linux/arch/ia64/kernel/smpboot.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * SMP boot-related support
 *
 * Copyright (C) 1998-2003, 2005 Hewlett-Packard Co
 *	David Mosberger-Tang <davidm@hpl.hp.com>
 * Copyright (C) 2001, 2004-2005 Intel Corp
 * 	Rohit Seth <rohit.seth@intel.com>
 * 	Suresh Siddha <suresh.b.siddha@intel.com>
 * 	Gordon Jin <gordon.jin@intel.com>
 *	Ashok Raj  <ashok.raj@intel.com>
 *
 * 01/05/16 Rohit Seth <rohit.seth@intel.com>	Moved SMP booting functions from smp.c to here.
 * 01/04/27 David Mosberger <davidm@hpl.hp.com>	Added ITC synching code.
 * 02/07/31 David Mosberger <davidm@hpl.hp.com>	Switch over to hotplug-CPU boot-sequence.
 *						smp_boot_cpus()/smp_commence() is replaced by
 *						smp_prepare_cpus()/__cpu_up()/smp_cpus_done().
 * 04/06/21 Ashok Raj		<ashok.raj@intel.com> Added CPU Hotplug Support
 * 04/12/26 Jin Gordon <gordon.jin@intel.com>
 * 04/12/26 Rohit Seth <rohit.seth@intel.com>
 *						Add multi-threading and multi-core detection
 * 05/01/30 Suresh Siddha <suresh.b.siddha@intel.com>
 *						Setup cpu_sibling_map and cpu_core_map
 */

#include <linux/module.h>
#include <linux/acpi.h>
#include <linux/memblock.h>
#include <linux/cpu.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/irq.h>
#include <linux/kernel.h>
#include <linux/kernel_stat.h>
#include <linux/mm.h>
#include <linux/notifier.h>
#include <linux/smp.h>
#include <linux/spinlock.h>
#include <linux/efi.h>
#include <linux/percpu.h>
#include <linux/bitops.h>

#include <linux/atomic.h>
#include <asm/cache.h>
#include <asm/current.h>
#include <asm/delay.h>
#include <asm/efi.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/mca.h>
#include <asm/page.h>
#include <asm/processor.h>
#include <asm/ptrace.h>
#include <asm/sal.h>
#include <asm/tlbflush.h>
#include <asm/unistd.h>

#define SMP_DEBUG 0

#if SMP_DEBUG
#define Dprintk(x...)  printk(x)
#else
#define Dprintk(x...)
#endif

#ifdef CONFIG_HOTPLUG_CPU
#ifdef CONFIG_PERMIT_BSP_REMOVE
#define bsp_remove_ok	1
#else
#define bsp_remove_ok	0
#endif

/*
 * Global array allocated for NR_CPUS at boot time
 */
struct sal_to_os_boot sal_boot_rendez_state[NR_CPUS];

/*
 * start_ap in head.S uses this to store current booting cpu
 * info.
 */
struct sal_to_os_boot *sal_state_for_booting_cpu = &sal_boot_rendez_state[0];

#define set_brendez_area(x) (sal_state_for_booting_cpu = &sal_boot_rendez_state[(x)]);

#else
#define set_brendez_area(x)
#endif


/*
 * ITC synchronization related stuff:
 */
#define MASTER	(0)
#define SLAVE	(SMP_CACHE_BYTES/8)

#define NUM_ROUNDS	64	/* magic value */
#define NUM_ITERS	5	/* likewise */

static DEFINE_SPINLOCK(itc_sync_lock);
static volatile unsigned long go[SLAVE + 1];

#define DEBUG_ITC_SYNC	0

extern void start_ap (void);
extern unsigned long ia64_iobase;

struct task_struct *task_for_booting_cpu;

