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CPUFREQ(9)                 Kernel Developer's Manual                CPUFREQ(9)

NAME
     cpufreq, cpufreq_register, cpufreq_deregister, cpufreq_suspend,
     cpufreq_resume, cpufreq_get, cpufreq_get_backend, cpufreq_get_state,
     cpufreq_get_state_index, cpufreq_set, cpufreq_set_all -- interface for
     CPU frequency scaling

SYNOPSIS
     #include <sys/cpufreq.h>

     int
     cpufreq_register(struct cpufreq *cf);

     void
     cpufreq_deregister(void);

     void
     cpufreq_suspend(struct cpu_info *ci);

     void
     cpufreq_resume(struct cpu_info *ci);

     uint32_t
     cpufreq_get(struct cpu_info *ci);

     int
     cpufreq_get_backend(struct cpufreq *cf);

     int
     cpufreq_get_state(uint32_t freq, struct cpufreq_state *cfs);

     int
     cpufreq_get_state_index(uint32_t index, struct cpufreq_state *cfs);

     void
     cpufreq_set(struct cpu_info *ci, uint32_t freq);

     void
     cpufreq_set_all(uint32_t freq);

DESCRIPTION
     The machine-independent cpufreq interface provides a framework for CPU
     frequency scaling done by a machine-dependent backend implementation.
     User space control is available via cpuctl(8).

     The cpufreq interface is a per-CPU framework.  It is implicitly assumed
     that the frequency can be set independently for all processors in the
     system.  However, cpufreq does not imply any restrictions upon whether
     this information is utilized by the actual machine-dependent
     implementation.  It is possible to use cpufreq with frequency scaling
     implemented via pci(4).  In addition, it assumed that the available
     frequency levels are shared uniformly by all processors in the system,
     even when it is possible to control the frequency of individual
     processors.

     It should be noted that the cpufreq interface is generally stateless.
     This implies for instance that possible caching should be done in the
     machine-dependent backend.  The cpufreq_suspend() and cpufreq_resume()
     functions are exceptions.  These can be integrated with pmf(9).

FUNCTIONS
     cpufreq_register(cf)
              The cpufreq_register() function initializes the interface by
              associating a machine-dependent backend with the framework.
              Only one backend can be registered.  Upon successful completion,
              cpufreq_register() returns 0 and sets the frequency of all
              processors to the maximum available level.  Note that the
              registration can be done only after interrupts have been
              enabled; cf.  config_interrupts(9).

              The following elements in struct cpufreq should be filled prior
              to the call:

                    char                     cf_name[CPUFREQ_NAME_MAX];
                    struct cpufreq_state     cf_state[CPUFREQ_STATE_MAX];
                    uint32_t                 cf_state_count;
                    bool                     cf_mp;
                    void                    *cf_cookie;
                    xcfunc_t                 cf_get_freq;
                    xcfunc_t                 cf_set_freq;

              o   The name of the backend should be given in cf_name.

              o   The cpufreq_state structure conveys descriptive information
                  about the frequency states.  The following fields can be
                  used for the registration:

                    uint32_t                 cfs_freq;
                    uint32_t                 cfs_power;

                  From these cfs_freq (the clock frequency in MHz) is
                  mandatory, whereas the optional cfs_power can be filled to
                  describe the power consumption (in mW) of each state.  The
                  cf_state array must be filled in descending order, that is,
                  the highest frequency should be at the zero index.

                  If the backend operates with a simple boolean switch without
                  knowing the clock frequencies, the cfs_freq field should be
                  set to CPUFREQ_STATE_ENABLED or CPUFREQ_STATE_DISABLED.  The
                  first constant should precede the latter one in cf_state.

              o   The cf_state_count field defines the number of states that
                  the backend has filled in the cf_state array.

              o   The cf_mp boolean should be set to false if it is known that
                  the backend can not handle per-CPU frequency states; changes
                  should always be propagated to all processors in the system.

              o   The cf_cookie field is an opaque pointer passed to the
                  backend when cpufreq_get(), cpufreq_set(), or
                  cpufreq_set_all() is called.

              o   The cf_get_freq and cf_set_freq are function pointers that
                  should be associated with the machine-dependent functions to
                  get and set a frequency, respectively.  The xcfunc_t type is
                  part of xcall(9).  When the function pointers are invoked by
                  cpufreq, the first parameter is always the cf_cookie and the
                  second parameter is the frequency, defined as uint32_t *.

     cpufreq_deregister()
              Deregisters any possible backend in use.

     cpufreq_suspend(ci)
              The cpufreq_suspend() can be called when the processor suspends.
              The function saves the current frequency of ci and sets the
              minimum available frequency.

     cpufreq_resume(ci)
              Resumes the frequency of ci that was used before suspend.

     cpufreq_get(ci)
              Returns the current frequency of the processor ci.  A value zero
              is returned upon failure.

     cpufreq_get_backend(cf)
              Upon successful completion, cpufreq_get_backend() returns 0 and
              fills cf with the data related to the currently used backend.

     cpufreq_get_state(freq, cfs)
              The cpufreq_get_state() function looks for the given frequency
              from the array of known frequency states.  If freq is not found,
              the closest match is returned.  Upon successful completion, the
              function returns zero and stores the state information to cfs.

     cpufreq_get_state_index(index, cfs)
              Stores the frequency state with the given index to cfs,
              returning zero upon successful completion.

     cpufreq_set(ci, freq)
              The cpufreq_set() function sets the frequency of ci to freq.

     cpufreq_set_all(freq)
              Sets freq for all processors in the system.

     The three functions cpufreq_get(), cpufreq_set(), and cpufreq_set_all()
     guarantee that the call will be made in curcpu(9).  The interface holds a
     mutex(9) while calling the functions.  This, and the use of xcall(9),
     implies that no memory can be allocated in the backend during the calls.
     Nor should the functions be called from interrupt context.

CODE REFERENCES
     The cpufreq interface is implemented within sys/kern/subr_cpufreq.c.

SEE ALSO
     cpuctl(8), pmf(9), xcall(9)

     Venkatesh Pallipadi and Alexey Starikovskiy, The Ondemand Governor. Past,
     Present, and Future, Intel Open Source Technology Center,
     http://www.kernel.org/doc/ols/2006/ols2006v2-pages-223-238.pdf, July,
     2006, Proceedings of the Linux Symposium.

HISTORY
     The cpufreq interface first appeared in NetBSD 6.0.

AUTHORS
     Jukka Ruohonen <jruohonen@iki.fi>

BUGS
     The interface does not support different ``governors'' and policies.

NetBSD 7.1.2                   October 27, 2011                   NetBSD 7.1.2