// SPDX-License-Identifier: GPL-2.0-only

  /*
   * acpi_pad.c ACPI Processor Aggregator Driver
   *
   * Copyright (c) 2009, Intel Corporation.

   */
  
  #include <linux/kernel.h>
  #include <linux/cpumask.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/types.h>
  #include <linux/kthread.h>

  #include <uapi/linux/sched/types.h>

  #include <linux/freezer.h>
  #include <linux/cpu.h>

  #include <linux/tick.h>

  #include <linux/slab.h>

  #include <linux/acpi.h>

  #include <asm/mwait.h>

  #include <xen/xen.h>

  #define ACPI_PROCESSOR_AGGREGATOR_CLASS	"acpi_pad"

  #define ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME "Processor Aggregator"
  #define ACPI_PROCESSOR_AGGREGATOR_NOTIFY 0x80
  static DEFINE_MUTEX(isolated_cpus_lock);

  static DEFINE_MUTEX(round_robin_lock);

  static unsigned long power_saving_mwait_eax;

  
  static unsigned char tsc_detected_unstable;
  static unsigned char tsc_marked_unstable;

  static void power_saving_mwait_init(void)
  {
  	unsigned int eax, ebx, ecx, edx;
  	unsigned int highest_cstate = 0;
  	unsigned int highest_subcstate = 0;
  	int i;
  
  	if (!boot_cpu_has(X86_FEATURE_MWAIT))
  		return;
  	if (boot_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
  		return;
  
  	cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
  
  	if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
  	    !(ecx & CPUID5_ECX_INTERRUPT_BREAK))
  		return;
  
  	edx >>= MWAIT_SUBSTATE_SIZE;
  	for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) {
  		if (edx & MWAIT_SUBSTATE_MASK) {
  			highest_cstate = i;
  			highest_subcstate = edx & MWAIT_SUBSTATE_MASK;
  		}
  	}
  	power_saving_mwait_eax = (highest_cstate << MWAIT_SUBSTATE_SIZE) |
  		(highest_subcstate - 1);

  #if defined(CONFIG_X86)

  	switch (boot_cpu_data.x86_vendor) {

  	case X86_VENDOR_HYGON:

  	case X86_VENDOR_AMD:
  	case X86_VENDOR_INTEL:

  	case X86_VENDOR_ZHAOXIN:

  		/*
  		 * AMD Fam10h TSC will tick in all
  		 * C/P/S0/S1 states when this bit is set.
  		 */

  		if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC))
  			tsc_detected_unstable = 1;

  		break;

  	default:

  		/* TSC could halt in idle */

  		tsc_detected_unstable = 1;

  	}
  #endif
  }
  
  static unsigned long cpu_weight[NR_CPUS];
  static int tsk_in_cpu[NR_CPUS] = {[0 ... NR_CPUS-1] = -1};
  static DECLARE_BITMAP(pad_busy_cpus_bits, NR_CPUS);
  static void round_robin_cpu(unsigned int tsk_index)
  {
  	struct cpumask *pad_busy_cpus = to_cpumask(pad_busy_cpus_bits);
  	cpumask_var_t tmp;
  	int cpu;

  	unsigned long min_weight = -1;

  	unsigned long preferred_cpu;

  
  	if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
  		return;

  	mutex_lock(&round_robin_lock);

  	cpumask_clear(tmp);
  	for_each_cpu(cpu, pad_busy_cpus)

  		cpumask_or(tmp, tmp, topology_sibling_cpumask(cpu));

  	cpumask_andnot(tmp, cpu_online_mask, tmp);
  	/* avoid HT sibilings if possible */
  	if (cpumask_empty(tmp))
  		cpumask_andnot(tmp, cpu_online_mask, pad_busy_cpus);
  	if (cpumask_empty(tmp)) {

  		mutex_unlock(&round_robin_lock);

  		free_cpumask_var(tmp);

  		return;
  	}
  	for_each_cpu(cpu, tmp) {
  		if (cpu_weight[cpu] < min_weight) {
  			min_weight = cpu_weight[cpu];
  			preferred_cpu = cpu;
  		}
  	}
  
  	if (tsk_in_cpu[tsk_index] != -1)
  		cpumask_clear_cpu(tsk_in_cpu[tsk_index], pad_busy_cpus);
  	tsk_in_cpu[tsk_index] = preferred_cpu;
  	cpumask_set_cpu(preferred_cpu, pad_busy_cpus);
  	cpu_weight[preferred_cpu]++;

  	mutex_unlock(&round_robin_lock);

  
  	set_cpus_allowed_ptr(current, cpumask_of(preferred_cpu));

  
  	free_cpumask_var(tmp);

