Re: [RFC PATCH net-next 3/3] net: dsa: listen for SWITCHDEV_{FDB,DEL}_ADD_TO_DEVICE on foreign bridge neighbors

From: Florian Fainelli <f.fainelli@gmail.com>
To: Vladimir Oltean <olteanv@gmail.com>,
	Tobias Waldekranz <tobias@waldekranz.com>
Cc: Andrew Lunn <andrew@lunn.ch>, DENG Qingfang <dqfext@gmail.com>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Jakub Kicinski <kuba@kernel.org>, netdev <netdev@vger.kernel.org>,
	linux-kernel@vger.kernel.org, Marek Behun <marek.behun@nic.cz>,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>
Subject: Re: [RFC PATCH net-next 3/3] net: dsa: listen for SWITCHDEV_{FDB,DEL}_ADD_TO_DEVICE on foreign bridge neighbors
Date: Thu, 12 Nov 2020 19:48:36 -0800	[thread overview]
Message-ID: <6a86a756-51c8-51a1-b782-5dee7baf9b77@gmail.com> (raw)
In-Reply-To: <20201109123813.kjzvel7pszhcmcgw@skbuf>

On 11/9/2020 4:38 AM, Vladimir Oltean wrote:
> On Mon, Nov 09, 2020 at 02:31:11PM +0200, Vladimir Oltean wrote:
>> I need to sit on this for a while. How many DSA drivers do we have that
>> don't do SA learning in hardware for CPU-injected packets? ocelot/felix
>> and mv88e6xxx? Who else? Because if there aren't that many (or any at
>> all except for these two), then I could try to spend some time and see
>> how Felix behaves when I send FORWARD frames to it. Then we could go on
>> full blast with the other alternative, to force-enable address learning
>> from the CPU port, and declare this one as too complicated and not worth
>> the effort.
> 
> In fact I'm not sure that I should be expecting an answer to this
> question. We can evaluate the other alternative in parallel. Would you
> be so kind to send some sort of RFC for your TX-side offload_fwd_mark so
> that I could test with the hardware I have, and get a better understanding
> of the limitations there?

For Broadcom switches, ARL (Address Resolution Logic, where learning
happens) is bypassed when packets ingress the CPU port with opcode 1
which is what net/dsa/tag_brcm.c uses. When opcode 0 is used, address
learning occurs.

The reason why opcode 1 is used is because of the Advanced Congestion
Buffering (ACB) which requires us to steer packets towards a particular
switch port and egress queue number within that port. With opcode 0 we
would not be able to do that.

We could make the opcode dependent on the switch/DSA master since not
all combinations support ACB, but given we have 3 or 4 Ethernet switches
kind within DSA that do not do learning from the CPU port, I guess we
need a solution to that problem somehow.
-- 
Florian