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

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Date:   Sat, 27 Feb 2021 09:27:54 +0800
From:   Huazhong Tan <tanhuazhong@...wei.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     <f.fainelli@...il.com>, <hkallweit1@...il.com>,
        <davem@...emloft.net>, <kuba@...nel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Guangbin Huang <huangguangbin2@...wei.com>
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 <huangguangbin2@...wei.com>
>>
>> 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@...wei.com>
>> Signed-off-by: Huazhong Tan <tanhuazhong@...wei.com>
> I'm not sure, but i think this happens after
>
> commit 51e2a3846eab18711f4eb59cd0a4c33054e2980a
> Author: Trent Piepho <tpiepho@...escale.com>
> 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.


> .