linux-kernel - Re: [PATCH net-next v2 5/5] net: phy: dp83td510: add MSE interface support for 10BASE-T1L

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Message-ID: <aKW-3sF2g2QrKDpG@pengutronix.de>
Date: Wed, 20 Aug 2025 14:26:06 +0200
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Andrew Lunn <andrew@...n.ch>
Cc: Maxime Chevallier <maxime.chevallier@...tlin.com>,
	Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>,
	Donald Hunter <donald.hunter@...il.com>,
	Jonathan Corbet <corbet@....net>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Kory Maincent <kory.maincent@...tlin.com>,
	Nishanth Menon <nm@...com>, kernel@...gutronix.de,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	UNGLinuxDriver@...rochip.com, linux-doc@...r.kernel.org,
	Michal Kubecek <mkubecek@...e.cz>, Roan van Dijk <roan@...tonic.nl>
Subject: Re: [PATCH net-next v2 5/5] net: phy: dp83td510: add MSE interface
 support for 10BASE-T1L

On Wed, Aug 20, 2025 at 02:11:57PM +0200, Andrew Lunn wrote:
> > > The doc in patch 1 says :
> > > 
> > >   > + * Link-wide mode:
> > >   > + *  - Some PHYs only expose a link-wide aggregate MSE, or cannot map their
> > >   > + *    measurement to a specific channel/pair (e.g. 100BASE-TX when MDI/MDI-X
> > >   > + *    resolution is unknown). In that case, callers must use the LINK selector.
> > > 
> > > The way I understand that is that PHYs will report either channel-specific values or
> > > link-wide values. Is that correct or are both valid ? In BaseT1 this is the same thing,
> > > but maybe for consistency, we should report either channel values or link-wide values ?
> > 
> > for 100Base-T1 the LINK and channel-A selectors are effectively the
> > same, since the PHY only has a single channel. In this case both are
> > valid, and the driver will return the same answer for either request.
> > 
> > I decided to expose both for consistency:
> > - on one side, the driver already reports pair_A information for the
> >   cable test, so it makes sense to allow channel-A here as well;
> > - on the other side, if a caller such as a generic link-status/health
> >   request asks for LINK, we can also provide that without special
> >   casing.
> > 
> > So the driver just answers what it can. For this PHY, LINK and
> > channel-A map to the same hardware register, and all other selectors
> > return -EOPNOTSUPP.
> 
> The document you referenced explicitly says it is for 100BASE-T1.  Are
> there other Open Alliance documents which extend the concept to -T2
> and -T4 links? Do you have access to -T2 or -T4 PHYs which implement
> the concept for multiple pairs?

So far I know, following T2/T4 PHYs support MSE:
LAN8830, KSZ9131, LAN8831, LAN8840, LAN8841
DP83826*, DP83640, DP83867*, DP83869HM

I have access at least to LAN8841.

> I think it is good you are thinking about the API, how it could work
> with -T2 and -T4, but do we need this complexity now?

Hm.. I just fear to make same mistake as I did with SQI. So, I analyzed
as many datasheets as possible.

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