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Date: Fri, 28 Aug 2009 11:44:34 +0530
From: Arun R Bharadwaj <arun@linux.vnet.ibm.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH 2/4]: CPUIDLE: Introduce architecture independent
	cpuidle_pm_idle in drivers/cpuidle/cpuidle.c
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Cc: Gautham R Shenoy <ego@in.ibm.com>, "Pallipadi,
	Venkatesh" <venkatesh.pallipadi@intel.com>,
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* Peter Zijlstra <a.p.zijlstra@chello.nl> [2009-08-27 14:53:27]:

Hi Peter, Ben,

I've put the whole thing in a sort of a block diagram. Hope it
explains things more clearly.






				----------------
				|    CPUIDLE   |  (Select idle states like
				|   GOVERNORS  |   C1, C1e, C6 etc in case
				| (Menu/Ladder)|   x86 & nap, snooze in
				|	       |   case of POWER - based on
				----------------   latency & power req)
					^
					|
					|
					|
					|
					|
  ----------			-----------------	         -------------
  |	   |			|		|	         |  PSERIES  |
  |  ACPI  |------------------>	|    CPUIDLE	| <--------------|   IDLE    |
  |	   |			|		|	         |           |
  ----------			-----------------	         -------------

Main idle routine- pm_idle()			         Main idle routine-
							     ppc_md.power_save()

pm_idle = cpuidle_pm_idle;			         ppc_md.power_save =
(start using cpuidle's idle				      cpuidle_pm_idle();
 loop, which internally calls
 governor to select the right
 state to go into).


Relavent code snippet from drivers/cpuidle/cpuidle.c
-------------------------------------

static void cpuidle_idle_call(void)
{
	............
	............

	/* Call the menu_select() to select the idle state to enter. */
	next_state = cpuidle_curr_governor->select(dev);

	............
	............

	/*
	 * Enter the idle state previously selected. target_state->enter
	 * would call pseries_cpuidle_loop() which selects nap/snooze
	 * /
	dev->last_residency = target_state->enter(dev, target_state);
}

void cpuidle_install_idle_handler(void)
{
	.........
	.........
	cpuidle_pm_idle = cpuidle_idle_call;
}

--arun