netdev - Re: [DSA] fallback PTP to master port when switch does not support it

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Wed, 25 May 2022 17:00:24 +0200
From:   Rodolfo Giometti <giometti@...eenne.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Matej Zachar <zachar.matej@...il.com>, netdev@...r.kernel.org
Subject: Re: [DSA] fallback PTP to master port when switch does not support it

On 07/04/22 11:44, Vladimir Oltean wrote:
> On Tue, Apr 05, 2022 at 12:48:51PM -0700, Jakub Kicinski wrote:
>> On Tue, 5 Apr 2022 00:04:30 +0200 Andrew Lunn wrote:
>>> What i don't like about your proposed fallback is that it gives the
>>> impression the slave ports actually support PTP, when they do not.
>>
>> +1, running PTP on the master means there is a non-PTP-aware switch
>> in the path, which should not be taken lightly.
> 
> +2, the change could probably be technically done, and there are aspects
> worth discussing, but the goal presented here is questionable and it's
> best to not fool ourselves into thinking that the variable queuing delays
> of the switch are taken into account when reporting the timestamps,
> which they aren't.
> 
> I think that by the time you realize that you need PTP hardware
> timestamping on switch ports but you have a PTP-unaware switch
> integrated *into* your system, you need to go back to the drawing board.

IMHO this patch is a great hack but what you say sounds good to me.

However we can modify the patch in order to leave the default behavior as-is but 
adding the ability to enable this hack via DTS flag as follow:

                 ports {
                         #address-cells = <1>;
                         #size-cells = <0>;

                         port@0 {
                                 reg = <0>;
                                 label = "lan1";
                                 allow-ptp-fallback;
                         };

                         port@1 {
                                 reg = <1>;
                                 label = "lan2";
                         };

                         ...

                         port@5 {
                                 reg = <5>;
                                 label = "cpu";
                                 ethernet = <&fec>;

                                 fixed-link {
                                         speed = <1000>;
                                         full-duplex;
                                 };
                         };
                 };

Then the code can do as follow:

static int dsa_slave_ioctl(struct net_device *dev, struct ifreq *ifr, int cmd)
{
         struct dsa_slave_priv *p = netdev_priv(dev);
         struct dsa_switch *ds = p->dp->ds;
         int port = p->dp->index;
         struct net_device *master = dsa_slave_to_master(dev);

         /* Pass through to switch driver if it supports timestamping */
         switch (cmd) {
         case SIOCGHWTSTAMP:
                 if (ds->ops->port_hwtstamp_get)
                         return ds->ops->port_hwtstamp_get(ds, port, ifr);
                 if (p->dp->allow_ptp_fallback && master->netdev_ops->ndo_do_ioctl)
                         return master->netdev_ops->ndo_do_ioctl(master, ifr, cmd);
                 break;
         case SIOCSHWTSTAMP:
                 if (ds->ops->port_hwtstamp_set)
                         return ds->ops->port_hwtstamp_set(ds, port, ifr);
                 if (p->dp->allow_ptp_fallback && master->netdev_ops->ndo_do_ioctl)
                         return master->netdev_ops->ndo_do_ioctl(master, ifr, cmd);
                 break;
         }

         return phylink_mii_ioctl(p->dp->pl, ifr, cmd);
}

In this manner the default behavior is to return error if the switch doesn't 
support the PTP functions, but developers can intentionally enable the PTP 
fallback on specific ports only in order to be able to use PTP on buggy hardware.

Can this solution be acceptable?

Ciao,

Rodolfo

-- 
GNU/Linux Solutions                  e-mail: giometti@...eenne.com
Linux Device Driver                          giometti@...ux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti