netdev - Re: Is it currently possible to connect SFP to dsa port?

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Date:   Wed, 8 Aug 2018 15:52:19 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Marek Behún <marek.behun@....cz>
Cc:     netdev@...r.kernel.org,
        Russell King - ARM Linux <linux@...linux.org.uk>
Subject: Re: Is it currently possible to connect SFP to dsa port?

> Let me know when you have the first version ready, I will try it. Our
> router can connect SFP board directly to the CPU board, or there may up
> to three mv88e6190 switch boards between SFP board and cpu board.

So you are using D in DSA? The board i'm using has two SFF modules,
both on the second switch in the chain. But D in DSA makes no
difference to SFPs.

> Do you already have a stable dts binding for how to bind sfp to dsa
> port?

Nothing special is needed. It just follows the standard SFP binding
for a MAC port. The DT changes for the board i'm using will be part of
the patchset i send.

> The mv88e6190/6390 can configure ports 9 and 10 to either
> 1000BASE-X/SGMII od 2500BASE-X, but this has to be done by setting a
> pin and reseting the switch.

I've been using 6390X, not 6390. The cmode nibble is writable for
ports 9 and 10. So you can change between 1000BASE-X, SGMII and
2500BASE-X by writing to the cmode. I assume 6390 is the same. As
Russell pointed out, you need this dynamic behaviour, since SFP
modules are hot pluggable, and you need to configure the mode
depending on what the module is. Also, what the peer is can also make
a difference. The board i have, the MAC/SFF combination can do
2500Base-X, by my peer cannot. Phylink defaults to 2500Base-X, so i
need to use ethtool to force it to 1000Base-X in order to get a link
with the peer.

     Andrew