ->remove and
> ->shutdown from being called both for the same struct device.
>
> Fixes: ee00b24f32eb ("net: dsa: add Arrow SpeedChips XRS700x driver")
> Link: https://lore.kernel.org/netdev/20210909095324.12978-1-LinoSanfilippo@gmx.de/
> Reported-by: Lino Sanfilippo <LinoSanfilippo at gmx.de>
> Signed-off-by: Vladimir Oltean <vladimir.oltean at nxp.com>
> ---
>  drivers/net/dsa/xrs700x/xrs700x.c      |  6 ++++++
>  drivers/net/dsa/xrs700x/xrs700x.h      |  1 +
>  drivers/net/dsa/xrs700x/xrs700x_i2c.c  | 18 ++++++++++++++++++
>  drivers/net/dsa/xrs700x/xrs700x_mdio.c | 18 ++++++++++++++++++
>  4 files changed, 43 insertions(+)
>
> diff --git a/drivers/net/dsa/xrs700x/xrs700x.c b/drivers/net/dsa/xrs700x/xrs700x.c
> index 130abb0f1438..469420941054 100644
> --- a/drivers/net/dsa/xrs700x/xrs700x.c
> +++ b/drivers/net/dsa/xrs700x/xrs700x.c
> @@ -822,6 +822,12 @@ void xrs700x_switch_remove(struct xrs700x *priv)
>  }
>  EXPORT_SYMBOL(xrs700x_switch_remove);
>
> +void xrs700x_switch_shutdown(struct xrs700x *priv)
> +{
> +       dsa_switch_shutdown(priv->ds);
> +}
> +EXPORT_SYMBOL(xrs700x_switch_shutdown);
> +
>  MODULE_AUTHOR("George McCollister <george.mccollister at gmail.com>");
>  MODULE_DESCRIPTION("Arrow SpeedChips XRS700x DSA driver");
>  MODULE_LICENSE("GPL v2");
> diff --git a/drivers/net/dsa/xrs700x/xrs700x.h b/drivers/net/dsa/xrs700x/xrs700x.h
> index ff62cf61b091..4d58257471d2 100644
> --- a/drivers/net/dsa/xrs700x/xrs700x.h
> +++ b/drivers/net/dsa/xrs700x/xrs700x.h
> @@ -40,3 +40,4 @@ struct xrs700x {
>  struct xrs700x *xrs700x_switch_alloc(struct device *base, void *devpriv);
>  int xrs700x_switch_register(struct xrs700x *priv);
>  void xrs700x_switch_remove(struct xrs700x *priv);
> +void xrs700x_switch_shutdown(struct xrs700x *priv);
> diff --git a/drivers/net/dsa/xrs700x/xrs700x_i2c.c b/drivers/net/dsa/xrs700x/xrs700x_i2c.c
> index 489d9385b4f0..6deae388a0d6 100644
> --- a/drivers/net/dsa/xrs700x/xrs700x_i2c.c
> +++ b/drivers/net/dsa/xrs700x/xrs700x_i2c.c
> @@ -109,11 +109,28 @@ static int xrs700x_i2c_remove(struct i2c_client *i2c)
>  {
>         struct xrs700x *priv = i2c_get_clientdata(i2c);
>
> +       if (!priv)
> +               return 0;
> +
>         xrs700x_switch_remove(priv);
>
> +       i2c_set_clientdata(i2c, NULL);
> +
>         return 0;
>  }
>
> +static void xrs700x_i2c_shutdown(struct i2c_client *i2c)
> +{
> +       struct xrs700x *priv = i2c_get_clientdata(i2c);
> +
> +       if (!priv)
> +               return;
> +
> +       xrs700x_switch_shutdown(priv);
> +
> +       i2c_set_clientdata(i2c, NULL);
> +}
> +
>  static const struct i2c_device_id xrs700x_i2c_id[] = {
>         { "xrs700x-switch", 0 },
>         {},
> @@ -137,6 +154,7 @@ static struct i2c_driver xrs700x_i2c_driver = {
>         },
>         .probe  = xrs700x_i2c_probe,
>         .remove = xrs700x_i2c_remove,
> +       .shutdown = xrs700x_i2c_shutdown,
>         .id_table = xrs700x_i2c_id,
>  };
>
> diff --git a/drivers/net/dsa/xrs700x/xrs700x_mdio.c b/drivers/net/dsa/xrs700x/xrs700x_mdio.c
> index 44f58bee04a4..d01cf1073d49 100644
> --- a/drivers/net/dsa/xrs700x/xrs700x_mdio.c
> +++ b/drivers/net/dsa/xrs700x/xrs700x_mdio.c
> @@ -136,7 +136,24 @@ static void xrs700x_mdio_remove(struct mdio_device *mdiodev)
>  {
>         struct xrs700x *priv = dev_get_drvdata(&mdiodev->dev);
>
> +       if (!priv)
> +               return;
> +
>         xrs700x_switch_remove(priv);
> +
> +       dev_set_drvdata(&mdiodev->dev, NULL);
> +}
> +
> +static void xrs700x_mdio_shutdown(struct mdio_device *mdiodev)
> +{
> +       struct xrs700x *priv = dev_get_drvdata(&mdiodev->dev);
> +
> +       if (!priv)
> +               return;
> +
> +       xrs700x_switch_shutdown(priv);
> +
> +       dev_set_drvdata(&mdiodev->dev, NULL);
>  }
>
>  static const struct of_device_id __maybe_unused xrs700x_mdio_dt_ids[] = {
> @@ -155,6 +172,7 @@ static struct mdio_driver xrs700x_mdio_driver = {
>         },
>         .probe  = xrs700x_mdio_probe,
>         .remove = xrs700x_mdio_remove,
> +       .shutdown = xrs700x_mdio_shutdown,
>  };
>
>  mdio_module_driver(xrs700x_mdio_driver);
> --
> 2.25.1
>

Looks good to me.
Assuming we do Reviewed-by for RFCs:
Reviewed-by: George McCollister <george.mccollister at gmail.com>