[PATCH] cpufreq (5/5): update documentation

update CPUfreq documentation, and move it to extra directory.

Documentation/00-INDEX

@@ -56,6 +56,8 @@ computone.txt
 	- info on Computone Intelliport II/Plus Multiport Serial Driver
 cpqarray.txt
 	- info on using Compaq's SMART2 Intelligent Disk Array Controllers.
+cpufreq/
+	- info on CPU frequency and voltage scaling
 cris/
 	- directory with info about Linux on CRIS architecture.
 devices.txt

Documentation/cpu-freq/core.txt

+     CPU frequency and voltage scaling code in the Linux(TM) kernel
+
+
+		         L i n u x    C P U F r e q
+
+			  C P U F r e q    C o r e
+
+
+		    Dominik Brodowski  <linux@brodo.de>
+		     David Kimdon <dwhedon@debian.org>
+
+
+
+   Clock scaling allows you to change the clock speed of the CPUs on the
+    fly. This is a nice method to save battery power, because the lower
+            the clock speed, the less power the CPU consumes.
+
+
+Contents:
+---------
+1.  CPUFreq core and interfaces
+2.  CPUFreq notifiers
+
+1. General Information
+=======================
+
+The CPUFreq core code is located in linux/kernel/cpufreq.c. This
+cpufreq code offers a standardized interface for the CPUFreq
+architecture drivers (those pieces of code that do actual
+frequency transitions), as well as to "notifiers". These are device
+drivers or other part of the kernel that need to be informed of
+policy changes (ex. thermal modules like ACPI) or of all
+frequency changes (ex. timing code) or even need to force certain
+speed limits (like LCD drivers on ARM architecture). Additionally, the
+kernel "constant" loops_per_jiffy is updated on frequency changes
+here.
+
+
+2. CPUFreq notifiers
+====================
+
+CPUFreq notifiers conform to the standard kernel notifier interface.
+See linux/include/linux/notifier.h for details on notifiers.
+
+There are two different CPUFreq notifiers - policy notifiers and
+transition notifiers.
+
+
+2.1 CPUFreq policy notifiers
+----------------------------
+
+These are notified when a new policy is intended to be set. Each
+CPUFreq policy notifier is called three times for a policy transition:
+
+1.) During CPUFREQ_ADJUST all CPUFreq notifiers may change the limit if
+    they see a need for this - may it be thermal considerations or
+    hardware limitations.
+
+2.) During CPUFREQ_INCOMPATIBLE only changes may be done in order to avoid
+    hardware failure.
+
+3.) And during CPUFREQ_NOTIFY all notifiers are informed of the new policy
+   - if two hardware drivers failed to agree on a new policy before this
+   stage, the incompatible hardware shall be shut down, and the user
+   informed of this.
+
+The phase is specified in the second argument to the notifier.
+
+The third argument, a void *pointer, points to a struct cpufreq_policy
+consisting of five values: cpu, min, max, policy and max_cpu_freq. min 
+and max are the lower and upper frequencies (in kHz) of the new
+policy, policy the new policy, cpu the number of the affected CPU or
+CPUFREQ_ALL_CPUS for all CPUs; and max_cpu_freq the maximum supported
+CPU frequency. This value is given for informational purposes only.
+
+
+2.2 CPUFreq transition notifiers
+--------------------------------
+
+These are notified twice when the CPUfreq driver switches the CPU core
+frequency and this change has any external implications.
+
+The second argument specifies the phase - CPUFREQ_PRECHANGE or
+CPUFREQ_POSTCHANGE.
+
+The third argument is a struct cpufreq_freqs with the following
+values:
+cpu	- number of the affected CPU or CPUFREQ_ALL_CPUS
+old	- old frequency
+new	- new frequency

