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

[Andrew Lunn <andrew@lunn.ch>]

> 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