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

Vitaly Magerya vmagerya at gmail.com
Sat Jun 25 15:47:17 UTC 2011

Andriy Gapon <avg at freebsd.org> wrote:
> on 24/06/2011 22:13 Vitaly Magerya said the following:
>> Right after I start the laptop I only see one supported power state:
>>     # sysctl dev.cpu.0.cx_supported
>>     dev.cpu.0.cx_supported: C1/1
>> But after 4+ minutes of uptime more power states kick in:
>>     # sysctl dev.cpu.0.cx_supported
>>     dev.cpu.0.cx_supported: C1/1 C2/20 C3/100
>> I'd like to have all Cx right after the boot. Is this possible?
>> (The temporary solution I employ is to update hw.acpi.cpu.cx_lowest
>> every time devd gets ACPI CMBAT message; this appears to happen
>> right after cx_supported is updated).
> Hmm, strange...
> Can you check if FreeBSD thinks that the system is on AC power until that
> CMBAT message?  (I see in dmesg that during that boot it detected AC as
> disconnected).

AC was indeed disconnected during that boot (and hw.acpi.acline was
0 as expected). If I boot with power on the problem is the same:
about 4 minutes there's only C1, after that there are C1 and C2 (C3
kicks in too once I disable the power).

(I boot with power cord disconnected, since LCD brightness controls
on the laptop don't work with FreeBSD, so that's the only way to
turn the brightness down).

>> Also, when I boot the same machine under Linux (latest Ubuntu),
>> powertop reports C1, C2 and C4 right away. Is it possible to get
>> C4 under FreeBSD as well?
> I believe that what FreeBSD reports as C3 is the same as what Linux reports
> as C4.

The problem is that on Linux power consumption is 5.2W (without USB
suspension or any other things powertop suggests), while on FreeBSD
I'm seeing 6.8W with C3. I assumed this was due to C4/C3 difference,
but maybe Linux is doing something differently.

>> Other ACPI problems, which I have are:
>> 1. When the power cord is plugged in, C3 state disappears.
> Does the same happen with Linux?
> Many notebooks disable deep Cx states when on AC power for some reason.

No. On Linux C4 is reported both with and without AC plugged in.

>> 2. When I plug (or unplug) the power cord I get these two messages:
>>    ACPI Error: [\\_SB_.VDRV] Namespace lookup failure, AE_NOT_FOUND
>>    (20101013/psargs-464) ACPI Error: Method parse/execution failed
>>    [\\_SB_.PCI0.LPC0.H_EC._Q51] (Node 0xc42ac1e0), AE_NOT_FOUND
>>    (20101013/psparse-633)
>>    (This appears to be harmless).
> Not sure about these, looks like some additional/external table is not
> loaded. You may check if the same happens with the latest ACPICA in FreeBSD

I just tried it with CURRENT snapshot from 2011-05-12; it behaves
the same.

(For the record, Linux reports similar messages).

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