Re: [PATCH v2 07/10] net: pcs: xpcs: add Rockchip RK3568 platform glue driver

> On Sat, Aug 01, 2026 at 10:22:31PM +0800, Coia Prant wrote:
> > The XPCS block contains four MII ports (0..3), each of which can be
> > routed to GMAC0 or GMAC1 via the pcs-handle property in the MAC node.
> > The hardware maps these ports to different MMDs:
> >   - port 0: MMD 7 (ROCKCHIP_MMD_MII)
> >   - port 1: MMD 2 (ROCKCHIP_MMD_MII1)
> >   - port 2: MMD 3 (ROCKCHIP_MMD_MII2)
> >   - port 3: MMD 4 (ROCKCHIP_MMD_MII3)
>
> Why is port 0 called ROCKCHIP_MMD_MII not ROCKCHIP_MMD_MII0 ?

Hi Andrew,

The naming follows the Rockchip TRM. The hardware documentation refers to
the MMD for the first port as simply "MII" without a numeric suffix, while
the other ports are named "MII1", "MII2", "MII3". I kept the naming
consistent with the TRM to make it easier to cross-reference.

As I understand it, this is probably because the MII controls not only
Port 0, but
also the entire PCS (these registers are read-only in Ports 1-3 and reflected
back to the MII).

If you prefer, I can rename it to ROCKCHIP_MMD_MII0 for consistency. Let me
know and I'll update it in v3.

>
> > +static int xpcs_rk_read_c22(struct mii_bus *bus, int addr, int reg)
> > +{
> > +     struct dw_xpcs_rk *pxpcs = bus->priv;
> > +     int dev;
> > +
> > +     if (!xpcs_rk_mdio_addr_validate(addr))
> > +             return -ENODEV;
> > +
> > +     dev = xpcs_rk_mdio_read_remapping(addr, MDIO_MMD_VEND2, reg);
>
> Does this mean C22 registers are mapped into the first 32 of C45
> MDIO_MMD_VEND2?

Yes, exactly. The C22 register space (reg 0-31) is mapped into the first
32 registers of the VEND2 MMD (MMD 7). This is how the hardware is designed
and matches the standard C22 to C45 address mapping.

>
> > +static int xpcs_rk_read_c45(struct mii_bus *bus, int addr, int dev, int reg)
> > +{
> > +     struct dw_xpcs_rk *pxpcs = bus->priv;
> > +
> > +     if (!xpcs_rk_mdio_addr_validate(addr))
> > +             return -ENODEV;
> > +
> > +     dev = xpcs_rk_mdio_read_remapping(addr, dev, reg);
>
> Should it be returning an error for dev == MDIO_MMD_VEND2? Or at least
> if reg < 32?

No, we cannot simply return an error here. The generic xpcs driver uses
C45 reads to access the VEND2 MMD for various operations, including reading
the device ID (xpcs_read_id). If we returned an error for VEND2 or blocked
reg < 32, the xpcs core driver would fail to identify the device and the
PCS would not work.

The VEND2 MMD is fully accessible on this hardware and contains the
standard C22 registers (0-31) as well as vendor-specific registers.
The remapping function maps the C45 address space to the correct
hardware MMD, and then the read/write functions handle the actual access.
This design matches how other xpcs platform drivers (e.g., pcs-xpcs-plat.c)
handle similar hardware.

For invalid MMIDs (e.g., MDIO_MMD_PCS, MDIO_MMD_VEND1, etc.), the
xpcs_rk_mdio_read_remapping() function returns -ENXIO, which is then
returned as 0xffff (meaning "no link" / "unavailable"). This is the
standard MDIO behavior for unimplemented registers.

Thanks,
Coia