netdev - Re: [PATCH 2/2] net: phy: dp83869: Fix RGMII-SGMII and 1000BASE-X

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Message-ID: <38bc6947-391b-478d-ab71-6cc8d9428275@lunn.ch>
Date: Tue, 14 May 2024 14:56:16 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Thomas Gessler <thomas.gessler@...eckmann-gmbh.de>
Cc: 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,
	MD Danish Anwar <danishanwar@...com>,
	Ravi Gunasekaran <r-gunasekaran@...com>
Subject: Re: [PATCH 2/2] net: phy: dp83869: Fix RGMII-SGMII and 1000BASE-X

On Tue, May 14, 2024 at 02:27:28PM +0200, Thomas Gessler wrote:
> The PHY supports multiple modes of which not all are properly
> implemented by the driver. In the case of the RGMII-to-SGMII and
> 1000BASE-X modes, this was primarily due to the use of non-standard
> registers for auto-negotiation settings and link status. This patch adds
> device-specific get_features(), config_aneg(), aneg_done(), and
> read_status() functions for these modes. They are based on the genphy_*
> versions with the correct registers and fall back to the genphy_*
> versions for other modes.
> 
> The RGMII-to-SGMII mode is special, because the chip does not really act
> as a PHY in this mode but rather as a bridge.

It is known as a media converter. You see them used between an RGMII
port and an SFP cage. Is that your use case?

It requires a connected
> SGMII PHY and gets the negotiated speed and duplex from it through SGMII
> auto-negotiation. To use the DP83869 as a virtual PHY, we assume that
> the connected SGMII PHY supports 10/100/1000M half/full duplex and
> therefore support and always advertise those settings.

Not all copper SFP modules support auto-neg. This is all really messy
because there is no standardisation. Also 1000BaseT_Half is often not
supported.

	Andrew