RE: Ethtool is missing C2C link modes

Thank you Andrew, David for bringing up all your questions.
We feel we are trending towards Maxime's intermediate link & reporting
changes but for completeness, we will start answering the open questions,
so you guys can also come up to speed and help make better design choices.

The typical AUI-C2C looks like this
RS <-MII-> PCS - PMA <-AUI-C2C-> PMA ... PMA <-AUI-C2C-> PMA - PMD <-MDI->

Andrew: Is C2C that different to CR, KR, DR?
Siddaraju: Chip-to-Chip(C2C) is simplified version of the complex KR.
	IEEE defined C2C to connect chips that cannot do KR/CR/.., especially
	the complex ANLT state-machine to negotiate, adjust equalizers, etc.

Andrew: Why break the pattern? NNbaseXY vs NN-AUI-C2C
Siddaraju: baseR is an end-to-end physical layer type that clearly defines
	the	interface & components stating from MAC RS(Reconciliation Sublayer)
	till the PMD + MDI signallings. AUI is an intermediate electrical interface
	layer(simplified KR) that connects 2 PMAs (PMA <=== AUI ===> PMA).
	AUI is a split function design approach where subfunction implementation
	from multiple vendors come together to exploit their domain expertise
	to produce a best Ethernet interconnect.

Andrew: Lane numbering at the end-to-end and other patterns..
Siddaraju: The names were just a clean copy-paste from IEEE specs Andrew.
	That was to give a clear pointings to specs and avoid confusions with
	rename/rewordings. Yes, will follow the conventions for the ethtool
	patch sets.

Andrew: I _think_ ethtool reports the media, not some intermediary format.
	Is ETHTOOL_LINK_MODE_25000baseC2C_Full_BIT actually needed? 
Siddaraju: We are here to find out that Andrew :).
	If we are following the strict convention that ethtool link modes
	report & represents the end-to-end flow "ONLY", then yes, AUI doesn't
	fit there. We are exploring phy_interface_t for intermediate interfaces
	and we hope we don't hit any roadblocks. Let's see.

David: fixed, *** more of a DT parameter than an ethtool one.
Siddaraju: I don't think so David, AUI-C2C is not a fixed/one-time config.
	All the HW offload chips that we came across so far and connects over
	AUI are multi-speed capable and depending on the MDI line rate,
	the AUI also needs reconfig/runtime	update to match the speed.
	Say if the SFP is 25G, AUI needs to be set to 25G-AUI-C2C and
	if SFP is 50G, we need 50G-AUI1-C2C.

David: Remember the history......
Siddaraju: Thank you David for highlighting this. We are in alignment with
	you and we are following a strict process to review and gain as much as
	history and conventions especially when dealing with Ethernet. We are
	reaching to multiple folks internally and Vijay Srinivasan(also CC'ed)
	is one such key contributors for us.
	From SW point of view, we are reaching to our internal Linux mailing
	threads and finally coming here for final guidance.
	
Eric: what about AOC, ACC, AEC, etc..?
Siddaraju: that's next for us Eric. We will definitely keep this in mind
	especially while modelling these offloaders.

Maxime: there's ongoing work[1] to *support nics with multiple connectors..
Siddaraju: Thanks Maksim. We are exploring and evaluating this. Meanwhile, 
	hope the above C2C related details helps you make more finer
	recommendation and we hope to hear more.

- Thank you,
Siddaraju D H