linux-kernel - Re: phy: fixed link 1000 or 100 set with autoneg off

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Message-ID: <c23dcdb0-f493-453d-82b9-b498f4d3c88b@gmail.com>
Date:   Mon, 23 Oct 2023 09:52:19 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     "Jia, Fang" <fang.jia@...driver.com>, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: phy: fixed link 1000 or 100 set with autoneg off

On 23.10.2023 09:01, Jia, Fang wrote:
> Hi Experts,
> 
> We use NXP LS1046 board and face an issue about the eth interface speed.
> 
> 1) Scenario
> 
> we set fixed link 1000Mb/s in device tree.
> 
> However, after we set the auto-neg off, then the eth1's speed changed to 10M and Duplex changed to Half.
> The value of /sys/class/net/eth1/speed is 10 and /sys/class/net/eth1/duplex is half
> 
Why do you set aneg to off? Leave aneg on, that's the only supported
mode in swphy. 1000Mbps requires aneg anyway per standard.

> 2) Log is as following.
> 
> # ifconfig eth1 up
> # ethtool eth1
> Settings for eth1:
>         Supported ports: [ MII ]
>         Supported link modes:   1000baseT/Full
>         Supported pause frame use: Symmetric Receive-only
>         Supports auto-negotiation: Yes
> 
>         Supported FEC modes: Not reported
> 
>         Advertised link modes:  1000baseT/Full
>         Advertised pause frame use: Symmetric Receive-only
> 
>         Advertised auto-negotiation: Yes
>         Advertised FEC modes: Not reported
>         Speed: 1000Mb/s
>         Duplex: Full
>         Port: MII
>         PHYAD: 1
>         Transceiver: internal
>         Auto-negotiation: on
>         Supports Wake-on: d
>         Wake-on: d
>         Current message level: 0xffffffff (-1)
>                                drv probe link timer ifdown ifup rx_err tx_err tx_queued intr tx_done rx_status pktdata hw wol 0xffff8000
>         Link detected: yes
> 
> # ethtool -s eth1 autoneg off
> # ethtool eth1
> Settings for eth1:
>         Supported ports: [ MII ]
>         Supported link modes:   1000baseT/Full
>         Supported pause frame use: Symmetric Receive-only
>         Supports auto-negotiation: Yes
>         Supported FEC modes: Not reported
>         Advertised link modes:  1000baseT/Full
>         Advertised pause frame use: Symmetric Receive-only
>         Advertised auto-negotiation: No
>         Advertised FEC modes: Not reported
>         Speed: 10Mb/s
>         Duplex: Half
>         Port: MII
>         PHYAD: 1
>         Transceiver: internal
>         Auto-negotiation: off
>         Supports Wake-on: d
>         Wake-on: d
>         Current message level: 0xffffffff (-1)
>                                drv probe link timer ifdown ifup rx_err tx_err tx_queued intr tx_done rx_status pktdata hw wol 0xffff8000
>         Link detected: yes
> 
> 3) After code tracing, we found that:
> 
> phy_state_machine()
>     state PHY_RUNNING: phy_check_link_status()
>         phy_read_status()
>             genphy_read_status()
>                 genphy_read_status_fixed()
> 
> In genphy_read_status_fixed(), the speed and duplex changed.
> It seems like the bmcr value is always 0x1000 from swphy_read_reg().
> 
> After revert the commit 726097d6d6d(net: phy: improve auto-neg emulation in swphy), then the Speed and Duplex shown comes back to 1000M and Full.
> 
> Could you please take a look it ? Can we revert this commit, is there any side impact ?
> 
> Best Regards,
> Fang