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

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Date: Wed, 15 May 2024 17:10:51 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Thomas Geßler <gessler_t@...eckmann-gmbh.de>
Cc: Thomas Gessler <thomas.gessler@...eckmann-gmbh.de>,
	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 Wed, May 15, 2024 at 10:15:33AM +0200, Thomas Geßler wrote:
> On Tue, 14 May 2024, Andrew Lunn wrote:
> > On Tue, May 14, 2024 at 02:27:28PM +0200, Thomas Gessler wrote:
> > > 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?
> 
> Basically. I would call this an RGMII-SGMII bridge. A "media converter" I
> would call a device that changes the physical medium, like 1000BASE-T
> copper/RJ45 to 1000BASE-X fiber/SFP.
> 
> We have this chip on a daughter card with exposed SGMII lines that can be
> plugged into customer-specific motherboards. The motherboard will have
> either an SGMII-copper PHY (this can also be a DP83869) with 10/100/1000
> auto-neg enabled but without MDIO exposed to the CPU on the daughter card;
> or an SFP cage. The SFP module, in turn, can be for 1000BASE-X fiber,
> 1000BASE-X-to-1000-BASE-T copper, or SGMII copper supporting 10/100/1000
> auto-neg.

The SFP use case is probably not too hard to support. There are PHYs
drivers today which have the needed plumbing for this. Look at the
marvell10g driver, its mv3310_sfp_ops. qcom/qca807x.c: qca807x_sfp_ops
etc.

	Andrew