netdev - Re: [RFC PATCH net-next 0/4] ethtool: Add ability to flash and query transceiver modules' firmware

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Date:   Mon, 29 Nov 2021 19:05:21 +0100
From:   Michal Kubecek <mkubecek@...e.cz>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Ido Schimmel <idosch@...sch.org>, netdev@...r.kernel.org,
        davem@...emloft.net, andrew@...n.ch, pali@...nel.org,
        jacob.e.keller@...el.com, vadimp@...dia.com, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [RFC PATCH net-next 0/4] ethtool: Add ability to flash and query
 transceiver modules' firmware

On Mon, Nov 29, 2021 at 09:37:24AM -0800, Jakub Kicinski wrote:
> On Sat, 27 Nov 2021 19:45:26 +0200 Ido Schimmel wrote:
> > This patchset extends the ethtool netlink API to allow user space to
> > both flash transceiver modules' firmware and query the firmware
> > information (e.g., version, state).
> > 
> > The main use case is CMIS compliant modules such as QSFP-DD. The CMIS
> > standard specifies the interfaces used for both operations. See section
> > 7.3.1 in revision 5.0 of the standard [1].
> > 
> > Despite the immediate use case being CMIS compliant modules, the user
> > interface is kept generic enough to accommodate future use cases, if
> > these arise.
> > 
> > The purpose of this RFC is to solicit feedback on both the proposed user
> > interface and the device driver API which are described in detail in
> > patches #1 and #3. The netdevsim patches are for RFC purposes only. The
> > plan is to implement the CMIS functionality in common code (under lib/)
> > so that it can be shared by MAC drivers that will pass function pointers
> > to it in order to read and write from their modules EEPROM.
> > 
> > ethtool(8) patches can be found here [2].
> 
> Immediate question I have is why not devlink. We purposefully moved 
> FW flashing to devlink because I may take long, so doing it under
> rtnl_lock is really bad. Other advantages exist (like flashing
> non-Ethernet ports). Ethtool netlink already existed at the time.

Note that ethtool (as userspace utility) can still provide the
functionality even if it's implemented in devlink API; this is likely
going to be the case for device EEPROM flash (ethtool -f). At the
moment, there is a problem that not nearly every device capable of
flashing implements devlink but that could be addressed by the "generic
devlink" idea (a wrapper implementing selected parts of devlink API for
devices without an actual devlink implementation).

Michal