netdev - Re: [net-next 3/3] net: phy: marvell-88q2xxx: Enable auto negotiation for mv88q2110

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Message-ID: <CAD4aGmRrofQzh56BSJKhmQnVM6qC8yLYuBsukirttZak26vRHQ@mail.gmail.com>
Date: Tue, 10 Sep 2024 19:02:44 +0100
From: Stefan Eichenberger <eichest@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>, 
	Heiner Kallweit <hkallweit1@...il.com>, Russell King <linux@...linux.org.uk>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Dimitri Fedrau <dima.fedrau@...il.com>, 
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>, netdev@...r.kernel.org, 
	linux-renesas-soc@...r.kernel.org
Subject: Re: [net-next 3/3] net: phy: marvell-88q2xxx: Enable auto negotiation
 for mv88q2110

Hi Andrew and Niklas,

On Tue, 10 Sept 2024 at 17:32, Andrew Lunn <andrew@...n.ch> wrote:
>
> On Fri, Sep 06, 2024 at 11:39:23PM +0200, Niklas Söderlund wrote:
> > On 2024-09-06 22:36:49 +0200, Andrew Lunn wrote:
> > > On Fri, Sep 06, 2024 at 03:39:51PM +0200, Niklas Söderlund wrote:
> > > > The initial marvell-88q2xxx driver only supported the Marvell 88Q2110
> > > > PHY without auto negotiation support. The reason documented states that
> > > > the provided initialization sequence did not to work. Now a method to
> > > > enable auto negotiation have been found by comparing the initialization
> > > > of other supported devices and an out-of-tree PHY driver.
> > > >
> > > > Perform the minimal needed initialization of the PHY to get auto
> > > > negotiation working and remove the limitation that disables the auto
> > > > negotiation feature for the mv88q2110 device.
> > > >
> > > > With this change a 1000Mbps full duplex link is able to be negotiated
> > > > between two mv88q2110 and the link works perfectly. The other side also
> > > > reflects the manually configure settings of the master device.
> > > >
> > > >     # ethtool eth0
> > > >     Settings for eth0:
> > > >             Supported ports: [  ]
> > > >             Supported link modes:   100baseT1/Full
> > > >                                     1000baseT1/Full
> > > >             Supported pause frame use: Symmetric Receive-only
> > > >             Supports auto-negotiation: Yes
> > >
> > > My understanding is that most automotive applications using T1 don't
> > > actually want auto-neg, because it is slow. Given the static use case,
> > > everything can be statically configured.
> > >
> > > Is there a danger this change is going to cause regressions? There are
> > > users who are happy for it to use 100BaseT1 without negotiation, and
> > > the link partner is not offering any sort of negotiation. But with
> > > this change, autoneg is now the default, and the link fails to come
> > > up?
> >
> > I'm not sure how the generic use-case looks like. All I can say all
> > other devices supported by this driver support autoneg by default and
> > the initial commit adds some of the autoneg features but disables it
> > with a comment that they could not get it to work.
>
> I'm just worried about reports of regressions. It could be you are
> currently the only user of this driver, and you obviously don't care
> about the change in behaviour, and can change the configuration of the
> other end so that it also does autoneg.
>
> But then again, Stefan Eichenberger <eichest@...il.com> added this
> driver. Does autoneg by default, not forced, cause problems for his
> systems?

Sorry I didn't reply before, I'm currently travelling. That's also why I
couldn't test the changes yet.

For our use case the proposed change shouldn't be an issue.
We anyway need to configure the speed from userspace. So I think
the proposed change is fine from a user's perspective. It will require
user space to configure the interface correctly before it starts the
interface or it will fallback to autoneg.

Regards,
Stefan