Documentation/cpu-freq/cpu-drivers.txt

+     CPU frequency and voltage scaling code in the Linux(TM) kernel
+
+
+		         L i n u x    C P U F r e q
+
+			   C P U   D r i v e r s 
+
+		       - information for developers -
+
+
+		    Dominik Brodowski  <linux@brodo.de>
+
+
+
+   Clock scaling allows you to change the clock speed of the CPUs on the
+    fly. This is a nice method to save battery power, because the lower
+            the clock speed, the less power the CPU consumes.
+
+
+Contents:
+---------
+1.   What To Do?
+1.1  Initialization
+1.2  Per-CPU Initialization
+1.3  verify
+1.4  target or setpolicy?
+1.5  target
+1.6  setpolicy
+2.   Frequency Table Helpers
+
+
+
+1. What To Do?
+==============
+
+So, you just got a brand-new CPU / chipset with datasheets and want to
+add cpufreq support for this CPU / chipset? Great. Here are some hints
+on what is neccessary:
+
+
+1.1 Initialization
+------------------
+
+First of all, in an __initcall level 7 or later (preferrably
+module_init() so that your driver is modularized) function check
+whether this kernel runs on the right CPU and the right chipset. If
+so, register a struct cpufreq_driver with the CPUfreq core using
+cpufreq_register_driver()
+
+What shall this struct cpufreq_driver contain? 
+
+cpufreq_driver.name -		The name of this driver.
+
+cpufreq_driver.init -		A pointer to the per-CPU initialization 
+				function.
+
+cpufreq_driver.verify -		A pointer to a "verfication" funciton.
+
+cpufreq_driver.setpolicy _or_ 
+cpufreq_driver.target -		See below on the differences.
+
+And optionally
+
+cpufreq_driver.exit -		A pointer to a per-CPU cleanup function.
+
+
+
+1.2 Per-CPU Initialization
+--------------------------
+
+Whenever a new CPU is registered with the device model, or after the
+cpufreq driver registers itself, the per-CPU initialization fucntion 
+cpufreq_driver.init is called. It takes a struct cpufreq_policy
+*policy as argument. What to do now?
+
+If necessary, activate the CPUfreq support on your CPU (unlock that
+register etc.).
+
+Then, the driver must fill in the following values:
+
+policy->cpuinfo.min_freq _and_
+policy->cpuinfo.max_freq -	the minimum and maximum frequency 
+				(in kHz) which is supported by 
+				this CPU
+policy->cpuinfo.transition_latency   the time it takes on this CPU to
+				switch between two frequencies (if
+				appropriate, else specify
+				CPUFREQ_ETERNAL)
+
+policy->cur			The current operating frequency of
+				this CPU (if appropriate)
+policy->min, 
+policy->max, 
+policy->policy and, if neccessary,
+policy->governor		must contain the "default policy" for
+				this CPU. A few moments later,
+				cpufreq_driver.verify and either
+				cpufreq_driver.setpolicy or
+				cpufreq_driver.target is called with
+				these values.
+
+For setting some of these values, the frequency table helpers might be
+helpful. See the section 2 for more information on them.
+
+
+1.3 verify
+------------
+
+When the user decides a new policy (consisting of
+"policy,governor,min,max") shall be set, this policy must be validated
+so that incompatible values can be corrected. For verifying these
+values, a frequency table helper and/or the
+cpufreq_verify_within_limits(struct cpufreq_policy *policy, unsigned
+int min_freq, unsigned int max_freq) function might be helpful. See
+section 2 for details on frequency table helpers.
+
+You need to make sure that at least one valid frequency (or operating
+range) is within policy->min and policy->max. If necessary, increase
+policy->max fist, and only if this is no solution, decreas policy->min.
+
+
+1.4 target or setpolicy?
+----------------------------
+
+Most cpufreq drivers or even most cpu frequency scaling algorithms 
+only allow the CPU to be set to one frequency. For these, you use the
+->target call.
+
+Some cpufreq-capable processors switch the frequency between certain
+limits on their own. These shall use the ->setpolicy call
+
+
+1.4. target
+-------------
+
+The target call has three arguments: struct cpufreq_policy *policy,
+unsigned int target_frequency, unsigned int relation.
+
+The CPUfreq driver must set the new frequency when called here. The
+actual frequency must be determined using the following rules:
+
+- keep close to "target_freq"
+- policy->min <= new_freq <= policy->max (THIS MUST BE VALID!!!)
+- if relation==CPUFREQ_REL_L, try to select a new_freq higher than or equal
+  target_freq. ("L for lowest, but no lower than")
+- if relation==CPUFREQ_REL_H, try to select a new_freq lower than or equal
+  target_freq. ("H for highest, but no higher than")
+
+Here again the frequency table helper might assist you - see section 3
+for details.
+
+
+1.5 setpolicy
+---------------
+
+The setpolicy call only takes a struct cpufreq_policy *policy as
+argument. You need to set the lower limit of the in-processor or
+in-chipset dynamic frequency switching to policy->min, the upper limit
+to policy->max, and -if supported- select a performance-oriented
+setting when policy->policy is CPUFREQ_POLICY_PERFORMANCE, and a
+powersaving-oriented setting when CPUFREQ_POLICY_POWERSAVE. Also check
+the reference implementation in arch/i386/kernel/cpu/cpufreq/longrun.c
+
+
+
+2. Frequency Table Helpers
+==========================
+
+As most cpufreq processors only allow for being set to a few specific
+frequencies, a "frequency table" with some functions might assist in
+some work of the processor driver. Such a "frequency table" consists
+of an array of struct cpufreq_freq_table entries, with any value in
+"index" you want to use, and the corresponding frequency in
+"frequency". At the end of the table, you need to add a
+cpufreq_freq_table entry with frequency set to CPUFREQ_TABLE_END. And
+if you want to skip one entry in the table, set the frequency to 
+CPUFREQ_ENTRY_INVALID. The entries don't need to be in ascending
+order.
+
+By calling cpufreq_frequency_table_cpuinfo(struct cpufreq_policy *policy,
+					struct cpufreq_frequency_table *table);
+the cpuinfo.min_freq and cpuinfo.max_freq values are detected, and
+policy->min and policy->max are set to the same values. This is
+helpful for the per-CPU initialization stage.
+
+int cpufreq_frequency_table_verify(struct cpufreq_policy *policy,
+                                   struct cpufreq_frequency_table *table);
+assures that at least one valid frequency is within policy->min and
+policy->max, and all other criteria are met. This is helpful for the
+->verify call.
+
+int cpufreq_frequency_table_target(struct cpufreq_policy *policy,
+                                   struct cpufreq_frequency_table *table,
+                                   unsigned int target_freq,
+                                   unsigned int relation,
+                                   unsigned int *index);
+
+is the corresponding frequency table helper for the ->target
+stage. Just pass the values to this function, and the unsigned int
+index returns the number of the frequency table entry which contains
+the frequency the CPU shall be set to. PLEASE NOTE: This is not the
+"index" which is in this cpufreq_table_entry.index, but instead
+cpufreq_table[index]. So, the new frequency is
+cpufreq_table[index].frequency, and the value you stored into the
+frequency table "index" field is
+cpufreq_table[index].index.
+

