netdev - Re: ethtool read EEPROM

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Message-ID: <b5dflgmqztzjmt42rw3x5ccrdth7qkc2kicr6jtofkkrmyo2cy@utly225o6zn3>
Date: Tue, 25 Mar 2025 18:03:42 +0100
From: Michal Kubecek <mkubecek@...e.cz>
To: Eliyah Havemann <eliyah@...idepacket.com>
Cc: netdev@...r.kernel.org
Subject: Re: ethtool read EEPROM

On Tue, Mar 25, 2025 at 05:16:52PM +0200, Eliyah Havemann wrote:
> Hi Michael,
> 
> You seem to be the current maintainer and top contributor to the
> ethtool project. First of all: Thank you for your contribution to OSS!
> 
> I ran into an issue with a whitebox switch with 100G and 400G QSFP
> slots, that I was hoping ethtool could solve and I want to ask you for
> assistance. It’s pretty simple: I need to read EEPROM binary data from
> these QSFP transceivers, but they are not associated with any linux
> interface. This is because vpp is controlling them directly. The
> ethtool has a function to output the EEPROM of an interface, but I
> can’t feed it the file back to it to read it. The file it outputs has
> the exact same format of the file the whitebox switch provides. I
> created a small python script to read the file and it gives reasonable
> output, but I don’t have a way to test this against a big collection
> of SFPs and I know that this work was already done in ethtool.
> 
> My questions:
> 1. Do you know of a tool that can read these files that ethtool
> outputs? Maybe it exists, and I just didn’t find it…
> 2. If not, can you provide some guidance on how to add the
> functionality to ethtool to read EEPROMs directly?

If I understand you correctly, your problem is that ethtool can
interpret the content of the module EEPROM but cannot read it for
a module in a smart switch.

In general, devlink should be the tool designed to handle smart switches
and similar devices and their components. I'm not aware if it can also
interpret the module EEPROM content like ethtool does but it's the tool
you should definitely take a look at.

Implementing a feature that would allow to use the ethtool code for
interpreting the module EEPROM content also on a dump read from a file
is something that would probably make sense whether you can use devlink
for your purpose. I'll check what would be the most appropriate way to
do that.

Michal