On Wed, Aug 27, 2025 at 10:13:59AM +0100, Russell King (Oracle) wrote:

On Wed, Aug 27, 2025 at 11:03:42AM +0200, Alexander Wilhelm wrote:

quoted

I asked the hardware engineer again. The point is that the MAC does not set
SGMII for 100M. It still uses 2500base-x but with 10x paket repetition.

No one uses symbol repetition when in 2500base-x mode. Nothing supports
it. Every device datasheet I've read states clearly that symbol
repetition is unsupported when operating at 2.5Gbps.

Also think about what this means. If the link is operating at 2.5Gbps
with a 10x symbol repetition, that means the link would be passing
250Mbps. That's not compatible with _anything_.

FWIW, claim 5 of this active Cisco patent suggests dividing frames into
2 segments, replicating symbols from the first segment twice and symbols
from the second segment three times.
https://patents.google.com/patent/US7356047B1/en

I'm completely unaware of any implementations of this either, though.

To remain on topic, I don't see how the hardware engineer's claim can be
true. The PCS symbol replication is done through the IF_MODE_SPEED
field, which lynx_pcs_link_up_2500basex() sets to SGMII_SPEED_2500 (same
as SGMII_SPEED_1000, i.e. no replication). You can confirm that the
IF_MODE register has the expected value by putting a print.