OpenCloudOS-Kernel/arch/x86/kernel/cpu/common.c

#include <linux/init.h>
#include <linux/string.h>
#include <linux/delay.h>
#include <linux/smp.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/bootmem.h>
#include <asm/processor.h>
#include <asm/i387.h>
#include <asm/msr.h>
#include <asm/io.h>
#include <asm/mmu_context.h>
#include <asm/mtrr.h>
#include <asm/mce.h>
#include <asm/pat.h>
#include <asm/asm.h>
#ifdef CONFIG_X86_LOCAL_APIC
#include <asm/mpspec.h>
#include <asm/apic.h>
#include <mach_apic.h>
#endif

#include "cpu.h"

DEFINE_PER_CPU(struct gdt_page, gdt_page) = { .gdt = {
	[GDT_ENTRY_KERNEL_CS] = { { { 0x0000ffff, 0x00cf9a00 } } },
	[GDT_ENTRY_KERNEL_DS] = { { { 0x0000ffff, 0x00cf9200 } } },
	[GDT_ENTRY_DEFAULT_USER_CS] = { { { 0x0000ffff, 0x00cffa00 } } },
	[GDT_ENTRY_DEFAULT_USER_DS] = { { { 0x0000ffff, 0x00cff200 } } },
	/*
	 * Segments used for calling PnP BIOS have byte granularity.
	 * They code segments and data segments have fixed 64k limits,
	 * the transfer segment sizes are set at run time.
	 */
	/* 32-bit code */
	[GDT_ENTRY_PNPBIOS_CS32] = { { { 0x0000ffff, 0x00409a00 } } },
	/* 16-bit code */
	[GDT_ENTRY_PNPBIOS_CS16] = { { { 0x0000ffff, 0x00009a00 } } },
	/* 16-bit data */
	[GDT_ENTRY_PNPBIOS_DS] = { { { 0x0000ffff, 0x00009200 } } },
	/* 16-bit data */
	[GDT_ENTRY_PNPBIOS_TS1] = { { { 0x00000000, 0x00009200 } } },
	/* 16-bit data */
	[GDT_ENTRY_PNPBIOS_TS2] = { { { 0x00000000, 0x00009200 } } },
	/*
	 * The APM segments have byte granularity and their bases
	 * are set at run time.  All have 64k limits.
	 */
	/* 32-bit code */
	[GDT_ENTRY_APMBIOS_BASE] = { { { 0x0000ffff, 0x00409a00 } } },
	/* 16-bit code */
	[GDT_ENTRY_APMBIOS_BASE+1] = { { { 0x0000ffff, 0x00009a00 } } },
	/* data */
	[GDT_ENTRY_APMBIOS_BASE+2] = { { { 0x0000ffff, 0x00409200 } } },

	[GDT_ENTRY_ESPFIX_SS] = { { { 0x00000000, 0x00c09200 } } },
	[GDT_ENTRY_PERCPU] = { { { 0x00000000, 0x00000000 } } },
} };
EXPORT_PER_CPU_SYMBOL_GPL(gdt_page);

__u32 cleared_cpu_caps[NCAPINTS] __cpuinitdata;

/* Current gdt points %fs at the "master" per-cpu area: after this,
 * it's on the real one. */
void switch_to_new_gdt(void)
{
	struct desc_ptr gdt_descr;

	gdt_descr.address = (long)get_cpu_gdt_table(smp_processor_id());
	gdt_descr.size = GDT_SIZE - 1;
	load_gdt(&gdt_descr);
	asm("mov %0, %%fs" : : "r" (__KERNEL_PERCPU) : "memory");
}

static int cachesize_override __cpuinitdata = -1;
static int disable_x86_serial_nr __cpuinitdata = 1;

struct cpu_dev *cpu_devs[X86_VENDOR_NUM] = {};

static void __cpuinit default_init(struct cpuinfo_x86 *c)
{
	/* Not much we can do here... */
	/* Check if at least it has cpuid */
	if (c->cpuid_level == -1) {
		/* No cpuid. It must be an ancient CPU */
		if (c->x86 == 4)
			strcpy(c->x86_model_id, "486");
		else if (c->x86 == 3)
			strcpy(c->x86_model_id, "386");
	}
}

