linux-kernel - Re: [PATCH net-next v10 07/15] net: phy: Introduce generic SFP handling for PHY drivers

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Message-ID: <20250804154949.49cbed6f@fedora.home>
Date: Mon, 4 Aug 2025 15:49:49 +0200
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 thomas.petazzoni@...tlin.com, Jakub Kicinski <kuba@...nel.org>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Russell
 King <linux@...linux.org.uk>, linux-arm-kernel@...ts.infradead.org,
 Christophe Leroy <christophe.leroy@...roup.eu>, Herve Codina
 <herve.codina@...tlin.com>, Florian Fainelli <f.fainelli@...il.com>, Heiner
 Kallweit <hkallweit1@...il.com>, Vladimir Oltean <vladimir.oltean@....com>,
 Köry Maincent <kory.maincent@...tlin.com>, Marek
 Behún <kabel@...nel.org>, Oleksij Rempel
 <o.rempel@...gutronix.de>, Nicolò Veronese
 <nicveronese@...il.com>, Simon Horman <horms@...nel.org>,
 mwojtas@...omium.org, Antoine Tenart <atenart@...nel.org>,
 devicetree@...r.kernel.org, Conor Dooley <conor+dt@...nel.org>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Rob Herring <robh@...nel.org>, Romain
 Gantois <romain.gantois@...tlin.com>, Daniel Golle <daniel@...rotopia.org>,
 Dimitri Fedrau <dimitri.fedrau@...bherr.com>
Subject: Re: [PATCH net-next v10 07/15] net: phy: Introduce generic SFP
 handling for PHY drivers

On Sat, 26 Jul 2025 23:05:33 +0200
Andrew Lunn <andrew@...n.ch> wrote:

> On Tue, Jul 22, 2025 at 02:16:12PM +0200, Maxime Chevallier wrote:
> > There are currently 4 PHY drivers that can drive downstream SFPs:
> > marvell.c, marvell10g.c, at803x.c and marvell-88x2222.c. Most of the
> > logic is boilerplate, either calling into generic phylib helpers (for
> > SFP PHY attach, bus attach, etc.) or performing the same tasks with a
> > bit of validation :
> >  - Getting the module's expected interface mode
> >  - Making sure the PHY supports it
> >  - Optionnaly perform some configuration to make sure the PHY outputs  
> 
> Too man n's.
> 
> > +static int phy_sfp_module_insert(void *upstream, const struct sfp_eeprom_id *id)
> > +{
> > +	struct phy_device *phydev = upstream;
> > +	struct phy_port *port = phy_get_sfp_port(phydev);  
> 
> Strictly speeding, this is not allowed, reverse Christmas tree...
> 
> The assignment needs to move into the body of the function.
> 
> > +	if (linkmode_empty(sfp_support)) {
> > +		dev_err(&phydev->mdio.dev, "incompatible SFP module inserted\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	iface = sfp_select_interface(phydev->sfp_bus, sfp_support);
> > +
> > +	/* Check that this interface is supported */
> > +	if (!test_bit(iface, port->interfaces)) {
> > +		dev_err(&phydev->mdio.dev, "incompatible SFP module inserted\n");  
> 
> Maybe make this string different to the previous one, so somebody
> debugging issues knows which happened?
> 
> > +/**
> > + * phy_get_sfp_port() - Returns the first valid SFP port of a PHY
> > + * @phydev: pointer to the PHY device to get the SFP port from
> > + *
> > + * Returns: The first active SFP (serdes) port of a PHY device, NULL if none
> > + * exist.
> > + */
> > +struct phy_port *phy_get_sfp_port(struct phy_device *phydev)
> > +{
> > +	struct phy_port *port;
> > +
> > +	list_for_each_entry(port, &phydev->ports, head)
> > +		if (port->active && port->is_mii)  
> 
> Naming is hard, but this actually returns the first mii port.  Is
> there a clear 1:1 mapping? I don't think i've ever seen it, but such a
> SERDES port could be connected to a Ethernet switch? And when you get
> further, add support for a MUX, could it be connected to a MUX?

Hmmm correct, that's a bit fragile. With a mux or a switch that could
be different indeed. There may even be PHYs with 2 MII interfaces one
day ?

So yes it's most of a time a 1:1 mapping but it doesn't have to, I'll
see how I can make that more reliable...

Thanks for the review,

Maxim