  }
  
  static void exit_round_robin(unsigned int tsk_index)
  {
  	struct cpumask *pad_busy_cpus = to_cpumask(pad_busy_cpus_bits);
  	cpumask_clear_cpu(tsk_in_cpu[tsk_index], pad_busy_cpus);
  	tsk_in_cpu[tsk_index] = -1;
  }
  
  static unsigned int idle_pct = 5; /* percentage */

  static unsigned int round_robin_time = 1; /* second */

  static int power_saving_thread(void *data)
  {

  	int do_sleep;
  	unsigned int tsk_index = (unsigned long)data;
  	u64 last_jiffies = 0;

  	sched_set_fifo_low(current);

  
  	while (!kthread_should_stop()) {

  		unsigned long expire_time;

  		/* round robin to cpus */

  		expire_time = last_jiffies + round_robin_time * HZ;
  		if (time_before(expire_time, jiffies)) {

  			last_jiffies = jiffies;
  			round_robin_cpu(tsk_index);
  		}
  
  		do_sleep = 0;

  		expire_time = jiffies + HZ * (100 - idle_pct) / 100;
  
  		while (!need_resched()) {

  			if (tsc_detected_unstable && !tsc_marked_unstable) {
  				/* TSC could halt in idle, so notify users */
  				mark_tsc_unstable("TSC halts in idle");
  				tsc_marked_unstable = 1;
  			}

  			local_irq_disable();

  			tick_broadcast_enable();

  			tick_broadcast_enter();

  			stop_critical_timings();

  			mwait_idle_with_hints(power_saving_mwait_eax, 1);

  
  			start_critical_timings();

  			tick_broadcast_exit();

  			local_irq_enable();

  			if (time_before(expire_time, jiffies)) {

  				do_sleep = 1;
  				break;
  			}
  		}

  		/*
  		 * current sched_rt has threshold for rt task running time.
  		 * When a rt task uses 95% CPU time, the rt thread will be
  		 * scheduled out for 5% CPU time to not starve other tasks. But
  		 * the mechanism only works when all CPUs have RT task running,
  		 * as if one CPU hasn't RT task, RT task from other CPUs will
  		 * borrow CPU time from this CPU and cause RT task use > 95%

  		 * CPU time. To make 'avoid starvation' work, takes a nap here.

  		 */

  		if (unlikely(do_sleep))

  			schedule_timeout_killable(HZ * idle_pct / 100);

  
  		/* If an external event has set the need_resched flag, then
  		 * we need to deal with it, or this loop will continue to
  		 * spin without calling __mwait().
  		 */
  		if (unlikely(need_resched()))
  			schedule();

  	}
  
  	exit_round_robin(tsk_index);
  	return 0;
  }
  
  static struct task_struct *ps_tsks[NR_CPUS];
  static unsigned int ps_tsk_num;
  static int create_power_saving_task(void)
  {

  	int rc;

  	ps_tsks[ps_tsk_num] = kthread_run(power_saving_thread,
  		(void *)(unsigned long)ps_tsk_num,

  		"acpi_pad/%d", ps_tsk_num);

  
  	if (IS_ERR(ps_tsks[ps_tsk_num])) {
  		rc = PTR_ERR(ps_tsks[ps_tsk_num]);

  		ps_tsks[ps_tsk_num] = NULL;

  	} else {
  		rc = 0;
  		ps_tsk_num++;
  	}

  
  	return rc;

  }
  
  static void destroy_power_saving_task(void)
  {
  	if (ps_tsk_num > 0) {
  		ps_tsk_num--;
  		kthread_stop(ps_tsks[ps_tsk_num]);

  		ps_tsks[ps_tsk_num] = NULL;

  	}
  }
  
  static void set_power_saving_task_num(unsigned int num)
  {
  	if (num > ps_tsk_num) {
  		while (ps_tsk_num < num) {
  			if (create_power_saving_task())
  				return;
  		}
  	} else if (num < ps_tsk_num) {
  		while (ps_tsk_num > num)
  			destroy_power_saving_task();
  	}
  }

  static void acpi_pad_idle_cpus(unsigned int num_cpus)

