On Sat, Dec 17, 2005 at 01:10:33PM -0500, 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. So it seems you're writing a governor. See Documentation/cpu-freq/governors.txt and drivers/cpufreq/cpufreq_conservative.c drivers/cpufreq/cpufreq_ondemand.c drivers/cpufreq/cpufreq_performance.c drivers/cpufreq/cpufreq_powersave.c drivers/cpufreq/cpufreq_userspace.c for a first reference. > 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. of course it does, this is just the sysfs -show function and you're passing it a null pointer as first parameter. If you look at show_available_freqs code you'll see that cpufreq_cpu_data is dereferenced and this happening with interrupts disabled.. hth -- mattia :wq! -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
