Re: writing a cpufreq driver

[Dave Jones <davej@redhat.com>]

On Thu, Sep 21, 2006 at 01:48:33PM -0500, Ryan Underwood wrote:
 > 
 > I wrote a cpufreq target driver for older Toshiba laptops.  It uses SMM
 > to change between a "fast" and a "slow" processing speed.  I have two
 > remaining bugs.  Any comments would be appreciated.
 > 
 > 1.  The first time cpufreq changes speed, I get the whole "Losing some
 > ticks... checking if CPU frequency changed." then eventually "Losing too
 > many ticks!" and timer switches to PIT.  This does not happen when I use
 > the /dev/toshiba driver to change speeds from userspace.  Not sure what
 > is going on here...  SMI handler latency is between 6 and 7 ms.

Is loops_per_jiffy being correctly scaled on a speed transition?
Hmm, powernow-k7.c seems to be the only driver that's calling recalibrate_cpu_khz()

 > 2.  The current CPU frequency is stored in NVRAM by the SMI handler.

Wow, that's umm, crap :-}

 > Unfortunately, this means if cpufreq throttles the CPU and the system is
 > then rebooted, the boot process is exceedingly slow.  Is there some sane
 > way to hook into the shutdown process to restore the appropriate values,
 > or is this something I have to live with?

See register_reboot_notifier()

	Dave