linux-kernel - Re: How to power gate a specific single device from outside?

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Date:   Wed, 25 Oct 2017 00:56:35 +0100
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Waldemar Rymarkiewicz <waldemar.rymarkiewicz@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: How to power gate a specific single device from outside?

> I could not find anything standard that let me power gate single
> device from userland. Perhaps it's considered as a too risky operation
> to expose to the user. I don't want to touch drivers too much as well
> not to make them dependant on extra system feature. Better to have a
> separate module that handles this system mode and forces some drivers
> to unload/power gate their HW.
> 
> Are there already some proven solutions/ideas around the kernel that
> can be used straight away?

For a lot of devices if you close it then it will try and put the device
into a low power state. If a driver isn't doing that then (unless there
are hardware constraints preventing it) it would make sense to fix it.

There are some things entirely in your control - big ones. In particular
the brightness of laptop panels, pulling everything off one CPU socket,
disabling the nmi watchdog, hard disk power settings, stopping processes
that wake up a lot.

Many of those you can set anyway for best power behaviour (see powertop).

Alan