static struct cpu_dev __cpuinitdata default_cpu = {
	.c_init	= default_init,
	.c_vendor = "Unknown",
};
static struct cpu_dev *this_cpu __cpuinitdata = &default_cpu;

static int __init cachesize_setup(char *str)
{
	get_option(&str, &cachesize_override);
	return 1;
}
__setup("cachesize=", cachesize_setup);

int __cpuinit get_model_name(struct cpuinfo_x86 *c)
{
	unsigned int *v;
	char *p, *q;

	if (c->extended_cpuid_level < 0x80000004)
		return 0;

	v = (unsigned int *) c->x86_model_id;
	cpuid(0x80000002, &v[0], &v[1], &v[2], &v[3]);
	cpuid(0x80000003, &v[4], &v[5], &v[6], &v[7]);
	cpuid(0x80000004, &v[8], &v[9], &v[10], &v[11]);
	c->x86_model_id[48] = 0;

	/* Intel chips right-justify this string for some dumb reason;
	   undo that brain damage */
	p = q = &c->x86_model_id[0];
	while (*p == ' ')
	     p++;
	if (p != q) {
	     while (*p)
		  *q++ = *p++;
	     while (q <= &c->x86_model_id[48])
		  *q++ = '\0';	/* Zero-pad the rest */
	}

	return 1;
}


void __cpuinit display_cacheinfo(struct cpuinfo_x86 *c)
{
	unsigned int n, dummy, ebx, ecx, edx, l2size;

	n = c->extended_cpuid_level;

	if (n >= 0x80000005) {
		cpuid(0x80000005, &dummy, &ebx, &ecx, &edx);
		printk(KERN_INFO "CPU: L1 I Cache: %dK (%d bytes/line), D cache %dK (%d bytes/line)\n",
				edx>>24, edx&0xFF, ecx>>24, ecx&0xFF);
		c->x86_cache_size = (ecx>>24) + (edx>>24);
	}

	if (n < 0x80000006)	/* Some chips just has a large L1. */
		return;

	ecx = cpuid_ecx(0x80000006);
	l2size = ecx >> 16;

	/* do processor-specific cache resizing */
	if (this_cpu->c_size_cache)
		l2size = this_cpu->c_size_cache(c, l2size);

	/* Allow user to override all this if necessary. */
	if (cachesize_override != -1)
		l2size = cachesize_override;

	if (l2size == 0)
		return;		/* Again, no L2 cache is possible */

	c->x86_cache_size = l2size;

	printk(KERN_INFO "CPU: L2 Cache: %dK (%d bytes/line)\n",
	       l2size, ecx & 0xFF);
}

/*
 * Naming convention should be: <Name> [(<Codename>)]
 * This table only is used unless init_<vendor>() below doesn't set it;
 * in particular, if CPUID levels 0x80000002..4 are supported, this isn't used
 *
 */

/* Look up CPU names by table lookup. */
static char __cpuinit *table_lookup_model(struct cpuinfo_x86 *c)
{
	struct cpu_model_info *info;

	if (c->x86_model >= 16)
		return NULL;	/* Range check */

	if (!this_cpu)
		return NULL;

	info = this_cpu->c_models;

	while (info && info->family) {
		if (info->family == c->x86)
			return info->model_names[c->x86_model];
		info++;
	}
	return NULL;		/* Not found */
}

#ifdef CONFIG_X86_HT
void __cpuinit detect_ht(struct cpuinfo_x86 *c)
{
	u32 	eax, ebx, ecx, edx;
	int 	index_msb, core_bits;

	cpuid(1, &eax, &ebx, &ecx, &edx);

	if (!cpu_has(c, X86_FEATURE_HT) || cpu_has(c, X86_FEATURE_CMP_LEGACY))
		return;

	smp_num_siblings = (ebx & 0xff0000) >> 16;

	if (smp_num_siblings == 1) {
		printk(KERN_INFO  "CPU: Hyper-Threading is disabled\n");
	} else if (smp_num_siblings > 1) {

		if (smp_num_siblings > NR_CPUS) {
			printk(KERN_WARNING "CPU: Unsupported number of siblings %d",
					smp_num_siblings);
			smp_num_siblings = 1;
			return;
		}

		index_msb = get_count_order(smp_num_siblings);
		c->phys_proc_id = phys_pkg_id(c->initial_apicid, index_msb);

