| Date | Wed, 20 Nov 2013 15:36:42 -0500 (EST) | Subject | Re: [PATCH RFC v1 0/7] net: phy: Ethernet PHY powerdown optimization | From | David Miller <> |
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From: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com> 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.
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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