P-state setting suddenly disappeared, what gives?

[John Baldwin]

On Thursday, November 14, 2013 6:13:43 pm Jung-uk Kim wrote:
> On 2013-11-14 17:41:44 -0500, Adrian Chadd wrote:
> > Hi all,
> >
> > I have this Lenovo T400 that I've been doing FreeBSD development on
> > for a while.
> >
> > It has a P8700 in it:
> >
> > CPU: Intel(R) Core(TM)2 Duo CPU     P8700  @ 2.53GHz (2527.07-MHz
> > 686-class CPU)
> >
> > Now, up until yesterday, ACPI exported the required twiddles to
> > enter various different P-states.
> >
> > However, as of sometime yesterday, it stopped being able to do so.
> >
> > sysctl dev.cpu.0.freq returns nothing. Setting it to something
> > retuns "device not configured." The frequency list (ie, the P-state
> > list) is still fine.
> >
> > I had to load cpufreq.ko to get the enhanced speedstep stuff to
> > show up, but (a) it doesn't support this CPU (and it seems to have
> > stopped growing EST bits after Pentium M CPUs..) and (b) setting
> > the frequency using it versus P-state settings doesn't save as much
> > power.
> >
> > I'd like to try and debug why the heck this is.
> >
> > The laptop still works fine, things are just not as "nice" as they
> > once were.
> >
> > Any ideas? Any suggestions on where to start debugging this?
> 
> SSDT tables for Intel processors are usually dynamic and often times
> additional tables are loaded per _OSC or _PDC. [1]  Basically, we
> advertise our capabilities from sys/dev/acpica/acpi_cpu.c, depending
> on loaded device drivers.  Unfortunately, some times it is too late
> and some SSDTs are not properly loaded.  Also, warm booting from other
> OSes to FreeBSD may cause similar problems.
> 
> To debug the problem, you need to dump DSDT and SSDTs and try to
> understand _OSC (or _PDC), _PCT and _PSS for your system.

Also, the reason that est.c doesn't hardcode tables for modern CPUs is that on 
modern systems the tables are provided by ACPI via the acpi_perf(4) driver.

-- 
John Baldwin