		printk(KERN_INFO  "CPU: Physical Processor ID: %d\n",
		       c->phys_proc_id);

		smp_num_siblings = smp_num_siblings / c->x86_max_cores;

		index_msb = get_count_order(smp_num_siblings);

		core_bits = get_count_order(c->x86_max_cores);

		c->cpu_core_id = phys_pkg_id(c->initial_apicid, index_msb) &
					       ((1 << core_bits) - 1);

		if (c->x86_max_cores > 1)
			printk(KERN_INFO  "CPU: Processor Core ID: %d\n",
			       c->cpu_core_id);
	}
}
#endif

static void __cpuinit get_cpu_vendor(struct cpuinfo_x86 *c)
{
	char *v = c->x86_vendor_id;
	int i;
	static int printed;

	for (i = 0; i < X86_VENDOR_NUM; i++) {
		if (cpu_devs[i]) {
			if (!strcmp(v, cpu_devs[i]->c_ident[0]) ||
			    (cpu_devs[i]->c_ident[1] &&
			     !strcmp(v, cpu_devs[i]->c_ident[1]))) {
				c->x86_vendor = i;
				this_cpu = cpu_devs[i];
				return;
			}
		}
	}
	if (!printed) {
		printed++;
		printk(KERN_ERR "CPU: Vendor unknown, using generic init.\n");
		printk(KERN_ERR "CPU: Your system may be unstable.\n");
	}
	c->x86_vendor = X86_VENDOR_UNKNOWN;
	this_cpu = &default_cpu;
}


static int __init x86_fxsr_setup(char *s)
{
	setup_clear_cpu_cap(X86_FEATURE_FXSR);
	setup_clear_cpu_cap(X86_FEATURE_XMM);
	return 1;
}
__setup("nofxsr", x86_fxsr_setup);


static int __init x86_sep_setup(char *s)
{
	setup_clear_cpu_cap(X86_FEATURE_SEP);
	return 1;
}
__setup("nosep", x86_sep_setup);


/* Standard macro to see if a specific flag is changeable */
static inline int flag_is_changeable_p(u32 flag)
{
	u32 f1, f2;

	asm("pushfl\n\t"
	    "pushfl\n\t"
	    "popl %0\n\t"
	    "movl %0,%1\n\t"
	    "xorl %2,%0\n\t"
	    "pushl %0\n\t"
	    "popfl\n\t"
	    "pushfl\n\t"
	    "popl %0\n\t"
	    "popfl\n\t"
	    : "=&r" (f1), "=&r" (f2)
	    : "ir" (flag));

	return ((f1^f2) & flag) != 0;
}


/* Probe for the CPUID instruction */
static int __cpuinit have_cpuid_p(void)
{
	return flag_is_changeable_p(X86_EFLAGS_ID);
}

static void __init early_cpu_support_print(void)
{
	int i,j;
	struct cpu_dev *cpu_devx;

	printk("KERNEL supported cpus:\n");
	for (i = 0; i < X86_VENDOR_NUM; i++) {
		cpu_devx = cpu_devs[i];
		if (!cpu_devx)
			continue;
		for (j = 0; j < 2; j++) {
			if (!cpu_devx->c_ident[j])
				continue;
			printk("  %s %s\n", cpu_devx->c_vendor,
				cpu_devx->c_ident[j]);
		}
	}
}

void __cpuinit cpu_detect(struct cpuinfo_x86 *c)
{
	/* Get vendor name */
	cpuid(0x00000000, (unsigned int *)&c->cpuid_level,
	      (unsigned int *)&c->x86_vendor_id[0],
	      (unsigned int *)&c->x86_vendor_id[8],
	      (unsigned int *)&c->x86_vendor_id[4]);

	c->x86 = 4;
	/* Intel-defined flags: level 0x00000001 */
	if (c->cpuid_level >= 0x00000001) {
		u32 junk, tfms, cap0, misc;
		cpuid(0x00000001, &tfms, &misc, &junk, &cap0);
		c->x86 = (tfms >> 8) & 0xf;
		c->x86_model = (tfms >> 4) & 0xf;
		c->x86_mask = tfms & 0xf;
		if (c->x86 == 0xf)
			c->x86 += (tfms >> 20) & 0xff;
		if (c->x86 >= 0x6)
			c->x86_model += ((tfms >> 16) & 0xf) << 4;
		if (cap0 & (1<<19)) {
			c->x86_clflush_size = ((misc >> 8) & 0xff) * 8;
			c->x86_cache_alignment = c->x86_clflush_size;
		}
	}
}

static void __cpuinit get_cpu_cap(struct cpuinfo_x86 *c)
{
	u32 tfms, xlvl;
	u32 ebx;