Documentation/cpu-freq/governors.txt

+     CPU frequency and voltage scaling code in the Linux(TM) kernel
+
+
+		         L i n u x    C P U F r e q
+
+		      C P U F r e q   G o v e r n o r s
+
+		   - information for users and developers -
+
+
+		    Dominik Brodowski  <linux@brodo.de>
+
+
+
+   Clock scaling allows you to change the clock speed of the CPUs on the
+    fly. This is a nice method to save battery power, because the lower
+            the clock speed, the less power the CPU consumes.
+
+
+Contents:
+---------
+1.   What is a CPUFreq Governor?
+
+2.   Governors In the Linux Kernel
+2.1  Performance
+2.2  Powersave
+2.3  Userspace
+
+3.   The Governor Interface in the CPUfreq Core
+
+
+
+1. What Is A CPUFreq Governor?
+==============================
+
+Most cpufreq drivers (in fact, all except one, longrun) or even most
+cpu frequency scaling algorithms only offer the CPU to be set to one
+frequency. In order to offer dynamic frequency scaling, the cpufreq
+core must be able to tell these drivers of a "target frequency". So
+these specific drivers will be transformed to offer a "->target"
+call instead of the existing "->setpolicy" call. For "longrun", all
+stays the same, though.
+
+How to decide what frequency within the CPUfreq policy should be used?
+That's done using "cpufreq governors". Two are already in this patch
+-- they're the already existing "powersave" and "performance" which
+set the frequency statically to the lowest or highest frequency,
+respectively. At least two more such governors will be ready for
+addition in the near future, but likely many more as there are various
+different theories and models about dynamic frequency scaling
+around. Using such a generic interface as cpufreq offers to scaling
+governors, these can be tested extensively, and the best one can be
+selected for each specific use.
+
+Basically, it's the following flow graph:
+
+CPU can be set to switch independetly	 |	   CPU can only be set
+      within specific "limits"		 |       to specific frequencies
+
+                                 "CPUfreq policy"
+		consists of frequency limits (policy->{min,max})
+  		     and CPUfreq governor to be used
+			 /		      \
+			/		       \
+		       /		       the cpufreq governor decides
+		      /			       (dynamically or statically)
+		     /			       what target_freq to set within
+		    /			       the limits of policy->{min,max}
+		   /			            \
+		  /				     \
+	Using the ->setpolicy call,		 Using the ->target call,
+	    the limits and the			  the frequency closest
+	     "policy" is set.			  to target_freq is set.
+						  It is assured that it
+						  is within policy->{min,max}
+
+
+2. Governors In the Linux Kernel
+================================
+
+2.1 Performance
+---------------
+
+The CPUfreq governor "performance" sets the CPU statically to the
+highest frequency within the borders of scaling_min_freq and
+scaling_max_freq.
+
+
+2.1 Powersave
+-------------
+
+The CPUfreq governor "powersave" sets the CPU statically to the
+lowest frequency within the borders of scaling_min_freq and
+scaling_max_freq.
+
+
+2.2 Userspace
+-------------
+
+The CPUfreq governor "userspace" allows the user, or any userspace
+program running with UID "root", to set the CPU to a specifc frequency
+by making a sysfs file "scaling_setspeed" available in the CPU-device
+directory.
+
+
+
+3. The Governor Interface in the CPUfreq Core
+=============================================
+
+A new governor must register itself with the CPUfreq core using
+"cpufreq_register_governor". The struct cpufreq_governor, which has to
+be passed to that function, must contain the following values:
+
+governor->name -	    A unique name for this governor
+governor->governor -	    The governor callback function
+governor->owner	-	    .THIS_MODULE for the governor module (if 
+			    appropriate)
+
+The governor->governor callback is called with the current (or to-be-set)
+cpufreq_policy struct for that CPU, and an unsigned int event. The
+following events are currently defined:
+
+CPUFREQ_GOV_START:   This governor shall start its duty for the CPU
+		     policy->cpu
+CPUFREQ_GOV_STOP:    This governor shall end its duty for the CPU
+		     policy->cpu
+CPUFREQ_GOV_LIMITS:  The limits for CPU policy->cpu have changed to
+		     policy->min and policy->max.
+
+If you need other "events" externally of your driver, _only_ use the
+cpufreq_governor_l(unsigned int cpu, unsigned int event) call to the
+CPUfreq core to ensure proper locking.
+
+
+The CPUfreq governor may call the CPU processor driver using one of
+these two functions:
+
+inline int cpufreq_driver_target(struct cpufreq_policy *policy,
+                                 unsigned int target_freq,
+                                 unsigned int relation);
+
+inline int cpufreq_driver_target_l(struct cpufreq_policy *policy,
+                                   unsigned int target_freq,
+                                   unsigned int relation);
+
+target_freq must be within policy->min and policy->max, of course.
+What's the difference between these two functions? When your governor
+still is in a direct code path of a call to governor->governor, the
+cpufreq_driver_sem lock is still held in the cpufreq core, and there's
+no need to lock it again (in fact, this would cause a deadlock). So
+use cpufreq_driver_target only in these cases. In all other cases (for
+example, when there's a "daemonized" function that wakes up every
+second), use cpufreq_driver_target_l to lock the cpufreq_driver_sem
+before the command is passed to the cpufreq processor driver.
+

