DragonFlyBSD

Committed.

Nice! Do the modules have to be loaded (and then unloaded) for this to
take effect or is it enough to just not load them in the first place?

Thanks,
Johannes

It was enough to just not load them even before this patch. Powering down
not used devices at boot time was already there with this commit:

http://leaf.dragonflybsd.org/mailarchive/commits/2008-09/msg00051.html

This patch adds just the ability to power down a devices on module unload.

Ah ok. Is there a way to verify the state of the pci devices?
On my T42 thinkpad I don't see any difference in power consumption
with hw.pci.do_power_nodriver=1 (measured with an external device and
battery removed). I'm always around 20 Watt, with est enabled,
"DynamicClocks" "on" in xorg.conf, and screen backlight set to the
lowest possible value.

Cheers,
Johannes

I use hw.pci.do_power_nodriver=3, btw, but it shouldn't matter much. Is
there unused devices at all? And these devices have to have power
management capabilities, not all PCI devices have these.

I use sysutils/pciutils from pkgsrc to play with PCI configuration space.
It doesn't compile in DragonFly without the patch, pkgsrc bugreport is
there about year or so :(. Take patch is available at [1]. lspci -vvv
shows to you all devices with decoded configuration space. For example
ABOUT my wireless card it shows this:

Capabilities: [40] Power Management version 2
Flags: PMEClk- DSI- D1+ D2- AuxCurrent=375mA
PME
Status: D3 PME-Enable- DSel=0 DScale=0 PME-

Important bit is "Status: D3" - ie. this device is powered down.

[1] -
http://leaf.dragonflybsd.org/~hasso/pkgsrc-patches/pkgsrc-sysutils-pciutils.patch

lspci -vv indeed shows some devices (usb controller, sound card, ethernet card,
and modem) in D3 state.

Thanks,
Johannes