315 lines
8.4 KiB
Groff
315 lines
8.4 KiB
Groff
.\" $NetBSD: cpufreq.9,v 1.6 2011/10/27 05:25:08 jruoho Exp $ */
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.\"
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.\" Copyright (c) 2011 Jukka Ruohonen <jruohonen.iki.fi>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\"
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd October 27, 2011
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.Dt CPUFREQ 9
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.Os
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.Sh NAME
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.Nm cpufreq ,
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.Nm cpufreq_register ,
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.Nm cpufreq_deregister ,
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.Nm cpufreq_suspend ,
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.Nm cpufreq_resume ,
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.Nm cpufreq_get ,
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.Nm cpufreq_get_backend ,
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.Nm cpufreq_get_state ,
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.Nm cpufreq_get_state_index ,
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.Nm cpufreq_set ,
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.Nm cpufreq_set_all
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.Nd interface for CPU frequency scaling
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.Sh SYNOPSIS
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.In sys/cpufreq.h
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.Ft int
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.Fn cpufreq_register "struct cpufreq *cf"
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.Ft void
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.Fn cpufreq_deregister "void"
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.Ft void
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.Fn cpufreq_suspend "struct cpu_info *ci"
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.Ft void
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.Fn cpufreq_resume "struct cpu_info *ci"
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.Ft uint32_t
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.Fn cpufreq_get "struct cpu_info *ci"
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.Ft int
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.Fn cpufreq_get_backend "struct cpufreq *cf"
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.Ft int
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.Fn cpufreq_get_state "uint32_t freq" "struct cpufreq_state *cfs"
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.Ft int
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.Fn cpufreq_get_state_index "uint32_t index" "struct cpufreq_state *cfs"
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.Ft void
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.Fn cpufreq_set "struct cpu_info *ci" "uint32_t freq"
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.Ft void
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.Fn cpufreq_set_all "uint32_t freq"
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.\" .Ft void
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.\" .Fn cpufreq_set_higher "struct cpu_info *ci"
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.\" .Ft void
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.\" .Fn cpufreq_set_lower "struct cpu_info *ci"
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.Sh DESCRIPTION
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The machine-independent
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.Nm
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interface provides a framework for
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.Tn CPU
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frequency scaling done by a machine-dependent backend implementation.
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User space control is available via
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.Xr cpuctl 8 .
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.Pp
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The
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.Nm
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interface is a per-CPU framework.
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It is implicitly assumed that the frequency can be set
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independently for all processors in the system.
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However,
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.Nm
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does not imply any restrictions upon whether this information
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is utilized by the actual machine-dependent implementation.
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It is possible to use
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.Nm
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with frequency scaling implemented via
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.Xr pci 4 .
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In addition, it assumed that the available frequency levels are
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shared uniformly by all processors in the system,
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even when it is possible to control the frequency of individual processors.
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.Pp
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It should be noted that the
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.Nm
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interface is generally stateless.
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This implies for instance that possible caching should
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be done in the machine-dependent backend.
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The
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.Fn cpufreq_suspend
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and
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.Fn cpufreq_resume
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functions are exceptions.
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These can be integrated with
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.Xr pmf 9 .
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.Sh FUNCTIONS
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.Bl -tag -width compact
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.It Fn cpufreq_register "cf"
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The
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.Fn cpufreq_register
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function initializes the interface by associating
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a machine-dependent backend with the framework.
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Only one backend can be registered.
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Upon successful completion,
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.Fn cpufreq_register
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returns 0 and sets the frequency of all processors
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to the maximum available level.
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Note that the registration can be done
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only after interrupts have been enabled; cf.
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.Xr config_interrupts 9 .
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.Pp
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The following elements in
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.Vt struct cpufreq
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should be filled prior to the call:
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.Bd -literal -offset indent
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char cf_name[CPUFREQ_NAME_MAX];
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struct cpufreq_state cf_state[CPUFREQ_STATE_MAX];
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uint32_t cf_state_count;
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bool cf_mp;
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void *cf_cookie;
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xcfunc_t cf_get_freq;
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xcfunc_t cf_set_freq;
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.Ed
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.Pp
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.Bl -bullet
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.It
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The name of the backend should be given in
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.Vt cf_name .
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.It
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The
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.Vt cpufreq_state
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structure conveys descriptive information about the frequency states.
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The following fields can be used for the registration:
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.Bd -literal -offset 2n
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uint32_t cfs_freq;
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uint32_t cfs_power;
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.Ed
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.Pp
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From these
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.Vt cfs_freq
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(the clock frequency in MHz) is mandatory, whereas the optional
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.Vt cfs_power
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can be filled to describe the power consumption (in mW) of each state.
