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

[Patrick Oppenlander]

Hi Prashanth,

thank you for addressing the bug. I will test your patch on our
hardware next week.

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>
> ---
>  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
>