linux-kernel - Re: [PATCH net-next 2/2] net: phy: aquantia: allow forcing order of MDI pairs

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Message-ID: <ZsYTZK4Ku2LoZ4SA@makrotopia.org>
Date: Wed, 21 Aug 2024 17:18:44 +0100
From: Daniel Golle <daniel@...rotopia.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: "David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	Christian Marangi <ansuelsmth@...il.com>,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
	Robert Marko <robimarko@...il.com>,
	Russell King <rmk+kernel@...linux.org.uk>,
	Chad Monroe <chad.monroe@...ran.com>,
	John Crispin <john@...ozen.org>, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/2] net: phy: aquantia: allow forcing order of
 MDI pairs

On Wed, Aug 21, 2024 at 06:07:06PM +0200, Andrew Lunn wrote:
> On Wed, Aug 21, 2024 at 01:46:50PM +0100, Daniel Golle wrote:
> > Normally, the MDI reversal configuration is taken from the MDI_CFG pin.
> > However, some hardware designs require overriding the value configured
> > by that bootstrap pin. The PHY allows doing that by setting a bit which
> > allows ignoring the state of the MDI_CFG pin and configuring whether
> > the order of MDI pairs should be normal (ABCD) or reverse (DCBA).
> > 
> > Introduce two boolean properties which allow forcing either normal or
> > reverse order of the MDI pairs from DT.
> 
> How does this interact with ethtool -s eth42 [mdix auto|on|off]
> 
> In general, you want mdix auto, so the two ends figure out how the
> cable is wired and so it just works.

It looks like Aquantia only supports swapping pair (1,2) with pair (3,6)
like it used to be for MDI-X on 100MBit/s networks.

When all 4 pairs are in use (for 1000MBit/s or faster) the link does not
come up with pair order is not configured correctly, either using MDI_CFG
pin or using the "PMA Receive Reserved Vendor Provisioning 1" register.

And yes, I did verify that Auto MDI-X is enabled in the
"Autonegotiation Reserved Vendor Provisioning 1" register.