Re: [PATCH] net: dsa: qca8k: Disable mgmt Ethernet for qca8327

[Michał Kępień]

Andrew,

First of all, after taking a closer look at this issue and the driver
code, I realized that the approach I went with in the patch stemmed from
my ignorance and that I submitted it too quickly - apologies about that.

> > While the qca8327 switch appears to support in-band mgmt Ethernet,
> > prolonged use of that protocol (e.g. for polling link state) makes the
> > device unstable: within minutes, ports randomly go down and no traffic
> > is forwarded anymore.  The same issues do not occur when MDIO is used
> > exclusively, so ensure mgmt Ethernet is not used on the qca8327.
> 
> Do you have time to narrow down the cause?

Sure, I should be able to spare a few cycles on this in the upcoming
weeks.

> I _think_ in band management is used for a few different
> things. e.g. statistics, as you said, PHY polling etc. Rather than
> turning everything off, could you try just doing PHY polling via MDIO,
> but statistics via ethernet, and do an ethtool -S every so often to
> see if you can trigger the problem.

Ack, I'll try that.

> Could you also check if the management packets are getting lost? Look
> at the results from wait_for_completion_timeout(), is it timing out?

Ack.

> If so, is the retry mechanism working? When i added the Marvell
> equivalent for in-band signalling i got the retry mechanism wrong, but
> never noticed because i was not loosing packets.

Could you please point me at the exact retry mechanism you had in mind,
either the qca8k one or the Marvell equivalent?  I cannot see any in
drivers/net/dsa/qca/qca8k-8xxx.c.  If I'm reading qca8k code correctly,
when wait_for_completion_timeout() fails, its return value is just
bubbled up the call chain.

Thanks,

-- 
Best regards,
Michał Kępień