[v10 PATCH 1/9]: cpuidle: Design documentation patch

[Arun R Bharadwaj <arun@linux.vnet.ibm.com>]

* Arun R Bharadwaj <arun@linux.vnet.ibm.com> [2009-12-02 15:24:27]:

This patch adds a little information about the redesigned cpuidle
infrastructure in Documentation/cpuidle/core.txt

Signed-off-by: Arun R Bharadwaj <arun@linux.vnet.ibm.com>
---
 Documentation/cpuidle/core.txt |   35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

Index: linux.trees.git/Documentation/cpuidle/core.txt
===================================================================
--- linux.trees.git.orig/Documentation/cpuidle/core.txt
+++ linux.trees.git/Documentation/cpuidle/core.txt
@@ -21,3 +21,38 @@ which can be used to switch governors at
 is meant for developer testing only. In normal usage, kernel picks the
 best governor based on governor ratings.
 SEE ALSO: sysfs.txt in this directory.
+
+Design:
+
+Cpuidle allows for registration of multiple sets of idle routines.
+The latest registered set is used by cpuidle governors as the current
+active set to choose the right idle state. This set is managed as a
+list and each time the newly registered set is added to the head of the
+list and made the current active set.
+
+An example of how this would work on x86 is shown below.
+
+-----------------					-----------------
+|		|					|		|
+| choose b/w	|	mwait is chosen			|    mwait	|
+| mwait, poll,	|-------------------------------------> |(current active|
+| default, c1e	|	register to cpuidle		|    set)	|
+|		|	with mwait as the idle routine	|		|
+-----------------					-----------------
+
+
+-----------------					-----------------
+|		|					|  c1, c2, c3	|
+|     ACPI	|	register to cpuidle		|   (current)	|
+|   discovery	|-------------------------------------> |---------------|
+|		|	with c1, c2, c3			|     mwait	|
+|		|	as set of idle routines		|		|
+-----------------					-----------------
+
+With this mechanism, a module can register and unregister its set of
+idle routines at run time in a clean manner.
+
+The main idle routine called inside cpu_idle() of every arch is defined in
+driver/cpuidle/cpuidle.c which would in turn call the idle routine selected
+by the governor. If the CONFIG_CPU_IDLE is disabled, the arch needs to
+provide an alternate definition for cpuidle_idle_call().