Re: [RFC net-next 2/3] net: dsa: qca8k: enable assisted learning on CPU port

[DENG Qingfang <dqfext@gmail.com>]

On Sun, Aug 08, 2021 at 01:25:55AM +0300, Vladimir Oltean wrote:
> On Sat, Aug 07, 2021 at 08:07:25PM +0800, DENG Qingfang wrote:
> > Enable assisted learning on CPU port to fix roaming issues.
> 
> 'roaming issues' implies to me it suffered from blindness to MAC
> addresses learned on foreign interfaces, which appears to not be true
> since your previous patch removes hardware learning on the CPU port
> (=> hardware learning on the CPU port was supported, so there were no
> roaming issues)

The datasheet says learning is enabled by default, but if that's true,
the driver won't have to enable it manually.

Others have reported roaming issues as well:
https://github.com/Ansuel/openwrt/pull/3

As I don't have the hardware to test, I don't know what the default
value really is, so I just disable learning to make sure.

> 
> > 
> > Although hardware learning is available, it won't work well with
> > software bridging fallback or multiple CPU ports.
> 
> This part is potentially true however, but it would need proof. I am not
> familiar enough with the qca8k driver to say for sure that it suffers
> from the typical problem with bridging with software LAG uppers (no FDB
> isolation for standalone ports => attempt to shortcircuit the forwarding
> through the CPU port and go directly towards the bridged port, which
> would result in drops), and I also can't say anything about its support
> for multiple CPU ports.

QCA8337 supports disabling learning and FDB lookup on a per-VLAN basis,
so we could assign all standalone ports to a reserved VLAN (ID 0 or 4095)
with learning and FDB lookup disabled.

Ansuel has a patch set for multiple CPU ports.