netdev - Re: [PATCH net-next v2 0/3] ethtool: support for forward error correction mode setting on a link

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Date:   Fri, 28 Jul 2017 19:29:57 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Jakub Kicinski <kubakici@...pl>
Cc:     Roopa Prabhu <roopa@...ulusnetworks.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "John W. Linville" <linville@...driver.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Vidya Sagar Ravipati <vidya.chowdary@...il.com>,
        Dustin Byford <dustin@...ulusnetworks.com>,
        Dave Olson <olson@...ulusnetworks.com>,
        Casey Leedom <leedom@...lsio.com>,
        Gal Pressman <galp@...lanox.com>,
        Manoj Malviya <manojmalviya@...lsio.com>,
        Santosh Rastapur <santosh@...lsio.com>, yuval.mintz@...gic.com,
        odedw@...lanox.com, Ariel Almog <ariela@...lanox.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Subject: Re: [PATCH net-next v2 0/3] ethtool: support for forward error
 correction mode setting on a link

On Fri, Jul 28, 2017 at 09:46:20AM -0700, Jakub Kicinski wrote:
> On Fri, 28 Jul 2017 07:53:01 -0700, Roopa Prabhu wrote:
> > On Thu, Jul 27, 2017 at 7:33 PM, Jakub Kicinski <kubakici@...pl> wrote:
> > > On Thu, 27 Jul 2017 16:47:25 -0700, Roopa Prabhu wrote:  
> > >> From: Roopa Prabhu <roopa@...ulusnetworks.com>
> > >>
> > >> Forward Error Correction (FEC) modes i.e Base-R
> > >> and Reed-Solomon modes are introduced in 25G/40G/100G standards
> > >> for providing good BER at high speeds. Various networking devices
> > >> which support 25G/40G/100G provides ability to manage supported FEC
> > >> modes and the lack of FEC encoding control and reporting today is a
> > >> source for interoperability issues for many vendors.
> > >> FEC capability as well as specific FEC mode i.e. Base-R
> > >> or RS modes can be requested or advertised through bits D44:47 of base link
> > >> codeword.
> > >>
> > >> This patch set intends to provide option under ethtool to manage and
> > >> report FEC encoding settings for networking devices as per IEEE 802.3
> > >> bj, bm and by specs.
> > >>
> > >> v2 :
> > >>         - minor patch format fixes and typos pointed out by Andrew
> > >>         - there was a pending discussion on the use of 'auto' vs
> > >>           'automatic' for fec settings. I have left it as 'auto'
> > >>           because in most cases today auto is used in place of
> > >>           automatic to represent automatically generated values.
> > >>           We use it in other networking config too. I would prefer
> > >>           leaving it as auto.  
> > >
> > > On the subject of resetting the values when module is replugged I
> > > assume what was previously described remains:
> > >  - we always allow users to set the FEC regardless of the module type;
> > >  - if user set an incorrect FEC for the module type (or module gets
> > >    swapped) the link will be administratively taken down by either
> > >    the driver or FW.
> > >
> > > Is that correct?  Am I misremembering?  
> > 
> > yes, correct. And possible future sfp hotplug events can give user-space
> > more info to react to module type changes etc.
> 
> OK, if nobody else objects and we go with that - lets make sure we
> document clearly those are expected :)  My concern is that if there is
> ever 10G + RS FEC standard we don't want to end up in a situation where
> some drivers silently ignore FEC settings in 10G and other apply it.
> So let's make it clear what the intended Linux behaviour is.  It could
> be in the ethtool man page, or the kernel somewhere.

You might also find this interesting:

https://py3.patchwork.dja.id.au/patch/42846/

Most of the rest of the series has been reviewed, so i don't think it
will be too long before it is in the kernel.

	Andrew