Subject: Re: [RFC net-next 6/8] net: phylink: Configure MAC/PCS when link is up without PHY

From: Russell King - ARM Linux admin <[email-masked]>
Date: Mon, 27 Jan 2020 16:11:32 +0000

On Mon, Jan 27, 2020 at 03:51:07PM +0100, Andrew Lunn wrote:
> > Can you give a hint which platform this is and how to reproduce it
> > please?
> 
> Hi Russell
> 
> Devel C has issues with its fibre ports. I tend to test with
> sff2/port9 not sff3/port3, because i also have the copper port plugged
> in. If the copper gets link before the fibre, copper is used.
> 
> What i see is that after the SERDES syncs, its registers indicate a 1G
> link, full duplex, etc. But the MAC is using 10/Half. And hence no
> packets go through. If i set the MAC to the same as the PCS, i can at
> least transmit. Receive does not work, but i think that is something
> else. The statistics counters indicate the SERDES is receiving frames,
> but the MAC statistic counters suggests the MAC never sees them.
> 
> I've also had issues with the DSA links, also being configured to
> 10/Half. That seems to be related to having a phy-mode property in
> device tree. I need to add a fixed-link property to set the correct
> speed. Something is broken here, previously the fixed-link was only
> needed if the speed needed to be lower than the ports maximum. I think
> that is a separate issue i need to dig into, not part of the PCS to
> MAC transfer.

Presumably, all these should be visible on the ZII rev B as well?
I've not noticed any issues there, and I have 5.4 built from my
tree on December 22nd which would've included most of what is in
5.5, and quite a bit of what's queued in net-next.

There, I see:

mv88e6xxx.0/regs:    GLOBAL GLOBAL2 SERDES     0    1    2    3    4    5    6
mv88e6xxx.0/regs: 1:     2    8007     149     3    3    3    3    3 403e   3d
mv88e6xxx.1/regs:    GLOBAL GLOBAL2 SERDES     0    1    2    3    4    5    6
mv88e6xxx.1/regs: 1:     2    8807     14d     3    3    3    3    3 403e 403e
mv88e6xxx.2/regs:    GLOBAL GLOBAL2 SERDES     0    1    2    3    4    5    6    7    8    9
regs: 1:  7209       0    ffff  c503 c503 c503 2403 2403 2403 2403 2403 2403 c13e

which looks fine to me:
- switch 0
   - port 5 is the DSA port, which is forced to 1G.
   - port 6 is the CPU port, which is forced to 100M.
- switch 1
   - ports 5 and 6 are DSA ports, forced to 1G
- switch 2
   - port 9 is the DSA port, forced to 1G.

Booting 5.5 is more noisy than 5.4 - there's loads of complaints about
"already a member of VLAN 1".  As far as the port MAC settings go, it
looks just the same as the 5.4 settings I quoted above.

Now, I do have some differences between what is in mainline and my tree
and one of them involves adding a whole bunch of "phylink_mac_config"
and "phylink_link_force" methods to the mv88e6xxx_ops for Marvell DSA
switches.  Without these, dsa_port_phylink_mac_config() will ignore
phylink's attempts to configure the MAC.

Quite why this is, I don't know; these are patches I've carried for
ages, since trying to get the SFF modules working on these platforms,
before mainline gained phylink support for DSA.  I seem to remember
that mainline's work was based on what I'd done, or was very similar,
but I never really understood why bits such as this were left out.
Since this work has been published online in my git tree since day 1,
I find it really strange that people go off and do what seems to be a
half-hearted implementation.  See the "zii" branch.

Mainline did diverge on the issue of how the SFF modules should be
driven; whether to drive them with the SFP code or whether to use
a fixed-link instead.  I've kept my original approach, which is less
than perfect since we don't have a link interrupt to trigger the call
to phylink_mac_change().  However, I'm suspecting that once we solve
the PCS/MAC split issue, and use the clause 37 phylink PCS helpers
I've proposed in the last few weeks, this will be resolvable.

> Heiner has another device which has an Aquantia PHY running in an odd
> mode so that it does 1G over a T2 link. It uses SGMII for this, and
> that is where we first noticed the issue of the MAC and PCS having
> different configurations.

Do you know when the issue appeared?

It sounds like this regression has been known for some time, yet this
is the first I've heard about it.

-- 
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