linux-kernel - Re: [PATCH] net: marvell: mvpp2: phylink requires the link interrupt

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Message-ID: <20191214071907.GA2925@1wt.eu>
Date:   Sat, 14 Dec 2019 08:19:07 +0100
From:   Willy Tarreau <w@....eu>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Russell King <rmk+kernel@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Antoine Tenart <antoine.tenart@...tlin.com>,
        Andrew Lunn <andrew@...n.ch>,
        Thomas Bogendoerfer <tbogendoerfer@...e.de>,
        maxime.chevallier@...tlin.com, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] net: marvell: mvpp2: phylink requires the link interrupt

On Fri, Dec 13, 2019 at 04:34:03PM -0800, Jakub Kicinski wrote:
> On Tue, 10 Dec 2019 22:33:05 +0000, Russell King wrote:
> > phylink requires the MAC to report when its link status changes when
> > operating in inband modes.  Failure to report link status changes
> > means that phylink has no idea when the link events happen, which
> > results in either the network interface's carrier remaining up or
> > remaining permanently down.
> > 
> > For example, with a fiber module, if the interface is brought up and
> > link is initially established, taking the link down at the far end
> > will cut the optical power.  The SFP module's LOS asserts, we
> > deactivate the link, and the network interface reports no carrier.
> > 
> > When the far end is brought back up, the SFP module's LOS deasserts,
> > but the MAC may be slower to establish link.  If this happens (which
> > in my tests is a certainty) then phylink never hears that the MAC
> > has established link with the far end, and the network interface is
> > stuck reporting no carrier.  This means the interface is
> > non-functional.
> > 
> > Avoiding the link interrupt when we have phylink is basically not
> > an option, so remove the !port->phylink from the test.
> > 
> > Tested-by: Sven Auhagen <sven.auhagen@...eatech.de>
> > Tested-by: Antoine Tenart <antoine.tenart@...tlin.com>
> > Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>
> 
> Fixes: 4bb043262878 ("net: mvpp2: phylink support") ?
> 
> Seems like you maybe didn't want this backported to stable hence 
> no fixes tag?
> 
> Please advise :)

Speaking for myself, I'd very much like to get it into stable in order
to avoid having to keep this local patch on top of latest stable!

Willy