[PATCH RFC net-next 0/9] net: introduce Qualcomm XPCS support and add Nord Ethernet plumbing

[Coia Prant]

Hello,

Thanks for the RFC. A few comments.

XPCS_ID
-------
Is 0x00000030 documented for Qualcomm, or is it derived from
NXP_SJA1110_XPCS_ID + 0x10? If it's the latter, it's a magic value and
I'd rather see it confirmed against the Qualcomm documentation or a
register dump from real hardware before it's used for platform
identification.

Non-existent MMDs
-----------------
Returning 0xffff on reads and silently discarding writes is what a
floating bus / unimplemented feature looks like, so I agree with that
direction. My pcs-xpcs-rk does the same.

Structure
---------
pcs-xpcs-plat is itself a platform glue driver, for SoCs that don't
need any platform-specific handling. Adding another abstraction layer
on top of it to cover Qualcomm would be glue on glue. Generic, Qualcomm
and Rockchip differ in power management, address window size (2M vs 8M,
...) and MMD redirection, so they don't share a probe path.

Pushing that into pcs-xpcs-plat would also drag every existing user of
the generic glue along: they would suddenly depend on GENERIC_PHY,
PM_GENERIC_DOMAINS and whatever else the Qualcomm path needs, or they
would have to carry per-platform branches in a driver that is supposed
to be platform-agnostic. A per-SoC-family glue driver, the same way
dwmac-intel, dwmac-rk, dwmac-renesas-gbeth and dwmac-rzn1 are
separate, keeps each integration self-contained and leaves the generic
glue alone.

Would it make sense to take that route here? My pcs-xpcs-rk does the
MMD redirection through a custom MDIO bus; maybe the Qualcomm glue can
reuse that idea directly instead of extending pcs-xpcs-plat. Happy to
help with the generic parts if that's useful.

Best,
Coia