netdev - Re: Using a bridge for DSA and non-DSA devices

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Message-ID: <20221205190805.vwcv6z7ize3z64j2@skbuf>
Date:   Mon, 5 Dec 2022 21:08:05 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Christian Eggers <ceggers@...i.de>
Cc:     netdev@...r.kernel.org
Subject: Re: Using a bridge for DSA and non-DSA devices

Hi Christian,

On Mon, Dec 05, 2022 at 07:15:42PM +0100, Christian Eggers wrote:
> Usually a bridge does forwarding of traffic between different hardware
> interfaces in software. For DSA, setting up a bridge configures the
> hardware in a way that traffic is forwarded in hardware.
> 
> Is there any problem combining these two situations on a single bridge?
> Currently I use a bridge for configuring a DSA switch with two DSA slave
> interfaces. Can I add a non-DSA device (e.g. an USB Ethernet gadget)
> to this bridge?

In the model that the DSA core tries to impose, software bridging is
possible, as long as you understand the physical constraints (throughput
will be limited by the link speed of the CPU ports), and as long as the
switch doesn't use DSA_TAG_PROTO_NONE (a remnant of the past).

Unfortunately the results might depend on which switch driver you use
for this, since some driver cooperation is needed for smooth sailing,
and we don't see perfect uniformity. See the
ds->assisted_learning_on_cpu_port flag for some more details.

Did you already try to experiment with software bridging and faced any
issues?