/*
 * State for each CPU
 */
DEFINE_PER_CPU(int, cpu_state);

cpumask_t cpu_core_map[NR_CPUS] __cacheline_aligned;
EXPORT_SYMBOL(cpu_core_map);
DEFINE_PER_CPU_SHARED_ALIGNED(cpumask_t, cpu_sibling_map);
EXPORT_PER_CPU_SYMBOL(cpu_sibling_map);

int smp_num_siblings = 1;

/* which logical CPU number maps to which CPU (physical APIC ID) */
volatile int ia64_cpu_to_sapicid[NR_CPUS];
EXPORT_SYMBOL(ia64_cpu_to_sapicid);

static cpumask_t cpu_callin_map;

struct smp_boot_data smp_boot_data __initdata;

unsigned long ap_wakeup_vector = -1; /* External Int use to wakeup APs */

char __initdata no_int_routing;

unsigned char smp_int_redirect; /* are INT and IPI redirectable by the chipset? */

#ifdef CONFIG_FORCE_CPEI_RETARGET
#define CPEI_OVERRIDE_DEFAULT	(1)
#else
#define CPEI_OVERRIDE_DEFAULT	(0)
#endif

unsigned int force_cpei_retarget = CPEI_OVERRIDE_DEFAULT;

static int __init
cmdl_force_cpei(char *str)
{
	int value=0;

	get_option (&str, &value);
	force_cpei_retarget = value;

	return 1;
}

__setup("force_cpei=", cmdl_force_cpei);

static int __init
nointroute (char *str)
{
	no_int_routing = 1;
	printk ("no_int_routing on\n");
	return 1;
}

__setup("nointroute", nointroute);

static void fix_b0_for_bsp(void)
{
#ifdef CONFIG_HOTPLUG_CPU
	int cpuid;
	static int fix_bsp_b0 = 1;

	cpuid = smp_processor_id();

	/*
	 * Cache the b0 value on the first AP that comes up
	 */
	if (!(fix_bsp_b0 && cpuid))
		return;

	sal_boot_rendez_state[0].br[0] = sal_boot_rendez_state[cpuid].br[0];
	printk ("Fixed BSP b0 value from CPU %d\n", cpuid);

	fix_bsp_b0 = 0;
#endif
}

void
sync_master (void *arg)
{
	unsigned long flags, i;

	go[MASTER] = 0;

	local_irq_save(flags);
	{
		for (i = 0; i < NUM_ROUNDS*NUM_ITERS; ++i) {
			while (!go[MASTER])
				cpu_relax();
			go[MASTER] = 0;
			go[SLAVE] = ia64_get_itc();
		}
	}
	local_irq_restore(flags);
}

/*
 * Return the number of cycles by which our itc differs from the itc on the master
 * (time-keeper) CPU.  A positive number indicates our itc is ahead of the master,
 * negative that it is behind.
 */
static inline long
get_delta (long *rt, long *master)
{
	unsigned long best_t0 = 0, best_t1 = ~0UL, best_tm = 0;
	unsigned long tcenter, t0, t1, tm;
	long i;

	for (i = 0; i < NUM_ITERS; ++i) {
		t0 = ia64_get_itc();
		go[MASTER] = 1;
		while (!(tm = go[SLAVE]))
			cpu_relax();
		go[SLAVE] = 0;
		t1 = ia64_get_itc();

		if (t1 - t0 < best_t1 - best_t0)
			best_t0 = t0, best_t1 = t1, best_tm = tm;
	}

	*rt = best_t1 - best_t0;
	*master = best_tm - best_t0;

	/* average best_t0 and best_t1 without overflow: */
	tcenter = (best_t0/2 + best_t1/2);
	if (best_t0 % 2 + best_t1 % 2 == 2)
		++tcenter;
	return tcenter - best_tm;
}