	/* Intel-defined flags: level 0x00000001 */
	if (c->cpuid_level >= 0x00000001) {
		u32 capability, excap;
		cpuid(0x00000001, &tfms, &ebx, &excap, &capability);
		c->x86_capability[0] = capability;
		c->x86_capability[4] = excap;
	}

	/* AMD-defined flags: level 0x80000001 */
	xlvl = cpuid_eax(0x80000000);
	c->extended_cpuid_level = xlvl;
	if ((xlvl & 0xffff0000) == 0x80000000) {
		if (xlvl >= 0x80000001) {
			c->x86_capability[1] = cpuid_edx(0x80000001);
			c->x86_capability[6] = cpuid_ecx(0x80000001);
		}
	}
}
/*
 * Do minimum CPU detection early.
 * Fields really needed: vendor, cpuid_level, family, model, mask,
 * cache alignment.
 * The others are not touched to avoid unwanted side effects.
 *
 * WARNING: this function is only called on the BP.  Don't add code here
 * that is supposed to run on all CPUs.
 */
static void __init early_identify_cpu(struct cpuinfo_x86 *c)
{
	c->x86_cache_alignment = 32;
	c->x86_clflush_size = 32;

	if (!have_cpuid_p())
		return;

	c->extended_cpuid_level = 0;

	memset(&c->x86_capability, 0, sizeof c->x86_capability);

	cpu_detect(c);

	get_cpu_vendor(c);

	get_cpu_cap(c);

	if (c->x86_vendor != X86_VENDOR_UNKNOWN &&
	    cpu_devs[c->x86_vendor]->c_early_init)
		cpu_devs[c->x86_vendor]->c_early_init(c);

	validate_pat_support(c);
}

void __init early_cpu_init(void)
{
	struct cpu_vendor_dev *cvdev;

	for (cvdev = __x86cpuvendor_start; cvdev < __x86cpuvendor_end; cvdev++)
		cpu_devs[cvdev->vendor] = cvdev->cpu_dev;

	early_cpu_support_print();
	early_identify_cpu(&boot_cpu_data);
}

/*
 * The NOPL instruction is supposed to exist on all CPUs with
 * family >= 6, unfortunately, that's not true in practice because
 * of early VIA chips and (more importantly) broken virtualizers that
 * are not easy to detect.  Hence, probe for it based on first
 * principles.
 */
static void __cpuinit detect_nopl(struct cpuinfo_x86 *c)
{
	const u32 nopl_signature = 0x888c53b1; /* Random number */
	u32 has_nopl = nopl_signature;

	clear_cpu_cap(c, X86_FEATURE_NOPL);
	if (c->x86 >= 6) {
		asm volatile("\n"
			     "1:      .byte 0x0f,0x1f,0xc0\n" /* nopl %eax */
			     "2:\n"
			     "        .section .fixup,\"ax\"\n"
			     "3:      xor %0,%0\n"
			     "        jmp 2b\n"
			     "        .previous\n"
			     _ASM_EXTABLE(1b,3b)
			     : "+a" (has_nopl));

		if (has_nopl == nopl_signature)
			set_cpu_cap(c, X86_FEATURE_NOPL);
	}
}

static void __cpuinit generic_identify(struct cpuinfo_x86 *c)
{
	if (!have_cpuid_p())
		return;

	c->extended_cpuid_level = 0;

	cpu_detect(c);

	get_cpu_vendor(c);

	get_cpu_cap(c);

	if (c->cpuid_level >= 0x00000001) {
		c->initial_apicid = (cpuid_ebx(1) >> 24) & 0xFF;
#ifdef CONFIG_X86_HT
		c->apicid = phys_pkg_id(c->initial_apicid, 0);
		c->phys_proc_id = c->initial_apicid;
#else
		c->apicid = c->initial_apicid;
#endif
	}

