Re: Ethtool is missing C2C link modes

[Eric Joyner <eric.joyner@amd.com>]

On 7/10/2026 2:45 PM, D H, Siddaraju wrote:
> Hello Linux Ethernet team, Maxime, Andrew & Michal,
> 
> The IEEE AUI chip-to-chip (C2C) is the accepted standard for connecting
> chips that handle subfunctions within the OSI physical layer. Just to
> pick, the C2C is widely used when connecting Ethernet SoCs with retimers
> and PCS SerDes terminated external-phys to offload PHY sublayer functions.
> 
> With the existing ethtool link modes, we were not able to fit these C2C
> interfaces on any others (we fitted **SGMII interfaces to baseT link modes)
> and we see this as a gap. If you acknowledge this, we plan to send an
> RFC patch to define below listed C2C link modes to ethtool.
> 
> 	10G_SFI_C2C		SFF-8418
> 	25G_AUI_C2C		IEEE 802.3 Annex 109A
> 	CAUI4 C2C		IEEE 802.3 Annex 83D
> 	LAUI2-C2C		IEEE 802.3 Annex 135B
> 	50GAUI-1 C2C		IEEE 802.3 Annex 135F
> 	200GAUI-4 C2C		IEEE 802.3 Annex 120D
> 	100GAUI-1 C2C		IEEE 802.3ck Annex 120F
> 	200GAUI-2 C2C		IEEE 802.3ck Clause 162
> 	400GAUI-4 C2C		IEEE 802.3ck Clause 163
> 
> - Thank you,
> Siddaraju D H
> 

I'll piggyback on this thread because I have a related question about missing
ethtool link modes: what about entries for various Active Cable types? e.g. AOC,
ACC, and AEC for the appropriate speeds.

I see some drivers (like i40e and ice) detect these and map them to SR or DA/CR
types, but I don't see them do it in a consistent pattern, either. I couldn't
find anything that suggested a precedent on how to handle these.

- Eric