/*
 * Synchronize ar.itc of the current (slave) CPU with the ar.itc of the MASTER CPU
 * (normally the time-keeper CPU).  We use a closed loop to eliminate the possibility of
 * unaccounted-for errors (such as getting a machine check in the middle of a calibration
 * step).  The basic idea is for the slave to ask the master what itc value it has and to
 * read its own itc before and after the master responds.  Each iteration gives us three
 * timestamps:
 *
 *	slave		master
 *
 *	t0 ---\
 *             ---\
 *		   --->
 *			tm
 *		   /---
 *	       /---
 *	t1 <---
 *
 *
 * The goal is to adjust the slave's ar.itc such that tm falls exactly half-way between t0
 * and t1.  If we achieve this, the clocks are synchronized provided the interconnect
 * between the slave and the master is symmetric.  Even if the interconnect were
 * asymmetric, we would still know that the synchronization error is smaller than the
 * roundtrip latency (t0 - t1).
 *
 * When the interconnect is quiet and symmetric, this lets us synchronize the itc to
 * within one or two cycles.  However, we can only *guarantee* that the synchronization is
 * accurate to within a round-trip time, which is typically in the range of several
 * hundred cycles (e.g., ~500 cycles).  In practice, this means that the itc's are usually
 * almost perfectly synchronized, but we shouldn't assume that the accuracy is much better
 * than half a micro second or so.
 */
void
ia64_sync_itc (unsigned int master)
{
	long i, delta, adj, adjust_latency = 0, done = 0;
	unsigned long flags, rt, master_time_stamp, bound;
#if DEBUG_ITC_SYNC
	struct {
		long rt;	/* roundtrip time */
		long master;	/* master's timestamp */
		long diff;	/* difference between midpoint and master's timestamp */
		long lat;	/* estimate of itc adjustment latency */
	} t[NUM_ROUNDS];
#endif

	/*
	 * Make sure local timer ticks are disabled while we sync.  If
	 * they were enabled, we'd have to worry about nasty issues
	 * like setting the ITC ahead of (or a long time before) the
	 * next scheduled tick.
	 */
	BUG_ON((ia64_get_itv() & (1 << 16)) == 0);

	go[MASTER] = 1;

	if (smp_call_function_single(master, sync_master, NULL, 0) < 0) {
		printk(KERN_ERR "sync_itc: failed to get attention of CPU %u!\n", master);
		return;
	}

	while (go[MASTER])
		cpu_relax();	/* wait for master to be ready */

	spin_lock_irqsave(&itc_sync_lock, flags);
	{
		for (i = 0; i < NUM_ROUNDS; ++i) {
			delta = get_delta(&rt, &master_time_stamp);
			if (delta == 0) {
				done = 1;	/* let's lock on to this... */
				bound = rt;
			}

			if (!done) {
				if (i > 0) {
					adjust_latency += -delta;
					adj = -delta + adjust_latency/4;
				} else
					adj = -delta;

				ia64_set_itc(ia64_get_itc() + adj);
			}
#if DEBUG_ITC_SYNC
			t[i].rt = rt;
			t[i].master = master_time_stamp;
			t[i].diff = delta;
			t[i].lat = adjust_latency/4;
#endif
		}
	}
	spin_unlock_irqrestore(&itc_sync_lock, flags);

#if DEBUG_ITC_SYNC
	for (i = 0; i < NUM_ROUNDS; ++i)
		printk("rt=%5ld master=%5ld diff=%5ld adjlat=%5ld\n",
		       t[i].rt, t[i].master, t[i].diff, t[i].lat);
#endif

	printk(KERN_INFO "CPU %d: synchronized ITC with CPU %u (last diff %ld cycles, "
	       "maxerr %lu cycles)\n", smp_processor_id(), master, delta, rt);
}

/*
 * Ideally sets up per-cpu profiling hooks.  Doesn't do much now...
 */
static inline void smp_setup_percpu_timer(void)
{
}

static void
smp_callin (void)
{
	int cpuid, phys_id, itc_master;
	struct cpuinfo_ia64 *last_cpuinfo, *this_cpuinfo;
	extern void ia64_init_itm(void);
	extern volatile int time_keeper_id;

	cpuid = smp_processor_id();
	phys_id = hard_smp_processor_id();
	itc_master = time_keeper_id;

	if (cpu_online(cpuid)) {
		printk(KERN_ERR "huh, phys CPU#0x%x, CPU#0x%x already present??\n",
		       phys_id, cpuid);
		BUG();
	}

	fix_b0_for_bsp();

