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From:   Ioana Ciornei <ioana.ciornei@nxp.com>
To:     Andrew Lunn <andrew@lunn.ch>
CC:     "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "f.fainelli@gmail.com" <f.fainelli@gmail.com>
Subject: RE: [PATCH 06/12] staging: dpaa2-ethsw: add ACL entry to redirect STP
 to CPU
Thread-Topic: [PATCH 06/12] staging: dpaa2-ethsw: add ACL entry to redirect
 STP to CPU
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Date:   Wed, 6 Nov 2019 13:47:47 +0000
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> Subject: Re: [PATCH 06/12] staging: dpaa2-ethsw: add ACL entry to redirec=
t
> STP to CPU
>=20
> > The control queues do not form an actual interface in the sense that
> > the CPU does not receive unknown unicast, broadcast and multicast
> > frames by default.  For each frame that we want to direct to the CPU
> > we must add an ACL entry.
>=20
> So this appears to be one of the dumbest switches so far :-(

To be fair, the actual hardware can do much more.
The problem here is that the firmware models the switch in a non-Linux styl=
e.

>=20
> Can you add an ACL which is all L2 broadcast/multicast?  That would be a =
good
> first step.

I can add that but it would not be enough.
For example, unknown unicast would not be matched thus would not reach the =
CPU.

>=20
> Does the ACL stop further processing of the frame? Ideally you want the
> switch to also flood broadcast/multicast out other ports, if they are in =
a
> bridge. If it cannot, you end up with the software bridge doing the flood=
ing.

Yes, the ACL stops any further processing.=20

>=20
> So i also assume it does not perform learning on CPU frames? That probabl=
y
> means you need to connect up the fdb add/remove calls to add in ACLs. And
> you will need to implement ndo_set_rx_mode. Each unicast and multicast
> address needs to be turned into an ACL. What i don't know is if the netwo=
rk
> stack will automatically add the interfaces own MAC address. You might ha=
ve
> to handle that special case.
>=20
>     Andrew

Your assumption is true, learning, with the current implementation, is not =
possible for CPU frames.
In .ndo_start_xmit() we inject directly into the switch port's Tx queues, t=
hus bypassing the entire learning process.

All in all, I do not see a way out just by using the ACL mechanism (because=
 of unknown unicast frames).

I have to talk in detail with the firmware team, but from what I can unders=
tand if we make the following changes in firmware it would better fit the L=
inux framework:
 * make the CPU receive unknown unicast, broadcast and multicast frames by =
default (without any ACLs)
 * frames originated on the CPU should not bypass the learning process (it =
should have its own Tx queues that go through the same learning process)

Thanks,
Ioana