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

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Message-ID: <YXqq19HxleZd6V9W@shredder>
Date:   Thu, 28 Oct 2021 16:51:19 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     sundeep subbaraya <sundeep.lkml@...il.com>
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>
Subject: Re: [EXT] Re: [net-next PATCH 1/2] octeontx2-pf: Add devlink param
 to init and de-init serdes

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.

> 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".