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The
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.Fa cf_state
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array must be filled in descending order, that is, the highest
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frequency should be at the zero index.
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.Pp
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If the backend operates with a simple boolean switch
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without knowing the clock frequencies, the
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.Fa cfs_freq
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field should be set to
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.Dv CPUFREQ_STATE_ENABLED
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or
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.Dv CPUFREQ_STATE_DISABLED .
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The first constant should precede the latter one in
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.Vt cf_state .
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.It
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The
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.Vt cf_state_count
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field defines the number of states that the backend has filled in the
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.Vt cf_state
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array.
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.It
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The
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.Vt cf_mp
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boolean should be set to false if it is known that the backend
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can not handle per-CPU frequency states;
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changes should always be propagated
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to all processors in the system.
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.It
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The
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.Vt cf_cookie
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field is an opaque pointer passed to the backend when
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.Fn cpufreq_get ,
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.Fn cpufreq_set ,
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or
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.Fn cpufreq_set_all
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is called.
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.It
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The
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.Vt cf_get_freq
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and
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.Vt cf_set_freq
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are function pointers that should be associated with the
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machine-dependent functions to get and set a frequency, respectively.
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The
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.Vt xcfunc_t
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type is part of
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.Xr xcall 9 .
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When the function pointers are invoked by
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.Nm ,
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the first parameter is always the
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.Vt cf_cookie
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and the second parameter is the frequency, defined as
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.Vt uint32_t * .
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.El
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.It Fn cpufreq_deregister
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Deregisters any possible backend in use.
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.It Fn cpufreq_suspend "ci"
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The
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.Fn cpufreq_suspend
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can be called when the processor suspends.
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The function saves the current frequency of
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.Fa ci
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and sets the minimum available frequency.
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.It Fn cpufreq_resume "ci"
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Resumes the frequency of
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.Fa ci
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that was used before suspend.
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.It Fn cpufreq_get "ci"
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Returns the current frequency of the processor
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.Fa ci .
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A value zero is returned upon failure.
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.It Fn cpufreq_get_backend "cf"
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Upon successful completion,
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.Fn cpufreq_get_backend
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returns 0 and fills
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.Fa cf
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with the data related to the currently used backend.
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.It Fn cpufreq_get_state "freq" "cfs"
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The
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.Fn cpufreq_get_state
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function looks for the given frequency
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from the array of known frequency states.
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If
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.Fa freq
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is not found, the closest match is returned.
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Upon successful completion,
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the function returns zero and stores the state information to
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.Fa cfs .
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.It Fn cpufreq_get_state_index "index" "cfs"
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Stores the frequency state with the given
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.Fa index
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to
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.Fa cfs ,
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returning zero upon successful completion.
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.It Fn cpufreq_set "ci" "freq"
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The
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.Fn cpufreq_set
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function sets the frequency of
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.Fa ci
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to
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.Fa freq .
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.It Fn cpufreq_set_all "freq"
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Sets
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.Fa freq
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for all processors in the system.
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.\" .It Fn cpufreq_set_higher "ci"
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.\" Decrements the current frequency level of
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.\" .Fa ci
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.\" by one state.
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.\" .It Fn cpufreq_set_lower "ci"
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.\" Increases the current frequency state of
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.\" .Fa ci
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.\" by one state.
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.El
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.Pp
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The three functions
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.Fn cpufreq_get ,
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.Fn cpufreq_set ,
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and
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.Fn cpufreq_set_all
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guarantee that the call will be made in
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.Xr curcpu 9 .
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The interface holds a
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.Xr mutex 9
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while calling the functions.
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This, and the use of
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.Xr xcall 9 ,
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implies that no memory can be allocated in the backend during the calls.
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Nor should the functions be called from interrupt context.
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.Sh CODE REFERENCES
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The
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.Nm
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interface is implemented within
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.Pa sys/kern/subr_cpufreq.c .
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.Sh SEE ALSO
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.Xr cpuctl 8 ,
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.Xr pmf 9 ,
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.Xr xcall 9
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.Rs
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.%A Venkatesh Pallipadi
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.%A Alexey Starikovskiy
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.%T The Ondemand Governor. Past, Present, and Future
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.%I Intel Open Source Technology Center
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.%O Proceedings of the Linux Symposium
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.%D July, 2006
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.%U http://www.kernel.org/doc/ols/2006/ols2006v2-pages-223-238.pdf
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.Re
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.Sh HISTORY
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The
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.Nm
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interface first appeared in
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.Nx 6.0 .
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.Sh AUTHORS
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.An Jukka Ruohonen
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.Aq jruohonen@iki.fi
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.Sh BUGS
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The interface does not support different
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.Dq governors
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and policies.
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