	/*
	 * numa_node_id() works after this.
	 */
	set_numa_node(cpu_to_node_map[cpuid]);
	set_numa_mem(local_memory_node(cpu_to_node_map[cpuid]));

	spin_lock(&vector_lock);
	/* Setup the per cpu irq handling data structures */
	__setup_vector_irq(cpuid);
	notify_cpu_starting(cpuid);
	set_cpu_online(cpuid, true);
	per_cpu(cpu_state, cpuid) = CPU_ONLINE;
	spin_unlock(&vector_lock);

	smp_setup_percpu_timer();

	ia64_mca_cmc_vector_setup();	/* Setup vector on AP */

	local_irq_enable();

	if (!(sal_platform_features & IA64_SAL_PLATFORM_FEATURE_ITC_DRIFT)) {
		/*
		 * Synchronize the ITC with the BP.  Need to do this after irqs are
		 * enabled because ia64_sync_itc() calls smp_call_function_single(), which
		 * calls spin_unlock_bh(), which calls spin_unlock_bh(), which calls
		 * local_bh_enable(), which bugs out if irqs are not enabled...
		 */
		Dprintk("Going to syncup ITC with ITC Master.\n");
		ia64_sync_itc(itc_master);
	}

	/*
	 * Get our bogomips.
	 */
	ia64_init_itm();

	/*
	 * Delay calibration can be skipped if new processor is identical to the
	 * previous processor.
	 */
	last_cpuinfo = cpu_data(cpuid - 1);
	this_cpuinfo = local_cpu_data;
	if (last_cpuinfo->itc_freq != this_cpuinfo->itc_freq ||
	    last_cpuinfo->proc_freq != this_cpuinfo->proc_freq ||
	    last_cpuinfo->features != this_cpuinfo->features ||
	    last_cpuinfo->revision != this_cpuinfo->revision ||
	    last_cpuinfo->family != this_cpuinfo->family ||
	    last_cpuinfo->archrev != this_cpuinfo->archrev ||
	    last_cpuinfo->model != this_cpuinfo->model)
		calibrate_delay();
	local_cpu_data->loops_per_jiffy = loops_per_jiffy;

	/*
	 * Allow the master to continue.
	 */
	cpumask_set_cpu(cpuid, &cpu_callin_map);
	Dprintk("Stack on CPU %d at about %p\n",cpuid, &cpuid);
}


/*
 * Activate a secondary processor.  head.S calls this.
 */
int
start_secondary (void *unused)
{
	/* Early console may use I/O ports */
	ia64_set_kr(IA64_KR_IO_BASE, __pa(ia64_iobase));
#ifndef CONFIG_PRINTK_TIME
	Dprintk("start_secondary: starting CPU 0x%x\n", hard_smp_processor_id());
#endif
	efi_map_pal_code();
	cpu_init();
	smp_callin();

	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
	return 0;
}

static int
do_boot_cpu (int sapicid, int cpu, struct task_struct *idle)
{
	int timeout;

	task_for_booting_cpu = idle;
	Dprintk("Sending wakeup vector %lu to AP 0x%x/0x%x.\n", ap_wakeup_vector, cpu, sapicid);

	set_brendez_area(cpu);
	ia64_send_ipi(cpu, ap_wakeup_vector, IA64_IPI_DM_INT, 0);

