Re: Unsupported phy-connection-type sgmii-2500 in arch/powerpc/boot/dts/fsl/t1023rdb.dts

On Friday 04 June 2021 20:27:33 Russell King (Oracle) wrote:

802.3 defined 1000base-X which is a fixed 1G speed interface using a
16-bit control word. Implementations of this exist where the control
word can be disabled.

Cisco came along, took 1000base-X and augmented it to allow speeds of
10M and 100M by symbol repetition, and changing the format of the
16-bit control word. Otherwise, it is functionally compatible - indeed
SGMII with the control word disabled will connect with 1000base-X with
the control word disabled. I've done it several times.

There exists 2500base-X, which is 1000base-X clocked faster, and it
seems the concensus is that it has the AN disabled - in other words,
no control word.

Thank you for a nice explanation! I think that this information should
be part of documentation as it could help also other people to
understand differences between these modes.