On Wed, Aug 20, 2025 at 02:11:57PM +0200, Andrew Lunn wrote:

quoted

quoted

The doc in patch 1 says :

  > + * Link-wide mode:
  > + *  - Some PHYs only expose a link-wide aggregate MSE, or cannot map their
  > + *    measurement to a specific channel/pair (e.g. 100BASE-TX when MDI/MDI-X
  > + *    resolution is unknown). In that case, callers must use the LINK selector.

The way I understand that is that PHYs will report either channel-specific values or
link-wide values. Is that correct or are both valid ? In BaseT1 this is the same thing,
but maybe for consistency, we should report either channel values or link-wide values ?

for 100Base-T1 the LINK and channel-A selectors are effectively the
same, since the PHY only has a single channel. In this case both are
valid, and the driver will return the same answer for either request.

I decided to expose both for consistency:
- on one side, the driver already reports pair_A information for the
  cable test, so it makes sense to allow channel-A here as well;
- on the other side, if a caller such as a generic link-status/health
  request asks for LINK, we can also provide that without special
  casing.

So the driver just answers what it can. For this PHY, LINK and
channel-A map to the same hardware register, and all other selectors
return -EOPNOTSUPP.

The document you referenced explicitly says it is for 100BASE-T1.  Are
there other Open Alliance documents which extend the concept to -T2
and -T4 links? Do you have access to -T2 or -T4 PHYs which implement
the concept for multiple pairs?

So far I know, following T2/T4 PHYs support MSE:
LAN8830, KSZ9131, LAN8831, LAN8840, LAN8841
DP83826*, DP83640, DP83867*, DP83869HM

I have access at least to LAN8841.

I think it is good you are thinking about the API, how it could work
with -T2 and -T4, but do we need this complexity now?

Hm.. I just fear to make same mistake as I did with SQI. So, I analyzed
as many datasheets as possible.

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