	/*
	 * Wait 10s total for the AP to start
	 */
	Dprintk("Waiting on callin_map ...");
	for (timeout = 0; timeout < 100000; timeout++) {
		if (cpumask_test_cpu(cpu, &cpu_callin_map))
			break;  /* It has booted */
		barrier(); /* Make sure we re-read cpu_callin_map */
		udelay(100);
	}
	Dprintk("\n");

	if (!cpumask_test_cpu(cpu, &cpu_callin_map)) {
		printk(KERN_ERR "Processor 0x%x/0x%x is stuck.\n", cpu, sapicid);
		ia64_cpu_to_sapicid[cpu] = -1;
		set_cpu_online(cpu, false);  /* was set in smp_callin() */
		return -EINVAL;
	}
	return 0;
}

static int __init
decay (char *str)
{
	int ticks;
	get_option (&str, &ticks);
	return 1;
}

__setup("decay=", decay);

/*
 * Initialize the logical CPU number to SAPICID mapping
 */
void __init
smp_build_cpu_map (void)
{
	int sapicid, cpu, i;
	int boot_cpu_id = hard_smp_processor_id();

	for (cpu = 0; cpu < NR_CPUS; cpu++) {
		ia64_cpu_to_sapicid[cpu] = -1;
	}

	ia64_cpu_to_sapicid[0] = boot_cpu_id;
	init_cpu_present(cpumask_of(0));
	set_cpu_possible(0, true);
	for (cpu = 1, i = 0; i < smp_boot_data.cpu_count; i++) {
		sapicid = smp_boot_data.cpu_phys_id[i];
		if (sapicid == boot_cpu_id)
			continue;
		set_cpu_present(cpu, true);
		set_cpu_possible(cpu, true);
		ia64_cpu_to_sapicid[cpu] = sapicid;
		cpu++;
	}
}

/*
 * Cycle through the APs sending Wakeup IPIs to boot each.
 */
void __init
smp_prepare_cpus (unsigned int max_cpus)
{
	int boot_cpu_id = hard_smp_processor_id();

	/*
	 * Initialize the per-CPU profiling counter/multiplier
	 */

	smp_setup_percpu_timer();

	cpumask_set_cpu(0, &cpu_callin_map);

	local_cpu_data->loops_per_jiffy = loops_per_jiffy;
	ia64_cpu_to_sapicid[0] = boot_cpu_id;

	printk(KERN_INFO "Boot processor id 0x%x/0x%x\n", 0, boot_cpu_id);

	current_thread_info()->cpu = 0;

	/*
	 * If SMP should be disabled, then really disable it!
	 */
	if (!max_cpus) {
		printk(KERN_INFO "SMP mode deactivated.\n");
		init_cpu_online(cpumask_of(0));
		init_cpu_present(cpumask_of(0));
		init_cpu_possible(cpumask_of(0));
		return;
	}
}

void smp_prepare_boot_cpu(void)
{
	set_cpu_online(smp_processor_id(), true);
	cpumask_set_cpu(smp_processor_id(), &cpu_callin_map);
	set_numa_node(cpu_to_node_map[smp_processor_id()]);
	per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
}

#ifdef CONFIG_HOTPLUG_CPU
static inline void
clear_cpu_sibling_map(int cpu)
{
	int i;

	for_each_cpu(i, &per_cpu(cpu_sibling_map, cpu))
		cpumask_clear_cpu(cpu, &per_cpu(cpu_sibling_map, i));
	for_each_cpu(i, &cpu_core_map[cpu])
		cpumask_clear_cpu(cpu, &cpu_core_map[i]);

	per_cpu(cpu_sibling_map, cpu) = cpu_core_map[cpu] = CPU_MASK_NONE;
}

static void
remove_siblinginfo(int cpu)
{
	if (cpu_data(cpu)->threads_per_core == 1 &&
	    cpu_data(cpu)->cores_per_socket == 1) {
		cpumask_clear_cpu(cpu, &cpu_core_map[cpu]);
		cpumask_clear_cpu(cpu, &per_cpu(cpu_sibling_map, cpu));
		return;
	}

