Aw: Re: [PATCH v2] net: ethernet: mtk_eth_soc: fix mtu warning

[Frank Wunderlich]

> Gesendet: Donnerstag, 09. Juli 2020 um 15:41 Uhr
> Von: "Andrew Lunn" <andrew at lunn.ch>

> > +	eth->netdev[id]->max_mtu = 1536;
>
> I assume this is enough to make the DSA warning go away, but it is the
> true max? I have a similar patch for the FEC driver which i should
> post sometime. Reviewing the FEC code and after some testing, i found
> the real max was 2K - 64.

i tried setting only the max_mtu, but the dsa-error is still present

mt7530 mdio-bus:00: nonfatal error -95 setting MTU on port 0

but i got it too, if i revert the change...mhm, strange that these were absent last time...

the other 2 are fixed with only max_mtu.
@andrew where did you got the 2k-64 (=1984) information? sounds like orwell ;)

-95 is EOPNOTSUPP

as so far, commit 72579e14a1d3d3d561039dfe7e5f47aaf22e3fd3 introduces the warning,
but the change is making it non-fatal...so i need to adjust my fixes-tag.
i guess the real problem lies in this:

bfcb813203e6 net: dsa: configure the MTU for switch ports

it looks like dsa_slave_change_mtu failes because of missing callback in mtk_driver (mt7530 for mt7531 in my case).

net/dsa/slave.c
1405 static int dsa_slave_change_mtu(struct net_device *dev, int new_mtu)
...
1420     if (!ds->ops->port_change_mtu)
1421         return -EOPNOTSUPP;

i added an empty callback to avoid this message, but mtu should be set in hardware too...
here i will ne some assistance from mtk ethernet experts and mt7531 driver (from landen chao) to be merged first (after some needed changes)

--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -2259,6 +2259,12 @@ mt753x_phy_write(struct dsa_switch *ds, int port, int regnum, u16 val)
        return priv->info->phy_write(ds, port, regnum, val);
 }

+static int
+mt753x_port_change_mtu(struct dsa_switch *ds, int port, int new_mtu)
+{
+       return 0;
+}
+
 static const struct dsa_switch_ops mt7530_switch_ops = {
        .get_tag_protocol       = mtk_get_tag_protocol,
        .setup                  = mt753x_setup,
@@ -2281,6 +2287,7 @@ static const struct dsa_switch_ops mt7530_switch_ops = {
        .port_vlan_del          = mt7530_port_vlan_del,
        .port_mirror_add        = mt7530_port_mirror_add,
        .port_mirror_del        = mt7530_port_mirror_del,
+       .port_change_mtu        = mt753x_port_change_mtu,
        .phylink_validate       = mt753x_phylink_validate,
        .phylink_mac_link_state = mt7530_phylink_mac_link_state,
        .phylink_mac_config     = mt753x_phylink_mac_config,