netdev - Re: [PATCH net] net: dsa: Don't instantiate phylink for CPU/DSA ports unless needed

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Date:   Thu, 12 Mar 2020 02:24:08 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Russell King <rmk+kernel@....linux.org.uk>,
        Ioana Ciornei <ioana.ciornei@....com>
Subject: Re: [PATCH net] net: dsa: Don't instantiate phylink for CPU/DSA ports
 unless needed

On Wed, 11 Mar 2020 at 17:24, Andrew Lunn <andrew@...n.ch> wrote:
>
> By default, DSA drivers should configure CPU and DSA ports to their
> maximum speed. In many configurations this is sufficient to make the
> link work.
>
> In some cases it is necessary to configure the link to run slower,
> e.g. because of limitations of the SoC it is connected to. Or back to
> back PHYs are used and the PHY needs to be driven in order to
> establish link. In this case, phylink is used.
>
> Only instantiate phylink if it is required. If there is no PHY, or no
> fixed link properties, phylink can upset a link which works in the
> default configuration.
>
> Fixes: 0e27921816ad ("net: dsa: Use PHYLINK for the CPU/DSA ports")
> Signed-off-by: Andrew Lunn <andrew@...n.ch>
> ---


No regressions on ocelot/felix and sja1105, which have no .adjust_link
and do have fixed-link for the CPU port.

>  net/dsa/port.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/net/dsa/port.c b/net/dsa/port.c
> index ed7dabb57985..ec13dc666788 100644
> --- a/net/dsa/port.c
> +++ b/net/dsa/port.c
> @@ -648,9 +648,14 @@ static int dsa_port_phylink_register(struct dsa_port *dp)
>  int dsa_port_link_register_of(struct dsa_port *dp)
>  {
>         struct dsa_switch *ds = dp->ds;
> +       struct device_node *phy_np;
>
> -       if (!ds->ops->adjust_link)
> -               return dsa_port_phylink_register(dp);
> +       if (!ds->ops->adjust_link) {
> +               phy_np = of_parse_phandle(dp->dn, "phy-handle", 0);
> +               if (of_phy_is_fixed_link(dp->dn) || phy_np)
> +                       return dsa_port_phylink_register(dp);
> +               return 0;
> +       }
>
>         dev_warn(ds->dev,
>                  "Using legacy PHYLIB callbacks. Please migrate to PHYLINK!\n");
> @@ -665,11 +670,12 @@ void dsa_port_link_unregister_of(struct dsa_port *dp)
>  {
>         struct dsa_switch *ds = dp->ds;
>
> -       if (!ds->ops->adjust_link) {
> +       if (!ds->ops->adjust_link && dp->pl) {
>                 rtnl_lock();
>                 phylink_disconnect_phy(dp->pl);
>                 rtnl_unlock();
>                 phylink_destroy(dp->pl);
> +               dp->pl = NULL;
>                 return;
>         }
>
> --
> 2.25.1
>

Thanks,
-Vladimir