netdev - Re: Quirks for exotic SFP module

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Message-Id: <75Q7UR.PII4PI72J55K3@brun.one>
Date: Sat, 06 May 2023 03:15:07 +0200
From: Lorenz Brun <lorenz@...n.one>
To: Andrew Lunn <andrew@...n.ch>
Cc: netdev@...r.kernel.org, Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: Quirks for exotic SFP module

Am Sa, 6. Mai 2023 um 03:05:10 +02:00:00 schrieb Andrew Lunn 
<andrew@...n.ch>:
>>  I tested and I got a bunch of addresses showing up on i2c master 
>> connected
>>  to the module. 1b, 30, 31, 34, 35, 36, 50 and 53. But I'm still not 
>> sure why
>>  we'd want to talk MDIO with this module. AFAIK MDIO is an Ethernet 
>> thing,
>>  the module is talking G.fast to the outside which is a completely 
>> different
>>  protocol from a completely different family of protocols. It has 
>> its own
>>  management protocol which runs over Ethernet.
> 
> One reason you might want to talk to the PHY is to correct is
> configuration. 1000Base-X includes inband signalling. There are some
> Copper SFP which have the inband signalling disabled. And that can
> make the host unhappy, it fails to link up. It varies from host to
> host. Some work, some don't.

Oh, so you're talking about signalling on the AR8033 <-> Linux Host 
part of the link. I actually wasn't aware that 1000Base-X did in-band 
signalling, TIL. Since the I2C bus is connected to the modem SoC it 
would have to forward any MDIO to the AR8033 transceiver, right? This 
would also be a bit weird as the AR8033 is connected "backwards", i.e. 
with RGMII facing towards the Modem SoC and 1000Base-X towards the 
Linux host.

Regards,
Lorenz