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:   Wed, 27 Oct 2021 21:11:59 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     sundeep subbaraya <sundeep.lkml@...il.com>,
        David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
        hariprasad <hkelam@...vell.com>,
        Geetha sowjanya <gakula@...vell.com>,
        Sunil Kovvuri Goutham <sgoutham@...vell.com>,
        Subbaraya Sundeep <sbhatta@...vell.com>,
        Rakesh Babu <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 Wed, Oct 27, 2021 at 10:08:57AM -0700, Jakub Kicinski wrote:
> On Wed, 27 Oct 2021 22:13:32 +0530 sundeep subbaraya wrote:
> > > On Wed, 27 Oct 2021 16:01:14 +0530 Subbaraya Sundeep wrote:  
> > > > From: Rakesh Babu <rsaladi2@...vell.com>
> > > >
> > > > The physical/SerDes link of an netdev interface is not
> > > > toggled on interface bring up and bring down. This is
> > > > because the same link is shared between PFs and its VFs.
> > > > This patch adds devlink param to toggle physical link so
> > > > that it is useful in cases where a physical link needs to
> > > > be re-initialized.  
> > >
> > > So it's a reset? Or are there cases where user wants the link
> > > to stay down?  
> > 
> > There are cases where the user wants the link to stay down and debug.
> > We are adding this to help customers to debug issues wrt physical links.
> 
> Intel has a similar thing, they keep adding a ethtool priv flag called 
> "link-down-on-close" to all their drivers.

This is the list I compiled the previous time we discussed it:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c3880bd159d431d06b687b0b5ab22e24e6ef0070
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d5ec9e2ce41ac198de2ee18e0e529b7ebbc67408
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ab4ab73fc1ec6dec548fa36c5e383ef5faa7b4c1

It seems that various drivers default to not shutting down the link upon
ndo_stop(), but some users want to override it. I hit that too as it
breaks ECMP (switch thinks the link is up).

> Maybe others do this, too.  It's time we added a standard API for
> this.

The new parameter sounds like a reset, but it can also be achieved by:

# ethtool --set-priv-flags eth0 link-down-on-close on
# ip link set dev eth0 down
# ip link set dev eth0 up

Where the first command is replaced by a more standard ethtool API.