	if (c->extended_cpuid_level >= 0x80000004)
		get_model_name(c); /* Default name */

	init_scattered_cpuid_features(c);
	detect_nopl(c);
}

static void __cpuinit squash_the_stupid_serial_number(struct cpuinfo_x86 *c)
{
	if (cpu_has(c, X86_FEATURE_PN) && disable_x86_serial_nr) {
		/* Disable processor serial number */
		unsigned long lo, hi;
		rdmsr(MSR_IA32_BBL_CR_CTL, lo, hi);
		lo |= 0x200000;
		wrmsr(MSR_IA32_BBL_CR_CTL, lo, hi);
		printk(KERN_NOTICE "CPU serial number disabled.\n");
		clear_cpu_cap(c, X86_FEATURE_PN);

		/* Disabling the serial number may affect the cpuid level */
		c->cpuid_level = cpuid_eax(0);
	}
}

static int __init x86_serial_nr_setup(char *s)
{
	disable_x86_serial_nr = 0;
	return 1;
}
__setup("serialnumber", x86_serial_nr_setup);



/*
 * This does the hard work of actually picking apart the CPU stuff...
 */
static void __cpuinit identify_cpu(struct cpuinfo_x86 *c)
{
	int i;

	c->loops_per_jiffy = loops_per_jiffy;
	c->x86_cache_size = -1;
	c->x86_vendor = X86_VENDOR_UNKNOWN;
	c->cpuid_level = -1;	/* CPUID not detected */
	c->x86_model = c->x86_mask = 0;	/* So far unknown... */
	c->x86_vendor_id[0] = '\0'; /* Unset */
	c->x86_model_id[0] = '\0';  /* Unset */
	c->x86_max_cores = 1;
	c->x86_clflush_size = 32;
	memset(&c->x86_capability, 0, sizeof c->x86_capability);

	if (!have_cpuid_p()) {
		/*
		 * First of all, decide if this is a 486 or higher
		 * It's a 486 if we can modify the AC flag
		 */
		if (flag_is_changeable_p(X86_EFLAGS_AC))
			c->x86 = 4;
		else
			c->x86 = 3;
	}

	generic_identify(c);

	if (this_cpu->c_identify)
		this_cpu->c_identify(c);

	/*
	 * Vendor-specific initialization.  In this section we
	 * canonicalize the feature flags, meaning if there are
	 * features a certain CPU supports which CPUID doesn't
	 * tell us, CPUID claiming incorrect flags, or other bugs,
	 * we handle them here.
	 *
	 * At the end of this section, c->x86_capability better
	 * indicate the features this CPU genuinely supports!
	 */
	if (this_cpu->c_init)
		this_cpu->c_init(c);

	/* Disable the PN if appropriate */
	squash_the_stupid_serial_number(c);

	/*
	 * The vendor-specific functions might have changed features.  Now
	 * we do "generic changes."
	 */

	/* If the model name is still unset, do table lookup. */
	if (!c->x86_model_id[0]) {
		char *p;
		p = table_lookup_model(c);
		if (p)
			strcpy(c->x86_model_id, p);
		else
			/* Last resort... */
			sprintf(c->x86_model_id, "%02x/%02x",
				c->x86, c->x86_model);
	}

	/*
	 * On SMP, boot_cpu_data holds the common feature set between
	 * all CPUs; so make sure that we indicate which features are
	 * common between the CPUs.  The first time this routine gets
	 * executed, c == &boot_cpu_data.
	 */
	if (c != &boot_cpu_data) {
		/* AND the already accumulated flags with these */
		for (i = 0; i < NCAPINTS; i++)
			boot_cpu_data.x86_capability[i] &= c->x86_capability[i];
	}

	/* Clear all flags overriden by options */
	for (i = 0; i < NCAPINTS; i++)
		c->x86_capability[i] &= ~cleared_cpu_caps[i];

