[PATCH] Close non-keyboard devices on DPMS off

Keith Packard keithp at keithp.com
Sun Oct 6 11:17:13 PDT 2013

Mark Kettenis <mark.kettenis at xs4all.nl> writes:

> Is that really desirable?

It has a couple of benefits -- the first is that touch screens and touch
pads often get input while your laptop screen is closed; this prevents
that from waking up the X server.

The second is that turning off input devices can allow the system to
shut down USB resources and save a bunch of power. I posted the patch so
that we could get measurements of the power savings.

> For me, moving the mouse has always been the most natural way to wake
> up the screen.

Yeah, that's the usual way I wake my machine up as well. However, if you
try this on an OS X machine, you'll find that only the keyboard will
wake the machine up. So, it's not a universal policy at least.

> And I can imagine that touching the screen is the most
> natural way to do it on a device with a touchscreen.  Such devices
> might not even have keyboard.

It's hard to imagine a device without *any* keys, but it's certainly
possible. The trick would be to figure out how to detect this
automatically; my machine lists six "keyboard" devices:

    ↳ Power Button                            	id=6	[slave  keyboard (3)]
    ↳ Power Button                            	id=8	[slave  keyboard (3)]
    ↳ Sleep Button                            	id=9	[slave  keyboard (3)]
    ↳ FaceTime HD Camera (Built-in)           	id=11	[slave  keyboard (3)]
    ↳ Apple Inc. Apple Internal Keyboard / Trackpad	id=12	[slave  keyboard (3)]
    ↳ Video Bus                               	id=7	[slave  keyboard (3)]

I think the interesting part here is the potential for power savings
while the screen is blanked; getting some idea of how much closing the
other devices is worth would be really helpful in figuring out when to
make this choice.

keith.packard at intel.com
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