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Date:   Sat, 27 Feb 2021 09:27:54 +0800
From:   Huazhong Tan <>
To:     Andrew Lunn <>
CC:     <>, <>,
        <>, <>, <>,
        Guangbin Huang <>
Subject: Re: [PATCH net] net: phy: fix save wrong speed and duplex problem if
 autoneg is on

On 2021/2/27 8:53, Andrew Lunn wrote:
> On Fri, Feb 26, 2021 at 03:44:42PM +0800, Huazhong Tan wrote:
>> From: Guangbin Huang <>
>> If phy uses generic driver and autoneg is on, enter command
>> "ethtool -s eth0 speed 50" will not change phy speed actually, but
>> command "ethtool eth0" shows speed is 50Mb/s because phydev->speed
>> has been set to 50 and no update later.
>> And duplex setting has same problem too.
>> However, if autoneg is on, phy only changes speed and duplex according to
>> phydev->advertising, but not phydev->speed and phydev->duplex. So in this
>> case, phydev->speed and phydev->duplex don't need to be set in function
>> phy_ethtool_ksettings_set() if autoneg is on.
>> Signed-off-by: Guangbin Huang <>
>> Signed-off-by: Huazhong Tan <>
> I'm not sure, but i think this happens after
> commit 51e2a3846eab18711f4eb59cd0a4c33054e2980a
> Author: Trent Piepho <>
> Date:   Wed Sep 24 10:55:46 2008 +0000
>      PHY: Avoid unnecessary aneg restarts
>      The PHY's aneg is configured and restarted whenever the link is brought up,
>      e.g. when DHCP is started after the kernel has booted.  This can take the
>      link down for several seconds while auto-negotiation is redone.
>      If the advertised features haven't changed, then it shouldn't be necessary
>      to bring down the link and start auto-negotiation over again.
>      genphy_config_advert() is enhanced to return 0 when the advertised features
>      haven't been changed and >0 when they have been.
>      genphy_config_aneg() then uses this information to not call
>      genphy_restart_aneg() if there has been no change.
> Before then, i think autoneg was unconditionally restarted, and so the
> speed would get overwritten when autoneg completed. After this patch,
> since autoneg is not being changed when only speed is set, autoneg is
> not triggered.
> 	Andrew


> .

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