linux-kernel - Re: [PATCH net-next 0/2] net: phy: sfp: Add single-byte SMBus SFP access

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Message-ID: <20250224103526.5164e637@fedora>
Date: Mon, 24 Feb 2025 10:35:26 +0100
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: Bjørn Mork <bjorn@...k.no>, Andrew Lunn <andrew@...n.ch>,
 davem@...emloft.net, Jakub Kicinski <kuba@...nel.org>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Heiner Kallweit
 <hkallweit1@...il.com>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com, Florian
 Fainelli <f.fainelli@...il.com>, Köry Maincent
 <kory.maincent@...tlin.com>, Simon Horman <horms@...nel.org>, Romain
 Gantois <romain.gantois@...tlin.com>, Antoine Tenart <atenart@...nel.org>,
 Marek Behún <kabel@...nel.org>
Subject: Re: [PATCH net-next 0/2] net: phy: sfp: Add single-byte SMBus SFP
 access

On Mon, 24 Feb 2025 08:47:18 +0000
"Russell King (Oracle)" <linux@...linux.org.uk> wrote:

> On Mon, Feb 24, 2025 at 08:13:22AM +0100, Bjørn Mork wrote:
> > Andrew Lunn <andrew@...n.ch> writes:
> >   
> > >> So, not only do I think that hwmon should be disabled if using SMBus,
> > >> but I also think that the kernel should print a warning that SMBus is
> > >> being used and therefore e.g. copper modules will be unreliable. We
> > >> don't know how the various firmwares in various microprocessors that
> > >> convert I2C to MDIO will behave when faced with SMBus transfers.  
> > >
> > > I agree, hwmon should be disabled, and that the kernel should printing
> > > a warning that the hardware is broken and that networking is not
> > > guaranteed to be reliable.  
> > 
> > What do you think will be the effect of such a warning?  Who is the
> > target audience?
> > 
> > You can obviously add it, and I don't really care.  But I believe the
> > result will be an endless stream of end users worrying about this scary
> > warning and wanting to know what they can do about it.  What will be
> > your answer?  
> 
> ... which is good, because it raises the visibility of crap hardware
> and will make people think twice about whether to purchase it, thus
> penalising (a little) the sales of badly designed hardware.

It's also going to allow users to understand a bit more why all
features aren't available. Plugging modules in a true i2c connected
cage will report all the features, while plugging on an smbus cage will
cause the use of a degraded mode. Not only for hwmon, but as Russell
specifies, I doubt all SFP PHY will behave exactly the same...

I'll respin without hwmon and with the warning then.

Maxime