[RFC,v3] cpuidle : Add support for pseudo-cpuidle driver

diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index c0aeedd66f02..1a0f227d61d6 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig
@@ -71,6 +71,15 @@  config HALTPOLL_CPUIDLE
 	 before halting in the guest (more efficient than polling in the
 	 host via halt_poll_ns for some scenarios).
 
+config TEST_CPUIDLE
+	tristate "cpuidle test driver"
+	default n
+	help
+	  This option enables a testing cpuidle driver, which allows the user
+	  to define custom idle states with their respective latencies & residencies.
+	  This is useful for testing the behaviour of governors on different
+	  sets of idle states.
+
 endif
 
 config ARCH_NEEDS_CPU_IDLE_COUPLED
diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
index f07800cbb43f..68ea7dc257b5 100644
--- a/drivers/cpuidle/Makefile
+++ b/drivers/cpuidle/Makefile
@@ -8,6 +8,7 @@  obj-$(CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED) += coupled.o
 obj-$(CONFIG_DT_IDLE_STATES)		  += dt_idle_states.o
 obj-$(CONFIG_ARCH_HAS_CPU_RELAX)	  += poll_state.o
 obj-$(CONFIG_HALTPOLL_CPUIDLE)		  += cpuidle-haltpoll.o
+obj-$(CONFIG_TEST_CPUIDLE)		  += cpuidle-test.o
 