	/* remove it from all sibling map's */
	clear_cpu_sibling_map(cpu);
}

extern void fixup_irqs(void);

int migrate_platform_irqs(unsigned int cpu)
{
	int new_cpei_cpu;
	struct irq_data *data = NULL;
	const struct cpumask *mask;
	int 		retval = 0;

	/*
	 * dont permit CPEI target to removed.
	 */
	if (cpe_vector > 0 && is_cpu_cpei_target(cpu)) {
		printk ("CPU (%d) is CPEI Target\n", cpu);
		if (can_cpei_retarget()) {
			/*
			 * Now re-target the CPEI to a different processor
			 */
			new_cpei_cpu = cpumask_any(cpu_online_mask);
			mask = cpumask_of(new_cpei_cpu);
			set_cpei_target_cpu(new_cpei_cpu);
			data = irq_get_irq_data(ia64_cpe_irq);
			/*
			 * Switch for now, immediately, we need to do fake intr
			 * as other interrupts, but need to study CPEI behaviour with
			 * polling before making changes.
			 */
			if (data && data->chip) {
				data->chip->irq_disable(data);
				data->chip->irq_set_affinity(data, mask, false);
				data->chip->irq_enable(data);
				printk ("Re-targeting CPEI to cpu %d\n", new_cpei_cpu);
			}
		}
		if (!data) {
			printk ("Unable to retarget CPEI, offline cpu [%d] failed\n", cpu);
			retval = -EBUSY;
		}
	}
	return retval;
}

/* must be called with cpucontrol mutex held */
int __cpu_disable(void)
{
	int cpu = smp_processor_id();

	/*
	 * dont permit boot processor for now
	 */
	if (cpu == 0 && !bsp_remove_ok) {
		printk ("Your platform does not support removal of BSP\n");
		return (-EBUSY);
	}

	set_cpu_online(cpu, false);

	if (migrate_platform_irqs(cpu)) {
		set_cpu_online(cpu, true);
		return -EBUSY;
	}

	remove_siblinginfo(cpu);
	fixup_irqs();
	local_flush_tlb_all();
	cpumask_clear_cpu(cpu, &cpu_callin_map);
	return 0;
}

void __cpu_die(unsigned int cpu)
{
	unsigned int i;

	for (i = 0; i < 100; i++) {
		/* They ack this in play_dead by setting CPU_DEAD */
		if (per_cpu(cpu_state, cpu) == CPU_DEAD)
		{
			printk ("CPU %d is now offline\n", cpu);
			return;
		}
		msleep(100);
	}
 	printk(KERN_ERR "CPU %u didn't die...\n", cpu);
}
#endif /* CONFIG_HOTPLUG_CPU */

void
smp_cpus_done (unsigned int dummy)
{
	int cpu;
	unsigned long bogosum = 0;

	/*
	 * Allow the user to impress friends.
	 */

	for_each_online_cpu(cpu) {
		bogosum += cpu_data(cpu)->loops_per_jiffy;
	}

	printk(KERN_INFO "Total of %d processors activated (%lu.%02lu BogoMIPS).\n",
	       (int)num_online_cpus(), bogosum/(500000/HZ), (bogosum/(5000/HZ))%100);
}

static inline void set_cpu_sibling_map(int cpu)
{
	int i;

	for_each_online_cpu(i) {
		if ((cpu_data(cpu)->socket_id == cpu_data(i)->socket_id)) {
			cpumask_set_cpu(i, &cpu_core_map[cpu]);
			cpumask_set_cpu(cpu, &cpu_core_map[i]);
			if (cpu_data(cpu)->core_id == cpu_data(i)->core_id) {
				cpumask_set_cpu(i,
						&per_cpu(cpu_sibling_map, cpu));
				cpumask_set_cpu(cpu,
						&per_cpu(cpu_sibling_map, i));
			}
		}
	}
}

int
__cpu_up(unsigned int cpu, struct task_struct *tidle)
{
	int ret;
	int sapicid;

	sapicid = ia64_cpu_to_sapicid[cpu];
	if (sapicid == -1)
		return -EINVAL;

