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

[Maxime Chevallier]

Hi Andrew,

On 11/04/2026 16:10, Andrew Lunn wrote:
> 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

I agree with that yes and I've considered converting these drivers once
we have net merged into net-next should this patch be applied :)

That said, ADVERTISE_RESV is in uapi, is it even possible to remove it ?

I think the best we can hope for is to no longer have in-tree users of
ADVERTISE_RESV :(

Maxime