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Subject: Re: [PATCH v3 net-next] net: phy: realtek: read actual speed on
 rtl8211f to detect downshift
To:     Russell King - ARM Linux admin <linux@armlinux.org.uk>
CC:     Antonio Borneo <antonio.borneo@st.com>,
        Andrew Lunn <andrew@lunn.ch>,
        Heiner Kallweit <hkallweit1@gmail.com>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>, <netdev@vger.kernel.org>,
        Willy Liu <willy.liu@realtek.com>,
        <linux-kernel@vger.kernel.org>,
        Salil Mehta <salil.mehta@huawei.com>, <linuxarm@huawei.com>,
        <linux-stm32@st-md-mailman.stormreply.com>
References: <20201124143848.874894-1-antonio.borneo@st.com>
 <20201124230756.887925-1-antonio.borneo@st.com>
 <d62710c3-7813-7506-f209-fcfa65931778@huawei.com>
 <f24476cc-39f0-ea5f-d6af-faad481e3235@huawei.com>
 <20201125170714.GK1551@shell.armlinux.org.uk>
From:   Yonglong Liu <liuyonglong@huawei.com>
Message-ID: <3fdb1d11-d59e-9d3d-a5a8-8f20e4ca7f0a@huawei.com>
Date:   Thu, 26 Nov 2020 09:15:01 +0800
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Hi, Russell:

     I found this message in kernel log, thanks!

On 2020/11/26 1:07, Russell King - ARM Linux admin wrote:
> On Thu, Nov 26, 2020 at 12:57:37AM +0800, Yonglong Liu wrote:
>> Hi, Antonio:
>>
>>      Could you help to provide a downshift warning message when this happen?
>>
>>      It's a little strange that the adv and the lpa support 1000M, but
>> finally the link speed is 100M.
> That is an identifying feature of downshift.
>
> Downshift can happen at either end of the link, and since we must not
> change the "Advertised link modes" since this is what userspace
> configured, if a downshift occurs at the local end, then you will get
> the ethtool output you provide, where the speed does not agree with
> the reported advertisements.
>
> You should already be getting a warning in the kernel log when this
> happens; phy_check_downshift() which is part of the phylib core code
> will check this every time the link comes up. You should already
> have a message "Downshift occurred ..." in your kernel log. Please
> check.
>