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Date: Tue, 20 Mar 2018 13:09:36 +0100
From: Andrew Lunn <andrew@lunn.ch>
To: Frantisek Rysanek <Frantisek.Rysanek@post.cz>
Cc: netdev@vger.kernel.org
Subject: Re: HW question: i210 vs. BCM5461S over SGMII: no response from PHY
 to MDIO requests?
Message-ID: <20180320120936.GA19142@lunn.ch>
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> i2cdetect has found three i2c slaves (identical layout in both SFP's) 
> at addresses 0x50, 0x51 and 0x56.
> What are they? EEPROM, DDM and "MDIO over i2c" ?
> The SFP's likely lack a proper SFP MSA data structure.

0x50 and 0x51 are EEPROM like. See drivers/net/phy/sfp.c. The standard
at24 EEPROM driver can also read it. And so should the SFP code in the
igb driver!

> Does this make sense as some sort of proprietary standard 
> (Cisco, if I should take the vendor's label at face value),
> or is this likely some "3rd-party innovation thinko", not worth
> implementing?

See if drivers/net/phy/mdio-i2c.c is useful. I'm just guessing here.

    Andrew