  {
  	get_online_cpus();
  
  	num_cpus = min_t(unsigned int, num_cpus, num_online_cpus());
  	set_power_saving_task_num(num_cpus);
  
  	put_online_cpus();

  }
  
  static uint32_t acpi_pad_idle_cpus_num(void)
  {
  	return ps_tsk_num;
  }
  
  static ssize_t acpi_pad_rrtime_store(struct device *dev,
  	struct device_attribute *attr, const char *buf, size_t count)
  {
  	unsigned long num;

  	if (kstrtoul(buf, 0, &num))

  		return -EINVAL;
  	if (num < 1 || num >= 100)
  		return -EINVAL;
  	mutex_lock(&isolated_cpus_lock);
  	round_robin_time = num;
  	mutex_unlock(&isolated_cpus_lock);
  	return count;
  }
  
  static ssize_t acpi_pad_rrtime_show(struct device *dev,
  	struct device_attribute *attr, char *buf)
  {

  	return scnprintf(buf, PAGE_SIZE, "%d
  ", round_robin_time);

  }
  static DEVICE_ATTR(rrtime, S_IRUGO|S_IWUSR,
  	acpi_pad_rrtime_show,
  	acpi_pad_rrtime_store);
  
  static ssize_t acpi_pad_idlepct_store(struct device *dev,
  	struct device_attribute *attr, const char *buf, size_t count)
  {
  	unsigned long num;

  	if (kstrtoul(buf, 0, &num))

  		return -EINVAL;
  	if (num < 1 || num >= 100)
  		return -EINVAL;
  	mutex_lock(&isolated_cpus_lock);
  	idle_pct = num;
  	mutex_unlock(&isolated_cpus_lock);
  	return count;
  }
  
  static ssize_t acpi_pad_idlepct_show(struct device *dev,
  	struct device_attribute *attr, char *buf)
  {

  	return scnprintf(buf, PAGE_SIZE, "%d
  ", idle_pct);

  }
  static DEVICE_ATTR(idlepct, S_IRUGO|S_IWUSR,
  	acpi_pad_idlepct_show,
  	acpi_pad_idlepct_store);
  
  static ssize_t acpi_pad_idlecpus_store(struct device *dev,
  	struct device_attribute *attr, const char *buf, size_t count)
  {
  	unsigned long num;

  	if (kstrtoul(buf, 0, &num))

  		return -EINVAL;
  	mutex_lock(&isolated_cpus_lock);
  	acpi_pad_idle_cpus(num);
  	mutex_unlock(&isolated_cpus_lock);
  	return count;
  }
  
  static ssize_t acpi_pad_idlecpus_show(struct device *dev,
  	struct device_attribute *attr, char *buf)
  {

  	return cpumap_print_to_pagebuf(false, buf,
  				       to_cpumask(pad_busy_cpus_bits));

  }

  static DEVICE_ATTR(idlecpus, S_IRUGO|S_IWUSR,
  	acpi_pad_idlecpus_show,
  	acpi_pad_idlecpus_store);
  
  static int acpi_pad_add_sysfs(struct acpi_device *device)
  {
  	int result;
  
  	result = device_create_file(&device->dev, &dev_attr_idlecpus);
  	if (result)
  		return -ENODEV;
  	result = device_create_file(&device->dev, &dev_attr_idlepct);
  	if (result) {
  		device_remove_file(&device->dev, &dev_attr_idlecpus);
  		return -ENODEV;
  	}
  	result = device_create_file(&device->dev, &dev_attr_rrtime);
  	if (result) {
  		device_remove_file(&device->dev, &dev_attr_idlecpus);
  		device_remove_file(&device->dev, &dev_attr_idlepct);
  		return -ENODEV;
  	}
  	return 0;
  }
  
  static void acpi_pad_remove_sysfs(struct acpi_device *device)
  {
  	device_remove_file(&device->dev, &dev_attr_idlecpus);
  	device_remove_file(&device->dev, &dev_attr_idlepct);
  	device_remove_file(&device->dev, &dev_attr_rrtime);
  }

  /*
   * Query firmware how many CPUs should be idle
   * return -1 on failure
   */
  static int acpi_pad_pur(acpi_handle handle)

