netdev - Re: [PATCH net-next 1/2] mlxsw: core: Add ethtool support for QSFP-DD transceivers

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Message-ID: <CAL_jBfT93picGGoCNWQDY21pWmo3jffanhBzqVwm1kVbyEb4ow@mail.gmail.com>
Date:   Fri, 26 Jun 2020 18:33:55 +0100
From:   Adrian Pop <popadrian1996@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Ido Schimmel <idosch@...sch.org>, netdev@...r.kernel.org,
        davem@...emloft.net, kuba@...nel.org, jiri@...lanox.com,
        vadimp@...lanox.com, mlxsw@...lanox.com,
        Ido Schimmel <idosch@...lanox.com>
Subject: Re: [PATCH net-next 1/2] mlxsw: core: Add ethtool support for QSFP-DD transceivers

>
> Is page 03h valid for a QSFP DD? Do we add pages 10h and 11h after
> page 03h, or instead of? How do we indicate to user space what pages
> of data have been passed to it?
>
>    Andrew

>From QSFP-DD CMIS Rev 4.0: "In particular, support of the Lower Memory
and of Page 00h is required for all modules, including passive copper
cables. These pages are therefore always implemented. Additional
support for Pages 01h, 02h and bank 0 of Pages 10h and 11h is required
for all paged memory modules."

According to the same document, page 0x03 contains "User EEPROM
(NVRs)". Byte 142, bit 2, page 0x01 indicates if the user page 0x03
was implemented. I did not find anything about page 0x02 (where the
user EEPROM is stored) in the documentation for QSFP. I suppose it is
always implemented? If we really want to have it so it is similar to
QSFP, one could send 896 bytes (instead of 768) and just fill that
portion with 0 in case it's not implemented. Note that this is just an
idea, I'm not aware of best practices in cases like this.

Adrian