xref: /linux/drivers/cpuidle/cpuidle-big_little.c (revision eba1c71819d210f5e0d522571f9b8abce94fe9c5)

/*
 * Copyright (c) 2013 ARM/Linaro
 *
 * Authors: Daniel Lezcano <daniel.lezcano@linaro.org>
 *          Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
 *          Nicolas Pitre <nicolas.pitre@linaro.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Maintainer: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
 * Maintainer: Daniel Lezcano <daniel.lezcano@linaro.org>
 */
#include <linux/cpuidle.h>
#include <linux/cpu_pm.h>
#include <linux/slab.h>
#include <linux/of.h>

#include <asm/cpu.h>
#include <asm/cputype.h>
#include <asm/cpuidle.h>
#include <asm/mcpm.h>
#include <asm/smp_plat.h>
#include <asm/suspend.h>

static int bl_enter_powerdown(struct cpuidle_device *dev,
			      struct cpuidle_driver *drv, int idx);

/*
 * NB: Owing to current menu governor behaviour big and LITTLE
 * index 1 states have to define exit_latency and target_residency for
 * cluster state since, when all CPUs in a cluster hit it, the cluster
 * can be shutdown. This means that when a single CPU enters this state
 * the exit_latency and target_residency values are somewhat overkill.
 * There is no notion of cluster states in the menu governor, so CPUs
 * have to define CPU states where possibly the cluster will be shutdown
 * depending on the state of other CPUs. idle states entry and exit happen
 * at random times; however the cluster state provides target_residency
 * values as if all CPUs in a cluster enter the state at once; this is
 * somewhat optimistic and behaviour should be fixed either in the governor
 * or in the MCPM back-ends.
 * To make this driver 100% generic the number of states and the exit_latency
 * target_residency values must be obtained from device tree bindings.
 *
 * exit_latency: refers to the TC2 vexpress test chip and depends on the
 * current cluster operating point. It is the time it takes to get the CPU
 * up and running when the CPU is powered up on cluster wake-up from shutdown.
 * Current values for big and LITTLE clusters are provided for clusters
 * running at default operating points.
 *
 * target_residency: it is the minimum amount of time the cluster has
 * to be down to break even in terms of power consumption. cluster
 * shutdown has inherent dynamic power costs (L2 writebacks to DRAM
 * being the main factor) that depend on the current operating points.
 * The current values for both clusters are provided for a CPU whose half
 * of L2 lines are dirty and require cleaning to DRAM, and takes into
 * account leakage static power values related to the vexpress TC2 testchip.
 */
static struct cpuidle_driver bl_idle_little_driver = {
	.name = "little_idle",
	.owner = THIS_MODULE,
	.states[0] = ARM_CPUIDLE_WFI_STATE,
	.states[1] = {
		.enter			= bl_enter_powerdown,
		.exit_latency		= 700,
		.target_residency	= 2500,
		.flags			= CPUIDLE_FLAG_TIME_VALID |
					  CPUIDLE_FLAG_TIMER_STOP,
		.name			= "C1",
		.desc			= "ARM little-cluster power down",
	},
	.state_count = 2,
};

static struct cpuidle_driver bl_idle_big_driver = {
	.name = "big_idle",
	.owner = THIS_MODULE,
	.states[0] = ARM_CPUIDLE_WFI_STATE,
	.states[1] = {
		.enter			= bl_enter_powerdown,
		.exit_latency		= 500,
		.target_residency	= 2000,
		.flags			= CPUIDLE_FLAG_TIME_VALID |
					  CPUIDLE_FLAG_TIMER_STOP,
		.name			= "C1",
		.desc			= "ARM big-cluster power down",
	},
	.state_count = 2,
};

/*
 * notrace prevents trace shims from getting inserted where they
 * should not. Global jumps and ldrex/strex must not be inserted
 * in power down sequences where caches and MMU may be turned off.
 */
static int notrace bl_powerdown_finisher(unsigned long arg)
{
	/* MCPM works with HW CPU identifiers */
	unsigned int mpidr = read_cpuid_mpidr();
	unsigned int cluster = MPIDR_AFFINITY_LEVEL(mpidr, 1);
	unsigned int cpu = MPIDR_AFFINITY_LEVEL(mpidr, 0);

	mcpm_set_entry_vector(cpu, cluster, cpu_resume);

	/*
	 * Residency value passed to mcpm_cpu_suspend back-end
	 * has to be given clear semantics. Set to 0 as a
	 * temporary value.
	 */
	mcpm_cpu_suspend(0);

	/* return value != 0 means failure */
	return 1;
}

/**
 * bl_enter_powerdown - Programs CPU to enter the specified state
 * @dev: cpuidle device
 * @drv: The target state to be programmed
 * @idx: state index
 *
 * Called from the CPUidle framework to program the device to the
 * specified target state selected by the governor.
 */
static int bl_enter_powerdown(struct cpuidle_device *dev,
				struct cpuidle_driver *drv, int idx)
{
	cpu_pm_enter();

	cpu_suspend(0, bl_powerdown_finisher);

	/* signals the MCPM core that CPU is out of low power state */
	mcpm_cpu_powered_up();

	cpu_pm_exit();

	return idx;
}

static int __init bl_idle_driver_init(struct cpuidle_driver *drv, int part_id)
{
	struct cpumask *cpumask;
	int cpu;

	cpumask = kzalloc(cpumask_size(), GFP_KERNEL);
	if (!cpumask)
		return -ENOMEM;

	for_each_possible_cpu(cpu)
		if (smp_cpuid_part(cpu) == part_id)
			cpumask_set_cpu(cpu, cpumask);

	drv->cpumask = cpumask;

	return 0;
}

static const struct of_device_id compatible_machine_match[] = {
	{ .compatible = "arm,vexpress,v2p-ca15_a7" },
	{ .compatible = "samsung,exynos5420" },
	{},
};

static int __init bl_idle_init(void)
{
	int ret;
	struct device_node *root = of_find_node_by_path("/");

	if (!root)
		return -ENODEV;

	/*
	 * Initialize the driver just for a compliant set of machines
	 */
	if (!of_match_node(compatible_machine_match, root))
		return -ENODEV;
	/*
	 * For now the differentiation between little and big cores
	 * is based on the part number. A7 cores are considered little
	 * cores, A15 are considered big cores. This distinction may
	 * evolve in the future with a more generic matching approach.
	 */
	ret = bl_idle_driver_init(&bl_idle_little_driver,
				  ARM_CPU_PART_CORTEX_A7);
	if (ret)
		return ret;

	ret = bl_idle_driver_init(&bl_idle_big_driver, ARM_CPU_PART_CORTEX_A15);
	if (ret)
		goto out_uninit_little;

	ret = cpuidle_register(&bl_idle_little_driver, NULL);
	if (ret)
		goto out_uninit_big;

	ret = cpuidle_register(&bl_idle_big_driver, NULL);
	if (ret)
		goto out_unregister_little;

	return 0;

out_unregister_little:
	cpuidle_unregister(&bl_idle_little_driver);
out_uninit_big:
	kfree(bl_idle_big_driver.cpumask);
out_uninit_little:
	kfree(bl_idle_little_driver.cpumask);

	return ret;
}
device_initcall(bl_idle_init);