Re: [PATCH net-next v5 07/13] net: ethtool: Introduce a command to list PHYs on an interface

From: Maxime Chevallier <maxime.chevallier@bootlin.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: "Jakub Kicinski" <kuba@kernel.org>,
	davem@davemloft.net, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, thomas.petazzoni@bootlin.com,
	"Eric Dumazet" <edumazet@google.com>,
	"Paolo Abeni" <pabeni@redhat.com>,
	"Russell King" <linux@armlinux.org.uk>,
	linux-arm-kernel@lists.infradead.org,
	"Christophe Leroy" <christophe.leroy@csgroup.eu>,
	"Herve Codina" <herve.codina@bootlin.com>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	"Heiner Kallweit" <hkallweit1@gmail.com>,
	"Vladimir Oltean" <vladimir.oltean@nxp.com>,
	"Köry Maincent" <kory.maincent@bootlin.com>,
	"Jesse Brandeburg" <jesse.brandeburg@intel.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Marek Behún" <kabel@kernel.org>,
	"Piergiorgio Beruto" <piergiorgio.beruto@gmail.com>,
	"Oleksij Rempel" <o.rempel@pengutronix.de>,
	"Nicolò Veronese" <nicveronese@gmail.com>,
	"Simon Horman" <horms@kernel.org>
Subject: Re: [PATCH net-next v5 07/13] net: ethtool: Introduce a command to list PHYs on an interface
Date: Thu, 25 Jan 2024 09:22:25 +0100	[thread overview]
Message-ID: <20240125092225.45cdaa09@device-28.home> (raw)
In-Reply-To: <1092441f-c347-4f61-8405-7cc8a07d5850@lunn.ch>

On Wed, 24 Jan 2024 17:54:53 +0100
Andrew Lunn <andrew@lunn.ch> wrote:

> > > Another option might be to add PHY support to netdevsim. Add a debugfs
> > > interface to allow you to create arbitrary PHY topologies? You can
> > > then even add a test script.  
> > 
> > Sorry for the delayed answer, I just took a few hours to give it a try,
> > and I was able to spin some very basic PHY support for the netdevsim,
> > allowing to attach arbitrary instances of fixed_phy devices. I can
> > therefore use that as a mean of testing the dump operation, I'll try to
> > include that in the next iteration, that should pave the way for some
> > testability of more PHY stuff hopefully.  
> 
> Great that you looked at this.
> 
> FYI: Jakub would like to see changes to netdevsim accompanied with
> self tests making you of the features you add. There is also now a
> build bot running the self tests against net-next, so these tests
> should get run quite frequently.

No problem, I'll include these as well.

I do face a problem with fixed_phy though now that I've played around
with it. As fixed_phys share the same global MDIO bus, what can happen
is that netdevsim-registered PHYs can starve the dummy MDIO bus by
exhausting all 32 mdio addresses, preventing real interfaces from
getting their own fixed-phy instance.

I'll probably register a dedicated mdio bus per netdevsim (or even
per-phy, so that we can imagine controling the returned register
values), let's see how it goes.

Thanks,

Maxime

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