 ##################################################################################
 # ARM SoC drivers
diff --git a/drivers/cpuidle/cpuidle-test.c b/drivers/cpuidle/cpuidle-test.c
new file mode 100644
index 000000000000..17ffce11cafc
--- /dev/null
+++ b/drivers/cpuidle/cpuidle-test.c
@@ -0,0 +1,289 @@ 
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  cpuidle-test - Test driver for cpuidle.
+ *
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/moduleparam.h>
+#include <linux/cpuidle.h>
+#include <linux/cpu.h>
+#include <linux/module.h>
+#include <linux/sched/idle.h>
+#include <linux/sched/clock.h>
+#include <linux/sched/idle.h>
+
+#define CPUIDLE_STATE_MAX	10
+#define MAX_PARAM_LENGTH	100
+
+static unsigned int nr_states = 4;
+static unsigned int sim_type = 1;
+static char name[MAX_PARAM_LENGTH];
+static char latency_us[MAX_PARAM_LENGTH];
+static char residency_us[MAX_PARAM_LENGTH];
+
+
+module_param(nr_states, uint, 0644);
+module_param(sim_type, uint, 0644);
+module_param_string(name, name, MAX_PARAM_LENGTH, 0644);
+module_param_string(latency_us, latency_us, MAX_PARAM_LENGTH, 0644);
+module_param_string(residency_us, residency_us, MAX_PARAM_LENGTH, 0644);
+
+static struct cpuidle_driver test_cpuidle_driver = {
+	.name		= "test_cpuidle",
+	.owner		= THIS_MODULE,
+};
+
+static struct cpuidle_state *cpuidle_state_table __read_mostly;
+
+static struct cpuidle_device __percpu *test_cpuidle_devices;
+static enum cpuhp_state test_hp_idlestate;
+
+
+static int __cpuidle idle_loop(struct cpuidle_device *dev,
+				struct cpuidle_driver *drv,
+				int index)
+{
+	u64 time_start;
+
+	local_irq_enable();
+
+	time_start = local_clock();
+	/*
+	 * Simulating entry latency into idle state.
+	 */
+	while (local_clock() - time_start < drv->states[index].exit_latency) {
+	}
+
+	if (!current_set_polling_and_test()) {
+		while (!need_resched())
+			cpu_relax();
+	}
+
+	time_start = local_clock();
+	/*
+	 * Simulating exit latency from idle state.
+	 */
+	while (local_clock() - time_start < drv->states[index].exit_latency) {
+	}
+
+	current_clr_polling();
+
+	return index;
+}
+
+	/*
+	 * Defining user specified custome set of idle states.
+	 */
+static struct cpuidle_state cpuidle_states[CPUIDLE_STATE_MAX] = {
+	{	.name = "snooze",
+		.exit_latency = 0,
+		.target_residency = 0,
+		.enter = idle_loop },
+};
+
+static struct cpuidle_state cpuidle_states_ppc[] = {
+	{	.name = "snooze",
+		.exit_latency = 0,
+		.target_residency = 0,
+		.enter = idle_loop },
+	{
+		.name = "stop0",
+		.exit_latency = 2,
+		.target_residency = 20,
+		.enter = idle_loop },
+	{
+		.name = "stop1",
+		.exit_latency = 5,
+		.target_residency = 50,
+		.enter = idle_loop },
+	{
+		.name = "stop2",
+		.exit_latency = 10,
+		.target_residency = 100,
+		.enter = idle_loop },
+};
+
+static struct cpuidle_state cpuidle_states_intel[] = {
+	{	.name = "poll",
+		.exit_latency = 0,
+		.target_residency = 0,
+		.enter = idle_loop },
+	{
+		.name = "c1",
+		.exit_latency = 2,
+		.target_residency = 2,
+		.enter = idle_loop },
+	{
+		.name = "c1e",
+		.exit_latency = 10,
+		.target_residency = 20,
+		.enter = idle_loop },
+	{
+		.name = "c3",
+		.exit_latency = 80,
+		.target_residency = 211,
+		.enter = idle_loop },
+};
+
+static int cpuidle_cpu_online(unsigned int cpu)
+{
+	struct cpuidle_device *dev;
+
+	dev = per_cpu_ptr(test_cpuidle_devices, cpu);
+	if (!dev->registered) {
+		dev->cpu = cpu;
+		if (cpuidle_register_device(dev)) {
+			pr_notice("cpuidle_register_device %d failed!\n", cpu);
+			return -EIO;
+		}
+	}
+
+	return 0;
+}
+
+static int cpuidle_cpu_dead(unsigned int cpu)
+{
+	struct cpuidle_device *dev;
+
+	dev = per_cpu_ptr(test_cpuidle_devices, cpu);
+	if (dev->registered)
+		cpuidle_unregister_device(dev);
+
+	return 0;
+}
+
+static int cpuidle_driver_init(void)
+{
+	int idle_state;
+	struct cpuidle_driver *drv = &test_cpuidle_driver;
+
+	drv->state_count = 0;
+
+	for (idle_state = 0; idle_state < nr_states; ++idle_state) {
+		/* Is the state not enabled? */
+		if (cpuidle_state_table[idle_state].enter == NULL)
+			continue;
+
+		drv->states[drv->state_count] =	/* structure copy */
+			cpuidle_state_table[idle_state];
+
+		drv->state_count += 1;
+	}
+
+	return 0;
+}
+
+static int add_cpuidle_states(void)
+{
+	/* Parse the module param and initialize the idle states here
+	 * in cpuidle_state_table.
+	 */
+	char *this_param;
+	char *input_name = name;
+	char *input_res = residency_us;
+	char *input_lat = latency_us;
+	int index = 1;
+	long temp;
+	int rc;
+
+	switch (sim_type) {
+	case 1:
+		cpuidle_state_table = cpuidle_states_ppc;
+		return 0;
+	case 2:
+		cpuidle_state_table = cpuidle_states_intel;
+		return 0;
+	case 3:
+		break;
+	default:
+		pr_warn("Sim value out of bound\n");
+		break;
+	}
+
+	if (strnlen(input_name, MAX_PARAM_LENGTH)) {
+		while ((this_param = strsep(&input_name, ",")) && index <= nr_states) {
+			strcpy(cpuidle_states[index].name, this_param);
+			cpuidle_states[index].enter = idle_loop;
+			index++;
+		}
+	}
+
+	if (strnlen(input_res, MAX_PARAM_LENGTH)) {
+		index = 1;
+		while ((this_param = strsep(&input_res, ",")) && index <= nr_states) {
+			rc = kstrtol(this_param, 10, &temp);
+			cpuidle_states[index].target_residency = temp;
+			index++;
+		}
+	}
+
+	if (strnlen(input_lat, MAX_PARAM_LENGTH)) {
+		index = 1;
+		while ((this_param = strsep(&input_lat, ",")) && index <= nr_states) {
+			rc = kstrtol(this_param, 10, &temp);
+			cpuidle_states[index].exit_latency = temp;
+			index++;
+		}
+	}
+
+	cpuidle_state_table = cpuidle_states;
+	return nr_states;
+}
+
+static void test_cpuidle_uninit(void)
+{
+	if (test_hp_idlestate)
+		cpuhp_remove_state(test_hp_idlestate);
+	cpuidle_unregister_driver(&test_cpuidle_driver);
+
+	free_percpu(test_cpuidle_devices);
+	test_cpuidle_devices = NULL;
+}
+
+static int __init test_cpuidle_init(void)
+{
+	int retval;
+
+	add_cpuidle_states();
+	cpuidle_driver_init();
+	retval = cpuidle_register(&test_cpuidle_driver, NULL);
+	if (retval) {
+		printk(KERN_DEBUG "Registration of test driver failed.\n");
+		return retval;
+	}
+
+	test_cpuidle_devices = alloc_percpu(struct cpuidle_device);
+	if (test_cpuidle_devices == NULL) {
+		cpuidle_unregister_driver(&test_cpuidle_driver);
+		return -ENOMEM;
+	}
+
+	retval = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					   "cpuidle/powernv:online",
+					   cpuidle_cpu_online,
+					   cpuidle_cpu_dead);
+
+	if (retval < 0) {
+		test_cpuidle_uninit();
+	} else {
+		test_hp_idlestate = retval;
+		retval = 0;
+	}
+
+	return retval;
+}
+
+static void __exit test_cpuidle_exit(void)
+{
+	test_cpuidle_uninit();
+}
+
+module_init(test_cpuidle_init);
+module_exit(test_cpuidle_exit);
+MODULE_DESCRIPTION("Test Cpuidle Driver");
+MODULE_AUTHOR("Abhishek Goel");
+MODULE_LICENSE("GPL");
+