Re: Help: Using cpufreq from kernel level

[Robert Hancock <hancockr@shaw.ca>]

Claudio Scordino wrote:
> Hi all,
> 
>    I'm writing a kernel module that needs to get info about the available 
> frequencies on the current processor and to periodically change the current 
> frequency.
> 
> At user level it can be done through
> 
> /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
> /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
> /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed
> 
> but I have no idea how to implement it at kernel level. 
> 
> I tried to declare
> 
> extern struct cpufreq_driver    *cpufreq_driver;
> extern struct cpufreq_policy    *cpufreq_cpu_data[NR_CPUS];
> extern spinlock_t cpufreq_driver_lock;
> extern ssize_t show_available_freqs (struct cpufreq_policy *policy, char 
> *buf);
> 
> and to do
> 
> char buffer [100000] = "\n";
> spin_lock_irqsave(&cpufreq_driver_lock, flags);
> show_available_freqs(cpufreq_cpu_data[0], buffer);
> spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
> 
> but it crashes the system.
> 
> Please, can somebody tell me how this can be done ?

For one thing, you cannot put such a huge buffer on the kernel stack.

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Robert Hancock      Saskatoon, SK, Canada
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