linux-kernel - Re: [PATCH net-next v2] net: dsa: microchip: Add SGMII port support to KSZ9477 switch

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Message-ID: <91b52099-20de-4b6e-8b05-661e598a3ef3@lunn.ch>
Date: Fri, 17 Jan 2025 14:36:13 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Tristram.Ha@...rochip.com
Cc: maxime.chevallier@...tlin.com, olteanv@...il.com,
	Woojung.Huh@...rochip.com, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, UNGLinuxDriver@...rochip.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2] net: dsa: microchip: Add SGMII port support
 to KSZ9477 switch

> The KSZ9477 SGMII module does use DesignWare IP, but its implementation
> is probably too old as some registers do not match.

Is there a revision value somewhere in the registers? Maybe the lower
nibble of ID registers 2 and 3?

> When using XPCS
> driver link detection works but the SGMII port does not pass traffic for
> some SFPs.  It is probably doable to update the XPCS driver to work in
> KSZ9477, but there is no way to submit that patch as that may affect
> other hardware implementation.

We have PHY drivers which change their behaviour based on the
revision. So it is possible. And XPCS is used quite a bit, so i don't
think it will be an issue finding somebody to do some regression
testing.

Using a PCS driver is the correct way to go here. So either you need
to copy/paste/edit the XPCS driver to create a version specific for
you hardware, or you need to extend the XPCS driver so it supports
your hardware.

	Andrew