Documentation/cpu-freq/index.txt

+     CPU frequency and voltage scaling code in the Linux(TM) kernel
+
+
+		         L i n u x    C P U F r e q
+
+
+
+
+		    Dominik Brodowski  <linux@brodo.de>
+
+
+
+   Clock scaling allows you to change the clock speed of the CPUs on the
+    fly. This is a nice method to save battery power, because the lower
+            the clock speed, the less power the CPU consumes.
+
+
+
+Documents in this directory:
+----------------------------
+core.txt	-	General description of the CPUFreq core and
+			of CPUFreq notifiers
+
+cpu-drivers.txt -	How to implement a new cpufreq processor driver
+
+governors.txt	-	What are cpufreq governors and how to
+			implement them?
+
+index.txt	-	File index, Mailing list and Links (this document)
+
+user-guide.txt	-	User Guide to CPUFreq
+
+
+Mailing List
+------------
+There is a CPU frequency changing CVS commit and general list where
+you can report bugs, problems or submit patches. To post a message,
+send an email to cpufreq@www.linux.org.uk, to subscribe go to
+http://www.linux.org.uk/mailman/listinfo/cpufreq. Previous post to the
+mailing list are available to subscribers at
+http://www.linux.org.uk/mailman/private/cpufreq/.
+
+
+Links
+-----
+the FTP archives:
+* ftp://ftp.linux.org.uk/pub/linux/cpufreq/
+
+how to access the CVS repository:
+* http://cvs.arm.linux.org.uk/
+
+the CPUFreq Mailing list:
+* http://www.linux.org.uk/mailman/listinfo/cpufreq
+
+Clock and voltage scaling for the SA-1100:
+* http://www.lart.tudelft.nl/projects/scaling

