linux-kernel - Re: [PATCH] net: phy: microchip_t1: LAN887X: Fix device init issues.

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Message-ID: <0737ef75-b9ac-4979-8040-a3f1a83e974e@lunn.ch>
Date: Fri, 26 Sep 2025 23:46:48 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Josef Raschen <josef@...chen.org>
Cc: Arun Ramadoss <arun.ramadoss@...rochip.com>,
	UNGLinuxDriver@...rochip.com,
	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>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: phy: microchip_t1: LAN887X: Fix device init issues.

On Fri, Sep 26, 2025 at 11:24:56PM +0200, Josef Raschen wrote:
> Hello Andrew,
> 
> Thanks for your feedback.
> 
> On 9/26/25 00:00, Andrew Lunn wrote:
> > On Thu, Sep 25, 2025 at 10:52:22PM +0200, Josef Raschen wrote:
> > > Currently, for a LAN8870 phy, before link up, a call to ethtool to set
> > > master-slave fails with 'operation not supported'. Reason: speed, duplex
> > > and master/slave are not properly initialized.
> > > 
> > > This change sets proper initial states for speed and duplex and publishes
> > > master-slave states. A default link up for speed 1000, full duplex and
> > > slave mode then works without having to call ethtool.
> > 
> > Hi Josef
> > 
> > What you are missing from the commit message is an explanation why the
> > LAN8870 is special, it needs to do something no other PHY does. Is
> > there something broken with this PHY? Some register not following
> > 802.3?
> > 
> >      Andrew
> > 
> > ---
> > pw-bot: cr
> > 
> 
> Special about the LAN8870 might be that it is a dual speed T1 phy.
> As most other T1 pyhs have only one possible configuration the unknown
> speed configuration was not a problem so far. But here, when
> calling link up without manually setting the speed before, it seems to
> pick speed 100 in phy_sanitize_settings(). I assume that this is not the
> desired behavior?

What speeds does the PHY say it supports?

phy_sanitize_settings() should pick the highest speed the PHY supports
as the default. So if it is picking 100, it suggests the PHY is not
reporting it supports 1000? Or phy_sanitize_settings() is broken for
1000Base-T1? Please try understand why it is picking 100.

> The second problem is that ethtool initially does not allow to set
> master-slave at all. You first have to call ethtool without the
> master-slave argument, then again with it. This is fixed by reading
> the master slave configuration from the device which seems to be missing
> in the .config_init and .config_aneg functions. I took this solution from
> net/phy/dp83tg720.c.

How does this work with a regular T4 or T2 PHY? Ideally, A T1 should
be no different. And ideally, we want a solution for all T1 PHYs,
assuming it is not something which is special for this PHY.

	Andrew