	/*
	 * Already booted cpu? not valid anymore since we dont
	 * do idle loop tightspin anymore.
	 */
	if (cpumask_test_cpu(cpu, &cpu_callin_map))
		return -EINVAL;

	per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
	/* Processor goes to start_secondary(), sets online flag */
	ret = do_boot_cpu(sapicid, cpu, tidle);
	if (ret < 0)
		return ret;

	if (cpu_data(cpu)->threads_per_core == 1 &&
	    cpu_data(cpu)->cores_per_socket == 1) {
		cpumask_set_cpu(cpu, &per_cpu(cpu_sibling_map, cpu));
		cpumask_set_cpu(cpu, &cpu_core_map[cpu]);
		return 0;
	}

	set_cpu_sibling_map(cpu);

	return 0;
}

/*
 * Assume that CPUs have been discovered by some platform-dependent interface.  For
 * SoftSDV/Lion, that would be ACPI.
 *
 * Setup of the IPI irq handler is done in irq.c:init_IRQ_SMP().
 */
void __init
init_smp_config(void)
{
	struct fptr {
		unsigned long fp;
		unsigned long gp;
	} *ap_startup;
	long sal_ret;

	/* Tell SAL where to drop the APs.  */
	ap_startup = (struct fptr *) start_ap;
	sal_ret = ia64_sal_set_vectors(SAL_VECTOR_OS_BOOT_RENDEZ,
				       ia64_tpa(ap_startup->fp), ia64_tpa(ap_startup->gp), 0, 0, 0, 0);
	if (sal_ret < 0)
		printk(KERN_ERR "SMP: Can't set SAL AP Boot Rendezvous: %s\n",
		       ia64_sal_strerror(sal_ret));
}

/*
 * identify_siblings(cpu) gets called from identify_cpu. This populates the 
 * information related to logical execution units in per_cpu_data structure.
 */
void identify_siblings(struct cpuinfo_ia64 *c)
{
	long status;
	u16 pltid;
	pal_logical_to_physical_t info;

	status = ia64_pal_logical_to_phys(-1, &info);
	if (status != PAL_STATUS_SUCCESS) {
		if (status != PAL_STATUS_UNIMPLEMENTED) {
			printk(KERN_ERR
				"ia64_pal_logical_to_phys failed with %ld\n",
				status);
			return;
		}

		info.overview_ppid = 0;
		info.overview_cpp  = 1;
		info.overview_tpc  = 1;
	}

	status = ia64_sal_physical_id_info(&pltid);
	if (status != PAL_STATUS_SUCCESS) {
		if (status != PAL_STATUS_UNIMPLEMENTED)
			printk(KERN_ERR
				"ia64_sal_pltid failed with %ld\n",
				status);
		return;
	}

	c->socket_id =  (pltid << 8) | info.overview_ppid;

	if (info.overview_cpp == 1 && info.overview_tpc == 1)
		return;

	c->cores_per_socket = info.overview_cpp;
	c->threads_per_core = info.overview_tpc;
	c->num_log = info.overview_num_log;

	c->core_id = info.log1_cid;
	c->thread_id = info.log1_tid;
}

/*
 * returns non zero, if multi-threading is enabled
 * on at least one physical package. Due to hotplug cpu
 * and (maxcpus=), all threads may not necessarily be enabled
 * even though the processor supports multi-threading.
 */
int is_multithreading_enabled(void)
{
	int i, j;

	for_each_present_cpu(i) {
		for_each_present_cpu(j) {
			if (j == i)
				continue;
			if ((cpu_data(j)->socket_id == cpu_data(i)->socket_id)) {
				if (cpu_data(j)->core_id == cpu_data(i)->core_id)
					return 1;
			}
		}
	}
	return 0;
}
EXPORT_SYMBOL_GPL(is_multithreading_enabled);