netdev - Re: [PATCH net-next] net: sfp: cope with SFPs that set both LOS normal and LOS inverted

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Message-ID: <20210111161904.49049d9b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 11 Jan 2021 16:19:04 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Andrew Lunn <andrew@...n.ch>,
        Russell King <rmk+kernel@...linux.org.uk>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] net: sfp: cope with SFPs that set both LOS
 normal and LOS inverted

On Sun, 10 Jan 2021 17:48:15 +0100 Andrew Lunn wrote:
> On Sun, Jan 10, 2021 at 10:58:32AM +0000, Russell King wrote:
> > The SFP MSA defines two option bits in byte 65 to indicate how the
> > Rx_LOS signal on SFP pin 8 behaves:
> > 
> > bit 2 - Loss of Signal implemented, signal inverted from standard
> >         definition in SFP MSA (often called "Signal Detect").
> > bit 1 - Loss of Signal implemented, signal as defined in SFP MSA
> >         (often called "Rx_LOS").
> > 
> > Clearly, setting both bits results in a meaningless situation: it would
> > mean that LOS is implemented in both the normal sense (1 = signal loss)
> > and inverted sense (0 = signal loss).
> > 
> > Unfortunately, there are modules out there which set both bits, which
> > will be initially interpret as "inverted" sense, and then, if the LOS
> > signal changes state, we will toggle between LINK_UP and WAIT_LOS
> > states.
> > 
> > Change our LOS handling to give well defined behaviour: only interpret
> > these bits as meaningful if exactly one is set, otherwise treat it as
> > if LOS is not implemented.
> > 
> > Signed-off-by: Russell King <rmk+kernel@...linux.org.uk>  
> 
> Reviewed-by: Andrew Lunn <andrew@...n.ch>

Applied, thanks!