netdev - Re: Cutting the link on ndo_stop - phy_stop or phy

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Date:   Wed, 5 Jun 2019 02:03:19 +0300
From:   Vladimir Oltean <olteanv@...il.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Heiner Kallweit <hkallweit1@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Ioana Ciornei <ioana.ciornei@....com>
Subject: Re: Cutting the link on ndo_stop - phy_stop or phy_disconnect?

On Wed, 5 Jun 2019 at 01:59, Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
>
> On Wed, Jun 05, 2019 at 01:44:08AM +0300, Vladimir Oltean wrote:
> > You caught me.
> >
> > But even ignoring the NIC case, isn't the PHY state machine
> > inconsistent with itself? It is ok with callink phy_suspend upon
> > ndo_stop, but it won't call phy_suspend after phy_connect, when the
> > netdev is implicitly stopped?
>
> The PHY state machine isn't inconsistent with itself, but it does
> have strange behaviour.
>
> When the PHY is attached, the PHY is resumed and the state machine
> is in PHY_READY state.  If it goes through a start/stop cycle, the
> state machine transitions to PHY_HALTED and attempts to place the
> PHY into a low power state.  So the PHY state is consistent with
> the state machine state (we don't end up in the same state but with
> the PHY in a different state.)
>
> What we do have is a difference between the PHY state (and state
> machine state) between the boot scenario, and the interface up/down
> scenario, the latter behaviour having been introduced by a commit
> back in 2013:
>
>     net: phy: suspend phydev when going to HALTED
>
>     When phydev is going to HALTED state, we can try to suspend it to
>     safe more power. phy_suspend helper will check if PHY can be suspended,
>     so just call it when entering HALTED state.
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up
> According to speedtest.net: 11.9Mbps down 500kbps up

I am really not into the PHYLIB internals, but basically what you're
telling me is that running "ip link set dev eth0 down" is a
stronger/more imperative condition than not running "ip link set dev
eth0 up"... Does it also suspend the PHY if I put the interface down
while it was already down?

-Vladimir