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

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Message-ID: <a30d00cd-9148-423b-a3e5-b11d6c5c270b@bootlin.com>
Date: Fri, 22 Aug 2025 12:09:22 +0200
From: Maxime Chevallier <maxime.chevallier@...tlin.com>
To: "Russell King (Oracle)" <linux@...linux.org.uk>
Cc: davem@...emloft.net, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 thomas.petazzoni@...tlin.com, Andrew Lunn <andrew@...n.ch>,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, 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>,
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 Marek Behún <kabel@...nel.org>,
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 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

Hello Russell,

I'm re-replying here even though a more recent version was sent, as I 
realise I forgot to fully address that.

On 27/07/2025 11:56, Russell King (Oracle) wrote:
> On Tue, Jul 22, 2025 at 02:16:12PM +0200, Maxime Chevallier wrote:
>> +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);
>> +
>> +	__ETHTOOL_DECLARE_LINK_MODE_MASK(sfp_support);
>> +	DECLARE_PHY_INTERFACE_MASK(interfaces);
>> +	phy_interface_t iface;
>> +
>> +	linkmode_zero(sfp_support);
>> +
>> +	if (!port)
>> +		return -EINVAL;
>> +
>> +	sfp_parse_support(phydev->sfp_bus, id, sfp_support, interfaces);
>> +
>> +	if (phydev->n_ports == 1)
>> +		phydev->port = sfp_parse_port(phydev->sfp_bus, id, sfp_support);
>> +
>> +	linkmode_and(sfp_support, port->supported, sfp_support);
>> +
>> +	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);
> 
> I've been moving phylink away from using sfp_select_interface() because
> it requires two stages of translation - one from the module capabilties
> to linkmodes, and then linkmodes to interfaces.
> 
> sfp_parse_support() now provides the interfaces that the optical module
> supports, and the possible interfaces that a copper module _might_
> support (but we don't know for certain about that until we discover a
> PHY.)
> 
> The only place in phylink where this function continues to be used is
> when there's an optical module which supports multiple different
> speeds, and we need to select it based on the advertising mask provided
> by userspace. Everywhere else shouldn't use this function, but should
> instead use the interfaces returned from sfp_parse_support().
> 

In any case, we'll eventually have to select one of the interfaces if 
there are multiple matches from the sfp_parse_support. phylink maintains 
a sorted list of interfaces used as a preference, I think we should use 
the same list for phy-driver SFP. I'm thinking about moving 
phylink_choose_sfp_interface() in the sfp code, would you be OK with that ?

Maxime