  {
  	struct acpi_buffer buffer = {ACPI_ALLOCATE_BUFFER, NULL};

  	union acpi_object *package;

  	int num = -1;

  	if (ACPI_FAILURE(acpi_evaluate_object(handle, "_PUR", NULL, &buffer)))

  		return num;

  
  	if (!buffer.length || !buffer.pointer)

  		return num;

  	package = buffer.pointer;

  
  	if (package->type == ACPI_TYPE_PACKAGE &&
  		package->package.count == 2 &&
  		package->package.elements[0].integer.value == 1) /* rev 1 */
  
  		num = package->package.elements[1].integer.value;

  	kfree(buffer.pointer);

  	return num;

  }

  static void acpi_pad_handle_notify(acpi_handle handle)
  {

  	int num_cpus;

  	uint32_t idle_cpus;

  	struct acpi_buffer param = {
  		.length = 4,
  		.pointer = (void *)&idle_cpus,
  	};

  
  	mutex_lock(&isolated_cpus_lock);

  	num_cpus = acpi_pad_pur(handle);
  	if (num_cpus < 0) {

  		mutex_unlock(&isolated_cpus_lock);
  		return;
  	}

  	acpi_pad_idle_cpus(num_cpus);

  	idle_cpus = acpi_pad_idle_cpus_num();

  	acpi_evaluate_ost(handle, ACPI_PROCESSOR_AGGREGATOR_NOTIFY, 0, &param);

  	mutex_unlock(&isolated_cpus_lock);
  }
  
  static void acpi_pad_notify(acpi_handle handle, u32 event,
  	void *data)
  {
  	struct acpi_device *device = data;
  
  	switch (event) {
  	case ACPI_PROCESSOR_AGGREGATOR_NOTIFY:
  		acpi_pad_handle_notify(handle);

  		acpi_bus_generate_netlink_event(device->pnp.device_class,
  			dev_name(&device->dev), event, 0);
  		break;
  	default:

  		pr_warn("Unsupported event [0x%x]
  ", event);

  		break;
  	}
  }
  
  static int acpi_pad_add(struct acpi_device *device)
  {
  	acpi_status status;
  
  	strcpy(acpi_device_name(device), ACPI_PROCESSOR_AGGREGATOR_DEVICE_NAME);
  	strcpy(acpi_device_class(device), ACPI_PROCESSOR_AGGREGATOR_CLASS);
  
  	if (acpi_pad_add_sysfs(device))
  		return -ENODEV;
  
  	status = acpi_install_notify_handler(device->handle,
  		ACPI_DEVICE_NOTIFY, acpi_pad_notify, device);
  	if (ACPI_FAILURE(status)) {
  		acpi_pad_remove_sysfs(device);
  		return -ENODEV;
  	}
  
  	return 0;
  }

  static int acpi_pad_remove(struct acpi_device *device)

  {
  	mutex_lock(&isolated_cpus_lock);
  	acpi_pad_idle_cpus(0);
  	mutex_unlock(&isolated_cpus_lock);
  
  	acpi_remove_notify_handler(device->handle,
  		ACPI_DEVICE_NOTIFY, acpi_pad_notify);
  	acpi_pad_remove_sysfs(device);
  	return 0;
  }
  
  static const struct acpi_device_id pad_device_ids[] = {
  	{"ACPI000C", 0},
  	{"", 0},
  };
  MODULE_DEVICE_TABLE(acpi, pad_device_ids);
  
  static struct acpi_driver acpi_pad_driver = {
  	.name = "processor_aggregator",
  	.class = ACPI_PROCESSOR_AGGREGATOR_CLASS,
  	.ids = pad_device_ids,
  	.ops = {
  		.add = acpi_pad_add,
  		.remove = acpi_pad_remove,
  	},
  };
  
  static int __init acpi_pad_init(void)
  {

  	/* Xen ACPI PAD is used when running as Xen Dom0. */
  	if (xen_initial_domain())
  		return -ENODEV;

  	power_saving_mwait_init();
  	if (power_saving_mwait_eax == 0)
  		return -EINVAL;
  
  	return acpi_bus_register_driver(&acpi_pad_driver);
  }
  
  static void __exit acpi_pad_exit(void)
  {
  	acpi_bus_unregister_driver(&acpi_pad_driver);
  }
  
  module_init(acpi_pad_init);
  module_exit(acpi_pad_exit);
  MODULE_AUTHOR("Shaohua Li<shaohua.li@intel.com>");
  MODULE_DESCRIPTION("ACPI Processor Aggregator Driver");
  MODULE_LICENSE("GPL");