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

[Mohd Ayaan Anwar <mohd.anwar@oss.qualcomm.com>]

On Wed, Sep 23, 2026 at 09:17:44PM +0800, Coia Prant wrote:
> 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.
> 

It's the latter (NXP XPCS ID + 0x10). The Qualcomm hardware returns the
standard XPCS identifier (0x7996ced0) upon reading the 3.2, 3.3
PCS_DEV_ID registers. I tried following a similar approach to the NXP
DSA driver of reporting a synthetic value to bind to the Qualcomm part. 

All this was just to make it work with pcs-xpcs-plat without introducing
a ton of code.

> 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.
> 

I agree with your concerns regarding the glue on glue architecture. I
also don't know if each platform glue should define a custom MDIO bus
with similar logic. Maybe we can have a generic abstraction for it?

I know that Alex had a patch introducing pcs-xpcs-regmap.c [1]. My
original code for this platform actually built on top of it before I
moved to the current implementation.

At least I now know that multiple vendors have an MMIO based XPCS,
albeit with differing MMD redirection mechanisms.

I am going through the pcs-xpcs-rk patch and the eee_clk already stood
out to me. On my board, the PCS link does not come up if the EEE clock
is stopped. Going through the databook, I did find a barebones
explanation of why that might be happening for USXGMII, but I need to
dig more into it.

Thank you for the review.

	Ayaan

[1] https://lore.kernel.org/netdev/20260501155421.3329862-2-elder@riscstar.com/