netdev - Re: [PATCH net-next 1/6] net: phy: dp83869: Disable autonegotiation in RGMII/1000Base-X mode

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Date: Tue, 2 Jul 2024 10:24:18 +0100
From: "Russell King (Oracle)" <linux@...linux.org.uk>
To: Romain Gantois <romain.gantois@...tlin.com>
Cc: Andrew Lunn <andrew@...n.ch>, Heiner Kallweit <hkallweit1@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 1/6] net: phy: dp83869: Disable autonegotiation
 in RGMII/1000Base-X mode

On Tue, Jul 02, 2024 at 10:44:12AM +0200, Romain Gantois wrote:
> To be clear, "fiber mode" in the DP83869 linguo also includes
> 1000Base-X which can be used with a direct-attach copper cable. From
> what I've seen, autonegotiation is not supported in this configuration.

Why? Direct-attached cables are 1000base-CX, which is defined by 802.3.
It uses the 1000base-X PCS which is shared with 1000base-SX, 1000base-LX
etc. If one looks at 37.1.3, Relationship to architectural layering,
or 36.1.5, Inter-sublayer interfaces, one can see in that diagram that
the PCS *including* auto-negotiation is included for SX, LX *and* CX.

Moreover, 39.3 states that TP1 and TP4 will be commin in many
implementations of LX, SX and CX.

Moreover, 39.1, 1000base-CX introduction, states that it incorporates
clause 36 and clause 38. Clause 36.2.2 states that the 1000base-X PCS
incorporates clause 37 auto-negotiation.

So, I think AN is supposed to be supported on CX in the same way that
it's supported for SX and LX.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!