Documentation/cpu-freq/user-guide.txt

+     CPU frequency and voltage scaling code in the Linux(TM) kernel
+
+
+		         L i n u x    C P U F r e q
+
+			     U S E R   G U I D E
+
+
+		    Dominik Brodowski  <linux@brodo.de>
+
+
+
+   Clock scaling allows you to change the clock speed of the CPUs on the
+    fly. This is a nice method to save battery power, because the lower
+            the clock speed, the less power the CPU consumes.
+
+
+Contents:
+---------
+1. Supported Architectures and Processors
+1.1 ARM
+1.2 x86
+1.3 sparc64
+
+2. "Policy" / "Governor"?
+2.1 Policy
+2.2 Governor
+
+3. How to change the CPU cpufreq policy and/or speed
+3.1 Preferred interface: sysfs
+3.2 Deprecated interfaces
+
+
+
+1. Supported Architectures and Processors
+=========================================
+
+1.1 ARM
+-------
+
+The following ARM processors are supported by cpufreq:
+
+ARM Integrator
+ARM-SA1100
+ARM-SA1110
+
+
+1.2 x86
+-------
+
+The following processors for the x86 architecture are supported by cpufreq:
+
+AMD Elan - SC400, SC410
+AMD mobile K6-2+
+AMD mobile K6-3+
+Cyrix Media GXm
+Intel mobile PIII [*] and Intel mobile PIII-M on certain chipsets
+Intel Pentium 4, Intel Xeon
+National Semiconductors Geode GX
+Transmeta Crusoe
+varios processors on some ACPI 2.0-compatible systems [**]
+
+[*] only certain Intel mobile PIII processors are supported. If you
+know that you own a speedstep-capable processor, pass the option
+"speedstep_coppermine=1" to the module speedstep.o
+
+[**] Only if "ACPI Processor Performance States" are available
+to the ACPI<->BIOS interface.
+
+
+1.3 sparc64
+-----------
+
+The following processors for the sparc64 architecture are supported by
+cpufreq:
+
+UltraSPARC-III
+
+
+
+2. "Policy" / "Governor" ?
+==========================
+
+Some CPU frequency scaling-capable processor switch between varios
+frequencies and operating voltages "on the fly" without any kernel or
+user involvement. This guarantuees very fast switching to a frequency
+which is high enough to serve the user's needs, but low enough to save
+power.
+
+
+2.1 Policy
+----------
+
+On these systems, all you can do is select the lower and upper
+frequency limit as well as whether you want more aggressive
+power-saving or more instantly avaialble processing power.
+
+
+2.2 Governor
+------------
+
+On all other cpufreq implementations, these boundaries still need to
+be set. Then, a "governor" must be selected. Such a "governor" decides
+what speed the processor shall run within the boundaries. One such
+"governor" is the "userspace" governor. This one allows the user - or
+a yet-to-implement userspace program - to decide what specific speed
+the processor shall run at.
+
+
+3. How to change the CPU cpufreq policy and/or speed
+====================================================
+
+3.1 Preferred Interface: sysfs
+------------------------------
+
+The preferred interface is located in the sysfs filesystem. If you
+mounted it at /sys, the cpufreq interface is located in the 
+cpu-device directory (e.g. /sys/devices/sys/cpu0/ for the first
+CPU).
+
+cpuinfo_min_freq :		this file shows the minimum operating
+				frequency the processor can run at(in kHz) 
+cpuinfo_max_freq :		this file shows the maximum operating
+				frequency the processor can run at(in kHz) 
+scaling_driver :		this file shows what cpufreq driver is
+				used to set the frequency on this CPU
+
+available_scaling_governors :	this file shows the CPUfreq governors
+				available in this kernel. You can see the
+				currently activated governor in
+
+scaling_governor,		and by "echoing" the name of another
+				governor you can change it. Please note
+				that some governors won't load - they only
+				work on some specific architectures or
+				processors.
+scaling_min_freq and 
+scaling_max_freq		show the current "policy limits" (in
+				kHz). By echoing new values into these
+				files, you can change these limits.
+
+
+If you have selected the "userspace" governor which allows you to
+set the CPU operating frequency to a specific value, you can read out
+the current frequency in
+
+scaling_setspeed.		By "echoing" a new frequency into this
+				you can change the speed of the CPU,
+				but only within the limits of
+				scaling_min_freq and scaling_max_freq.
+				
+
+3.2 Deprecated Interfaces
+-------------------------
+
+Depending on your kernel configuration, you might find the following 
+cpufreq-related files:
+/proc/cpufreq
+/proc/sys/cpu/*/speed
+/proc/sys/cpu/*/speed-min
+/proc/sys/cpu/*/speed-max
+
+These are files for deprecated interfaces to cpufreq, which offer far
+less functionality. Because of this, these interfaces aren't described
+here.
+