netdev - Re: [EXT] Re: [net-next PATCH 1/2] octeontx2-pf: Add devlink param to init and de-init serdes

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Date:   Sat, 30 Oct 2021 12:55:47 +0530
From:   sundeep subbaraya <sundeep.lkml@...il.com>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Sunil Kovvuri Goutham <sgoutham@...vell.com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Hariprasad Kelam <hkelam@...vell.com>,
        Geethasowjanya Akula <gakula@...vell.com>,
        Subbaraya Sundeep Bhatta <sbhatta@...vell.com>,
        Rakesh Babu Saladi <rsaladi2@...vell.com>,
        Saeed Mahameed <saeed@...nel.org>,
        "anthony.l.nguyen@...el.com" <anthony.l.nguyen@...el.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Andrew Lunn <andrew@...n.ch>, argeorge@...co.com
Subject: Re: [EXT] Re: [net-next PATCH 1/2] octeontx2-pf: Add devlink param to
 init and de-init serdes

Hi Ido,

On Thu, Oct 28, 2021 at 7:21 PM Ido Schimmel <idosch@...sch.org> wrote:
>
> On Thu, Oct 28, 2021 at 05:48:02PM +0530, sundeep subbaraya wrote:
> > Actually we also need a case where debugging is required when the
> > logical link is
> > up (so that packets flow from kernel to SerDes continuously) but the
> > physical link
> > is down.
>
> Can you explain the motivation for that? In the past we discussed use
> cases for forcing the operational state to down while the administrative
> state is up and couldn't find any.
>
To be honest we got this request from a customer to provide a command to modify
physical link without tying it to a logical link. I have asked for
more details on how
they use it.

> > We will change the commit description since it is giving the
> > wrong impression.
> > A command to change physical link up/down with no relation to ifconfig
> > is needed.
>
> So it is obvious that some drivers default to not shutting down the
> physical link upon admin down, but that some users want to change that.
> In addition, we have your use case to control the physical link without
> relation to the logical link. I wonder if it can all be solved with a
> new ethtool attribute (part of LINKINFO_{SET,GET} ?) that describes the
> physical link policy and has the following values:
>
> * auto: Physical link state is derived from logical link state
> * up: Physical link state is always up
> * down: Physical link state is always down
>
> IIUC, it should solve your problem and that of the "link-down-on-close"
> private flag. It also has the added benefit of allowing user space to
> query the default policy. The expectation is that it would be "auto",
> but in some scenarios it is "up".

This looks good. Please note that we need the behavior such that after changing
the flag a subsequent ifconfig command is not needed by the user.

auto : in ndo_open, ndo_close check the physical link flag is auto and
send command
          to firmware for bringing physical link up/down.
up: send command to firmware instantaneously for physical link UP
down: send command to firmware instantaneously for physical link DOWN

Thanks,
Sundeep