Re: [PATCH net] net: phy: qcom: at803x: Use the correct bit to disable extended next page

[Andrew Lunn]

On Fri, Apr 10, 2026 at 07:10:20PM +0200, Maxime Chevallier wrote:
> As noted in the blamed commit, the AR8035 and other PHYs from this
> family advertise the Extended Next Page support by default, which may be
> understood by some partners as this PHY being multi-gig capable.
> 
> The fix is to disable XNP advertising, which is done by setting bit 12
> of the Auto-Negotiation Advertisement Register (MII_ADVERTISE).
> 
> The blamed commit incorrectly uses MDIO_AN_CTRL1_XNP, which is bit 13 as per
> 802.3 : 45.2.7.1 AN control register (Register 7.0)
> 
> BIT 12 in MII_ADVERTISE is wrapped by ADVERTISE_RESV, used by some
> drivers such as the aquantia one. 802.3 Clause 28 defines bit 12 as
> Extended Next Page ability, at least in recent versions of the standard.

> Let's add a define for it and use it in the at803x driver.

I agree with this, it defines the C22 4.12 bit. And this is what the
at803x driver is using it for.

>  static void at803x_link_change_notify(struct phy_device *phydev)
> diff --git a/include/uapi/linux/mii.h b/include/uapi/linux/mii.h
> index 39f7c44baf53..61d6edad4b94 100644
> --- a/include/uapi/linux/mii.h
> +++ b/include/uapi/linux/mii.h
> @@ -82,7 +82,8 @@
>  #define ADVERTISE_100BASE4	0x0200	/* Try for 100mbps 4k packets  */
>  #define ADVERTISE_PAUSE_CAP	0x0400	/* Try for pause               */
>  #define ADVERTISE_PAUSE_ASYM	0x0800	/* Try for asymetric pause     */
> -#define ADVERTISE_RESV		0x1000	/* Unused...                   */
> +#define ADVERTISE_XNP		0x1000  /* Extended Next Page */
> +#define ADVERTISE_RESV		ADVERTISE_XNP /* Used to be reserved */

Should we keep ADVERTISE_RESV?

  45.2.7.6 AN advertisement register

  If the Auto-Negotiation advertisement register (register 4) is
  present, (see 28.2.4.1.3), then this register is a copy of the
  Auto-Negotiation advertisement register (register 4). In this case,
  reads to the AN advertisement register (7.16) report the value of
  the Auto-Negotiation advertisement register (register 4); writes to
  the AN advertisement register (7.16) cause a write to occur to the
  Auto-Negotiation advertisement register.

So MDIO_MMD_AN:MDIO_AN_ADVERTISE is a straight copy of MII_ADVERTISE.

        ef4_mdio_write(efx, MDIO_MMD_AN, MDIO_AN_ADVERTISE, reg);
        ret = phy_write_mmd(phydev, MDIO_MMD_AN, MDIO_AN_ADVERTISE, adv);

So ADVERTISE_XNP is just as valid in the other two drivers using
ADVERTISE_RESV. I think we should change those as well to
ADVERTISE_XNP and remove ADVERTISE_RESV?

	Andrew