linux-kernel - Re: [PATCH net-next v13 05/13] net: ethtool: Allow passing a phy index for some commands

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Date: Sun, 16 Jun 2024 17:21:25 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc: Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	thomas.petazzoni@...tlin.com, 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>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Marek Behún <kabel@...nel.org>,
	Piergiorgio Beruto <piergiorgio.beruto@...il.com>,
	Oleksij Rempel <o.rempel@...gutronix.de>,
	Nicolò Veronese <nicveronese@...il.com>,
	Simon Horman <horms@...nel.org>, mwojtas@...omium.org,
	Nathan Chancellor <nathan@...nel.org>,
	Antoine Tenart <atenart@...nel.org>
Subject: Re: [PATCH net-next v13 05/13] net: ethtool: Allow passing a phy
 index for some commands

On Sun, Jun 16, 2024 at 06:02:31PM +0200, Maxime Chevallier wrote:
> Hello Jakub,
> 
> On Thu, 13 Jun 2024 18:26:13 -0700
> Jakub Kicinski <kuba@...nel.org> wrote:
> 
> > On Fri,  7 Jun 2024 09:18:18 +0200 Maxime Chevallier wrote:
> > > +		if (tb[ETHTOOL_A_HEADER_PHY_INDEX]) {
> > > +			struct nlattr *phy_id;
> > > +
> > > +			phy_id = tb[ETHTOOL_A_HEADER_PHY_INDEX];
> > > +			phydev = phy_link_topo_get_phy(dev,
> > > +						       nla_get_u32(phy_id));  
> > 
> > Sorry for potentially repeating question (please put the answer in the
> > commit message) - are phys guaranteed not to disappear, even if the
> > netdev gets closed? this has no rtnl protection
> 
> I'll answer here so that people can correct me if I'm wrong, but I'll
> also add it in the commit logs as well (and possibly with some fixes
> depending on how this discussion goes)
> 
> While a PHY can be attached to/detached from a netdevice at open/close,
> the phy_device itself will keep on living, as its lifetime is tied to
> the underlying mdio_device (however phy_attach/detach take a ref on the
> phy_device, preventing it from vanishing while it's attached to a
> netdev)

It gets interesting with copper SFP. They contain a PHY, and that PHY
can physically disappear at any time. What i don't know is when the
logical representation of the PHY will disappear after the hotunplug
event.

	Andrew