Re: [PATCH 1/8] net: phy: realtek: rtl8221: allow to configure SERDES mode

[Daniel Golle]

On Thu, May 11, 2023 at 02:38:19AM +0200, Andrew Lunn wrote:
> > +#define RTL8221B_SERDES_OPTION_MODE_2500BASEX_SGMII	0
> > +#define RTL8221B_SERDES_OPTION_MODE_HISGMII_SGMII	1
> > +#define RTL8221B_SERDES_OPTION_MODE_2500BASEX		2
> 
> So what is 2500BASEX_SGMII? You cannot run SGMII at 2.5G, because
> there is no way to repeat a symbol 2.5 times so that a 1G stream takes
> up 2.5G bandwidth. The SGMII signalling also does not work at 2.5G.

*_MODE_2500BASEX_SGMII means that the PHY will dynamically switch
interface mode between 2500Base-X for 2500M links and SGMII for
everything else.

Setting  *_MODE_2500BASEX in contrast to that enabled rate-adapter mode
and always uses 2500Base-X no matter what the speed of the link on the
TP interface is.

I will add a comment explaining that.