	/* Init Machine Check Exception if available. */
	mcheck_init(c);

	select_idle_routine(c);
}

void __init identify_boot_cpu(void)
{
	identify_cpu(&boot_cpu_data);
	sysenter_setup();
	enable_sep_cpu();
}

void __cpuinit identify_secondary_cpu(struct cpuinfo_x86 *c)
{
	BUG_ON(c == &boot_cpu_data);
	identify_cpu(c);
	enable_sep_cpu();
	mtrr_ap_init();
}

static __init int setup_noclflush(char *arg)
{
	setup_clear_cpu_cap(X86_FEATURE_CLFLSH);
	return 1;
}
__setup("noclflush", setup_noclflush);

void __cpuinit print_cpu_info(struct cpuinfo_x86 *c)
{
	char *vendor = NULL;

	if (c->x86_vendor < X86_VENDOR_NUM)
		vendor = this_cpu->c_vendor;
	else if (c->cpuid_level >= 0)
		vendor = c->x86_vendor_id;

	if (vendor && strncmp(c->x86_model_id, vendor, strlen(vendor)))
		printk(KERN_CONT "%s ", vendor);

	if (c->x86_model_id[0])
		printk(KERN_CONT "%s", c->x86_model_id);
	else
		printk(KERN_CONT "%d86", c->x86);

	if (c->x86_mask || c->cpuid_level >= 0)
		printk(KERN_CONT " stepping %02x\n", c->x86_mask);
	else
		printk(KERN_CONT "\n");
}

static __init int setup_disablecpuid(char *arg)
{
	int bit;
	if (get_option(&arg, &bit) && bit < NCAPINTS*32)
		setup_clear_cpu_cap(bit);
	else
		return 0;
	return 1;
}
__setup("clearcpuid=", setup_disablecpuid);

cpumask_t cpu_initialized __cpuinitdata = CPU_MASK_NONE;

/* Make sure %fs is initialized properly in idle threads */
struct pt_regs * __cpuinit idle_regs(struct pt_regs *regs)
{
	memset(regs, 0, sizeof(struct pt_regs));
	regs->fs = __KERNEL_PERCPU;
	return regs;
}

/*
 * cpu_init() initializes state that is per-CPU. Some data is already
 * initialized (naturally) in the bootstrap process, such as the GDT
 * and IDT. We reload them nevertheless, this function acts as a
 * 'CPU state barrier', nothing should get across.
 */
void __cpuinit cpu_init(void)
{
	int cpu = smp_processor_id();
	struct task_struct *curr = current;
	struct tss_struct *t = &per_cpu(init_tss, cpu);
	struct thread_struct *thread = &curr->thread;

	if (cpu_test_and_set(cpu, cpu_initialized)) {
		printk(KERN_WARNING "CPU#%d already initialized!\n", cpu);
		for (;;) local_irq_enable();
	}

	printk(KERN_INFO "Initializing CPU#%d\n", cpu);

	if (cpu_has_vme || cpu_has_tsc || cpu_has_de)
		clear_in_cr4(X86_CR4_VME|X86_CR4_PVI|X86_CR4_TSD|X86_CR4_DE);

	load_idt(&idt_descr);
	switch_to_new_gdt();

	/*
	 * Set up and load the per-CPU TSS and LDT
	 */
	atomic_inc(&init_mm.mm_count);
	curr->active_mm = &init_mm;
	if (curr->mm)
		BUG();
	enter_lazy_tlb(&init_mm, curr);

	load_sp0(t, thread);
	set_tss_desc(cpu, t);
	load_TR_desc();
	load_LDT(&init_mm.context);

#ifdef CONFIG_DOUBLEFAULT
	/* Set up doublefault TSS pointer in the GDT */
	__set_tss_desc(cpu, GDT_ENTRY_DOUBLEFAULT_TSS, &doublefault_tss);
#endif

	/* Clear %gs. */
	asm volatile ("mov %0, %%gs" : : "r" (0));

	/* Clear all 6 debug registers: */
	set_debugreg(0, 0);
	set_debugreg(0, 1);
	set_debugreg(0, 2);
	set_debugreg(0, 3);
	set_debugreg(0, 6);
	set_debugreg(0, 7);

	/*
	 * Force FPU initialization:
	 */
	current_thread_info()->status = 0;
	clear_used_math();
	mxcsr_feature_mask_init();
}

#ifdef CONFIG_HOTPLUG_CPU
void __cpuinit cpu_uninit(void)
{
	int cpu = raw_smp_processor_id();
	cpu_clear(cpu, cpu_initialized);

	/* lazy TLB state */
	per_cpu(cpu_tlbstate, cpu).state = 0;
	per_cpu(cpu_tlbstate, cpu).active_mm = &init_mm;
}
#endif