netdev - Re: [PATCH net-next v2 07/10] net: dsa: lan9303: Added basic offloading of unicast traffic

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Message-ID: <20170727133113.GB18666@lunn.ch>
Date:   Thu, 27 Jul 2017 15:31:13 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Egil Hjelmeland <privat@...l-hjelmeland.no>
Cc:     corbet@....net, vivien.didelot@...oirfairelinux.com,
        f.fainelli@...il.com, davem@...emloft.net, kernel@...gutronix.de,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2 07/10] net: dsa: lan9303: Added basic
 offloading of unicast traffic

> >I think you are over-simplifying here. Say i have a layer 2 VPN and i
> >bridge port 1 and the VPN? The software bridge still wants to do STP
> >on port 1, in order to solve loops.
> >
> 
> Problem is that the mainline lan9303_separate_ports() does its
> work by setting port 1 & 2 in STP BLOCKING state (and port 0 in
> FORWARDING state). So my understanding is that it would break port
> separation if LAN9303_SWE_PORT_STATE is written while the driver
> is in the non-bridged state.

If the hardware cannot do it, that is a different matter. But if the
hardware can do STP states per port, you should try to make use of it
here.

> I thought the SW bridge would carry doing its STP work even if
> there is a port_stp_state_set method on a DSA port?

It will, but it means you are dropping frames in software, adding
extra load to the CPU, reducing the available bandwidth for the other
port, etc.

       Andrew