Re: writing a cpufreq driver

[Ryan Underwood <nemesis@icequake.net>]

On Thu, Sep 21, 2006 at 03:31:41PM -0400, Dave Jones wrote:
>  > 
>  > 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?

No, because only the firmware knows what the real CPU speeds are.  How
would I deal with this?

>  > 2.  The current CPU frequency is stored in NVRAM by the SMI handler.
> 
> Wow, that's umm, crap :-}

Yup

>  > 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()

That should do it. Thanks!

-- 
Ryan Underwood, <nemesis@icequake.net>