(Missing) power states of an Atom N455-based netbook

[Andriy Gapon]

on 02/07/2011 23:30 Vitaly Magerya said the following:
> Andriy Gapon <avg at freebsd.org> wrote:
>>>     VDRV: 00 -> 01
>>
>> Looks like this variable should tell if OS has ACPI Video driver, to be precise
>> if _BCL method was invoked at least once.
>> Looks like in your case the driver doesn't attach for some reason?..
> 
> I don't have acpi_video loaded (it's not loaded by default). If I
> do load it, VDRV indeed becomes 1 (brightness controls that acpi_video
> exposes don't work though; this appears to be a known problem with
> Samsung laptops).

This might warrant a separate investigation and a PR if we don't have one already.
Not sure if I could be of help with it, though.

>> Actually, it seems that they have them simply hardcoded:
>> http://lxr.linux.no/#linux+v2.6.39/drivers/idle/intel_idle.c#L171
>> I am not sure how to check on Linux which cpuidle driver is being used.  If you
>> know, could please check that?  And if the driver is intel_idle, then there is
>> no mystery, they use those hardcoded values.
> 
> I think the mystery is solved then:
> 
>     $ cat /sys/devices/system/cpu/cpuidle/current_driver
>     intel_idle

Possible courses of action:

1. Do nothing and leave you with your workaround.

2. Provide intel_idle-like driver for FreeBSD.  I don't like this approach for
reasons I've stated before.

3. Try to make FreeBSD smarter with respect to dynamically changing C-states.  I
think it would be useful if we received a devd notifications about C-state
reconfiguration.  Then we could execute /etc/rc.d/power_profile to account for the
new configuration.

-- 
Andriy Gapon