DragonFly power management stuffs

[Sepherosa Ziehau]

On Thu, Jul 23, 2015 at 5:27 PM, Bob Bishop <rb at gid.co.uk> wrote:
> Hi,
>
>> On 23 Jul 2015, at 02:22, Sepherosa Ziehau <sepherosa at gmail.com> wrote:
>>
>> First of all, I'd like to introduce the major power management
>> stuffs currently available on DragonFly.
>>
>> - ACPI P-state.  It has the proper CPU power domain support.
>> - ACPI C-state.  Unlike other BSDs, on relatively recent Intel CPUs
>>  (the oldest Intel CPU I tested is Sandy Bridge), we don't use I/O
>>  port to enter ACPI C2/C3, instead, we give hint to BIOS that 'native
>>  C2/C3' is supported.  BIOS will send us ACPI C2/C3 to mwait C-states
>>  maps through GAS.
>
> Have you checked why other BSDs don’t do that? Broken BIOSs are all too common.

Well, ACPI C-state had been around for quite a long time; probably no
one is bothered to update it?

And as for broken BIOS, we did notice one on chromebook, i.e. bus
master status check probably is necessary, but BIOS tells us its not
necessary.

Best Regards,
sephe