netdev - Re: [RFC 3/9] net: dsa: mv88e6xxx: add support for VTU ops

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Message-ID: <20150603021714.GA932@roeck-us.net>
Date:	Tue, 2 Jun 2015 19:17:14 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Vivien Didelot <vivien.didelot@...oirfairelinux.com>
Cc:	netdev <netdev@...r.kernel.org>, David <davem@...emloft.net>,
	Florian Fainelli <f.fainelli@...il.com>,
	Andrew Lunn <andrew@...n.ch>,
	Scott Feldman <sfeldma@...il.com>,
	Jiri Pirko <jiri@...nulli.us>,
	Jérome Oufella 
	<jerome.oufella@...oirfairelinux.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	kernel <kernel@...oirfairelinux.com>,
	Chris Healy <cphealy@...il.com>
Subject: Re: [RFC 3/9] net: dsa: mv88e6xxx: add support for VTU ops

On Tue, Jun 02, 2015 at 09:39:50PM -0400, Vivien Didelot wrote:
> Guenter,
> 
> On Jun 2, 2015, at 2:50 AM, Guenter Roeck linux@...ck-us.net wrote:
> > On 06/01/2015 06:27 PM, Vivien Didelot wrote:
> >> +    /* Bringing an interface up adds it to the VLAN 0. Ignore this. */
> >> +    if (!vid)
> >> +        return 0;
> >> +
> > 
> > Me puzzled ;-). I brought this and the fid question up before.
> > No idea if my e-mail got lost or what happened.
> > 
> > Can you explain why we don't need a configuration for vlan 0 ?
> 
> Sorry for late reply. Initially, when issuing "ip link set up dev swp0",
> ndo_vlan_rx_add_vid was called to add the interface in the VLAN 0.
> 
Loading the 802.1q module has the same effect.

I think this may be on purpose; it is telling the switch to accept
packets with vid==0 (and untagged packets).

> 2 things happen here:
> 
>   * this is inconsistent with the "bridge vlan" output which doesn't seem to
>     know about a VID 0;
>   * VID 0 seems special for this switch: if an ingressing frame has VID 0, the
>     tagged port will override the VID bits with the port default VID at egress.
> 
As far as I can see, the switch treats packets with vid==0 and untaged packets
as unknown if VLAN support is enabled.

Anyway, sounds odd. Sure this isn't a configuration problem somethere ?

Thanks,
Guenter
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