Re: [PATCH net] amd-xgbe: fix MAC_AUTO_SW handling in CL37 AN

[Patrick Oppenlander]

On Fri, 10 Jul 2026 at 09:16, Patrick Oppenlander
<patrick.oppenlander@xxxxxxxxx> wrote:
>
> Hi Prashanth,
>
> thank you for addressing the bug. I will test your patch on our
> hardware next week.

Tested working on 7.0.1 with your patch applied. Thank you.

Patrick

> On Thu, 9 Jul 2026 at 19:50, Prashanth Kumar KR
> <prashanthkumar.k.r@xxxxxxx> wrote:
> >
> > From: Prashanth Kumar KR <PrashanthKumar.K.R@xxxxxxx>
> >
> > MAC_AUTO_SW (VR_MII_DIG_CTRL1 bit 9) enables automatic XPCS speed
> > mode switching after CL37 auto-negotiation and is only meaningful in
> > SGMII MAC mode. The original code unconditionally set this bit on
> > every call to xgbe_an37_set(), including when called from
> > xgbe_an37_disable() with enable=false. This left MAC_AUTO_SW=1 after
> > AN was disabled, causing the XPCS to autonomously switch speed from
> > stale AN state during subsequent mode changes, breaking SGMII speed
> > negotiation on 1G copper SFP modules.
>
> In my testing this was breaking negotiation for all 1G SFP modules,
> not just copper modules.
>
> Patrick
>
> > Fixes: 42fd432fe6d3 ("amd-xgbe: align CL37 AN sequence as per databook")
> > Reported-by: Patrick Oppenlander <patrick.oppenlander@xxxxxxxxx>
> > Link: https://lore.kernel.org/netdev/CAEg67GmFS0Q4oSZkz8zWdOzckSth9_vBPiOy6a7-d697C2w2Xg@xxxxxxxxxxxxxx
> > Signed-off-by: Prashanth Kumar KR <PrashanthKumar.K.R@xxxxxxx>

Tested-by: Patrick Oppenlander <patrick.oppenlander@xxxxxxxxx>

> > ---
> >  drivers/net/ethernet/amd/xgbe/xgbe-mdio.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c b/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
> > index fa0df6181207..12770af031eb 100644
> > --- a/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
> > +++ b/drivers/net/ethernet/amd/xgbe/xgbe-mdio.c
> > @@ -267,9 +267,14 @@ static void xgbe_an37_set(struct xgbe_prv_data *pdata, bool enable,
> >
> >         XMDIO_WRITE(pdata, MDIO_MMD_VEND2, MDIO_CTRL1, reg);
> >
> > -       reg = XMDIO_READ(pdata, MDIO_MMD_VEND2, MDIO_PCS_DIG_CTRL);
> > -       reg |= XGBE_VEND2_MAC_AUTO_SW;
> > -       XMDIO_WRITE(pdata, MDIO_MMD_VEND2, MDIO_PCS_DIG_CTRL, reg);
> > +       if (pdata->an_mode == XGBE_AN_MODE_CL37_SGMII) {
> > +               reg = XMDIO_READ(pdata, MDIO_MMD_VEND2, MDIO_PCS_DIG_CTRL);
> > +               if (enable)
> > +                       reg |= XGBE_VEND2_MAC_AUTO_SW;
> > +               else
> > +                       reg &= ~XGBE_VEND2_MAC_AUTO_SW;
> > +               XMDIO_WRITE(pdata, MDIO_MMD_VEND2, MDIO_PCS_DIG_CTRL, reg);
> > +       }
> >  }
> >
> >  static void xgbe_an37_restart(struct xgbe_prv_data *pdata)
> > --
> > 2.34.1
> >