Re: [PATCH 1/3] net: stmmac: support low-speed USXGMII validation

On Wed, Sep 23, 2026 at 9:09 PM Andrew Lunn [off-list ref] wrote:

quoted

The XPCS also consumes the PHY-generated Clause 37 in-band link and
speed status, so USXGMII must use in-band signalling.

Is this a qualcomm specific feature, or defined in the databook of the
licensed IP.

This is defined by the Synopsys DWC XPCS databook, rather than being
  Qualcomm-specific. The Clause 37 USXGMII implementation added by this
  series uses PHY-generated in-band status containing link, speed and
  duplex information.

quoted

      case DW_AN_C37_USXGMII:
-             return LINK_INBAND_DISABLE;
+             /* The PCS consumes the PHY's CL37 in-band link and speed status. */
+             return LINK_INBAND_ENABLE;

I ask, because when i look at this, i immediately think is this a
behaviour change? Is it going to break existing systems? Or was the
old code broken?

 DW_AN_C37_USXGMII is newly introduced by this series. This change adds
  a separate case for that new mode and leaves the existing DW_10GBASER
  and DW_2500BASEX cases returning LINK_INBAND_DISABLE. Therefore, it
  does not change the behaviour of any existing XPCS mode or system. It
  also matches the implementation added by this series, which enables
  Clause 37 AN and reads the received USXGMII status in
  xpcs_get_state_c37_usxgmii().

        case DW_10GBASER:
        case DW_2500BASEX:
                return LINK_INBAND_DISABLE;

+       case DW_AN_C37_USXGMII:
+               /* The PCS consumes the PHY's CL37 in-band link and
speed status. */
+               return LINK_INBAND_ENABLE;
+

The commit message is where you try to guess what reviewers are going
to ask, and answer the question before they ask. Seeing such answers
in the commit message gives me a good idea you have done your due
diligence, and the patch is probably O.K. Without such comments, i
have to assume this is poor quality code and really exam it in detail.

Thanks for the guidance.

Thanks