netdev - Re: dsa: sja1105: regression after patch: "net: dsa: configure the MTU for switch ports"

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Date:   Tue, 21 Apr 2020 14:58:28 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     mkl@...gutronix.de, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>, kernel@...gutronix.de,
        netdev <netdev@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        David Jander <david@...tonic.nl>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: dsa: sja1105: regression after patch: "net: dsa: configure the
 MTU for switch ports"

On Tue, Apr 21, 2020 at 02:56:37PM +0300, Vladimir Oltean wrote:
> Hi Oleksij,
> 
> On Tue, 21 Apr 2020 at 14:33, Oleksij Rempel <o.rempel@...gutronix.de> wrote:
> >
> > Hi Vladimir,
> >
> > I have a regression after this patch:
> > |commit bfcb813203e619a8960a819bf533ad2a108d8105
> > |Author:     Vladimir Oltean <vladimir.oltean@....com>
> > |
> > |  net: dsa: configure the MTU for switch ports
> >
> > with following log:
> > [    3.044065] sja1105 spi1.0: Probed switch chip: SJA1105Q
> > [    3.071385] sja1105 spi1.0: Enabled switch tagging
> > [    3.076484] sja1105 spi1.0: error -34 setting MTU on port 0
> > [    3.082795] sja1105: probe of spi1.0 failed with error -34
> >
> > this is devicetree snippet for the port 0:
> >         port@0 {
> >                 reg = <0>;
> >                 label = "usb";
> >                 phy-handle = <&usbeth_phy>;
> >                 phy-mode = "rmii";
> >         };
> >
> >
> > Is it know issue?
> >
 
> The code which is causing problems seems to be this one:
> 
>     mtu_limit = min_t(int, master->max_mtu, dev->max_mtu);
>     old_master_mtu = master->mtu;
>     new_master_mtu = largest_mtu + cpu_dp->tag_ops->overhead;
>     if (new_master_mtu > mtu_limit)
>         return -ERANGE;
> 
> called from
> 
>     rtnl_lock();
>     ret = dsa_slave_change_mtu(slave_dev, ETH_DATA_LEN);
>     rtnl_unlock();
>     if (ret && ret != -EOPNOTSUPP) {
>         dev_err(ds->dev, "error %d setting MTU on port %d\n",
>             ret, port->index);
>         goto out_free;
>     }
> 
> Before this patch, it was silently failing, now it's preventing the
> probing of the ports which I might agree with you is not better.
> Andrew warned about this, and I guess that during probe, we should
> warn but ignore any nonzero return code, not just EOPNOTSUPP. I'll
> send a patch out shortly to correct this.
> 
> Out of curiosity, what DSA master port do you have? Does it not
> support an MTU of 1504 bytes? Does MTU-sized traffic pass correctly
> through your interface? (you can test with iperf3)

It is FEC@...6QP attached to the port 4 of the sja1105 switch.
I'll try to make some tests tomorrow.

Regards,
Oleksij
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