netdev - Re: [RFC PATCH net-next 1/8] ethtool: Add ability to control transceiver modules' low power mode

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Message-ID: <20210811060343.014724e8@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 11 Aug 2021 06:03:43 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Ido Schimmel <idosch@...sch.org>
Cc:     Andrew Lunn <andrew@...n.ch>,
        "Keller, Jacob E" <jacob.e.keller@...el.com>,
        netdev@...r.kernel.org, davem@...emloft.net, mkubecek@...e.cz,
        pali@...nel.org, vadimp@...dia.com, mlxsw@...dia.com,
        Ido Schimmel <idosch@...dia.com>
Subject: Re: [RFC PATCH net-next 1/8] ethtool: Add ability to control
 transceiver modules' low power mode

On Wed, 11 Aug 2021 14:33:06 +0300 Ido Schimmel wrote:
> # ethtool --set-module swp13 low-power on
> 
> $ ethtool --show-module swp13
> Module parameters for swp13:
> low-power true
> 
> # ip link set dev swp13 up
> 
> $ ip link show dev swp13
> 127: swp13: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN mode DEFAULT group default qlen 1000
>     link/ether 1c:34:da:18:55:49 brd ff:ff:ff:ff:ff:ff
> 
> $ ip link show dev swp14
> 128: swp14: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc fq_codel state DOWN mode DEFAULT group default qlen 1000
>     link/ether 1c:34:da:18:55:4d brd ff:ff:ff:ff:ff:ff

Oh, so if we set low-power true the carrier will never show up?
I thought Andrew suggested the setting is only taken into account 
when netdev is down. That made so much sense to me I assumed we'll
just go with that. I must have misunderstood.