Re: [PATCH net] net: phy: fix save wrong speed and duplex problem if autoneg is on

[Huazhong Tan]

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 <huangguangbin2@xxxxxxxxxx>
> >
> > 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 <huangguangbin2@xxxxxxxxxx>
> > Signed-off-by: Huazhong Tan <tanhuazhong@xxxxxxxxxx>
> I'm not sure, but i think this happens after
>
> commit 51e2a3846eab18711f4eb59cd0a4c33054e2980a
> Author: Trent Piepho <tpiepho@xxxxxxxxxxxxx>
> 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


Thanks.


> .