netdev - Re: [PATCH v3 net-next] net: phy: realtek: read actual speed on rtl8211f to detect downshift

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Message-ID: <3fdb1d11-d59e-9d3d-a5a8-8f20e4ca7f0a@huawei.com>
Date:   Thu, 26 Nov 2020 09:15:01 +0800
From:   Yonglong Liu <liuyonglong@...wei.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
CC:     Antonio Borneo <antonio.borneo@...com>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, <netdev@...r.kernel.org>,
        Willy Liu <willy.liu@...ltek.com>,
        <linux-kernel@...r.kernel.org>,
        Salil Mehta <salil.mehta@...wei.com>, <linuxarm@...wei.com>,
        <linux-stm32@...md-mailman.stormreply.com>
Subject: Re: [PATCH v3 net-next] net: phy: realtek: read actual speed on
 rtl8211f to detect downshift

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.
>