Re: [PATCH net-next 4/4] net: dsa: microchip: add SGMII port support to KSZ9477 switch

[Andrew Lunn]

On Fri, Aug 09, 2024 at 04:38:40PM -0700, Tristram.Ha@xxxxxxxxxxxxx wrote:
> From: Tristram Ha <tristram.ha@xxxxxxxxxxxxx>
> 
> The SGMII module of KSZ9477 switch can be setup in 3 ways: 0 for direct
> connect, 1 for 1000BaseT SFP, and 2 for 10/100/1000 SFP.
> 
> SFP is typically used so the default is 1.  The driver can detect
> 10/100/1000 SFP and change the mode to 2.  For direct connect this mode
> has to be explicitly set to 0 as driver cannot detect that
> configuration.

Is 1 actually 1000BaseX? An SFP module using fibre would typically
want 1000BaseX, and only support one speed. An SFP module using copper
typically has a PHY in it, it performs auto-neg on the media side, and
then uses SGMII inband signalling to tell the MAC what data rate,
symbol duplication to do. And maybe mode 0 has in-band signalling
turned off, in which case 1000BaseX and SGMII become identical,
because it is the signalling which is different.

	Andrew