netdev - Re: [PATCH net] net: dsa: make dsa_master_ioctl() see through port_hwtstamp

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Date:   Fri, 11 Nov 2022 21:13:12 -0300
From:   Fabio Estevam <festevam@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Richard Cochran <richardcochran@...il.com>,
        Steffen Bätz <steffen@...osonix.de>
Subject: Re: [PATCH net] net: dsa: make dsa_master_ioctl() see through
 port_hwtstamp_get() shims

Hi Vladimir,

On Fri, Nov 11, 2022 at 6:10 PM Vladimir Oltean <vladimir.oltean@....com> wrote:
>
> There are multi-generational drivers like mv88e6xxx which have code like
> this:
>
> int mv88e6xxx_port_hwtstamp_get(struct dsa_switch *ds, int port,
>                                 struct ifreq *ifr)
> {
>         if (!chip->info->ptp_support)
>                 return -EOPNOTSUPP;
>
>         ...
> }
>
> DSA wants to deny PTP timestamping on the master if the switch supports
> timestamping too. However it currently relies on the presence of the
> port_hwtstamp_get() callback to determine PTP capability, and this
> clearly does not work in that case (method is present but returns
> -EOPNOTSUPP).
>
> We should not deny PTP on the DSA master for those switches which truly
> do not support hardware timestamping.
>
> Create a dsa_port_supports_hwtstamp() method which actually probes for
> support by calling port_hwtstamp_get() and seeing whether that returned
> -EOPNOTSUPP or not.
>
> Fixes: f685e609a301 ("net: dsa: Deny PTP on master if switch supports it")
> Link: https://patchwork.kernel.org/project/netdevbpf/patch/20221110124345.3901389-1-festevam@gmail.com/
> Reported-by: Fabio Estevam <festevam@...il.com>
> Reported-by: Steffen Bätz <steffen@...osonix.de>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Thanks for your fix!

Tested-by: Fabio Estevam <festevam@...x.de>