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    SubjectRe: [PATCH RFC v1 0/7] net: phy: Ethernet PHY powerdown optimization
    On 11/20/2013 09:36 PM, David Miller wrote:
    > From: Sebastian Hesselbarth <>
    > Date: Wed, 20 Nov 2013 21:21:46 +0100
    >> Ethernet PHYs consume a significant amount of power when link is detected.
    >> Especially, for embedded systems it can be easily 20-40% of total system
    >> power. Now, currently most likely all ethernet drivers leave PHYs powered
    >> on, even if the device is taken down. Also, some stupid boot loaders power
    >> on all PHYs available.
    >> This RFC deals with saving power consumed by ethernet PHYs, that have no
    >> corresponding ethernet device driver or are attached to ethernet devices
    >> which are taken down by user request, i.e. ifconfig ethN down. Ports with
    >> no link, i.e. cable removed, are already quite good at power saving due to
    >> PHY internal link detection.
    > The idea is sound and the goal is of course valuable, but it brings up
    > a chronically reoccurring issue as of late.
    > You cannot reset the PHY or take it down without somehow retaining the
    > settings the PHY had when you bring it back up.

    Right, as far as I understand BMCR powerdown, i.e. what is called in
    genphy_suspend/resume, powers down the PHY but _does_ retain PHY config.
    It is not resetting the device.

    I haven't checked a lot of datasheets but [1] notes that "registers will
    preserve their configuration". Even if we have PHYs that do not preserve
    it, they should have a device specific callback for suspend/resume that
    takes care of preserving it.


    > If I ifdown/ifup a device, my ethtool link configuration better be
    > retained.
    > This means the PHY layer must have a way to reprogram the device when
    > it is brought back up, with whatever settings the software state
    > things are there.

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