path: root/arch/powerpc/platforms/pseries/xics.c

/*
 * arch/powerpc/platforms/pseries/xics.c
 *
 * Copyright 2000 IBM Corporation.
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/types.h>
#include <linux/threads.h>
#include <linux/kernel.h>
#include <linux/irq.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/init.h>
#include <linux/radix-tree.h>
#include <linux/cpu.h>
#include <linux/of.h>

#include <asm/firmware.h>
#include <asm/io.h>
#include <asm/pgtable.h>
#include <asm/smp.h>
#include <asm/rtas.h>
#include <asm/hvcall.h>
#include <asm/machdep.h>

#include "xics.h"
#include "plpar_wrappers.h"

static struct irq_host *xics_host;

#define XICS_IPI		2
#define XICS_IRQ_SPURIOUS	0

/* Want a priority other than 0.  Various HW issues require this. */
#define	DEFAULT_PRIORITY	5

/*
 * Mark IPIs as higher priority so we can take them inside interrupts that
 * arent marked IRQF_DISABLED
 */
#define IPI_PRIORITY		4

static unsigned int default_server = 0xFF;
static unsigned int default_distrib_server = 0;
static unsigned int interrupt_server_size = 8;

/* RTAS service tokens */
static int ibm_get_xive;
static int ibm_set_xive;
static int ibm_int_on;
static int ibm_int_off;


/* Direct hardware low level accessors */

/* The part of the interrupt presentation layer that we care about */
struct xics_ipl {
	union {
		u32 word;
		u8 bytes[4];
	} xirr_poll;
	union {
		u32 word;
		u8 bytes[4];
	} xirr;
	u32 dummy;
	union {
		u32 word;
		u8 bytes[4];
	} qirr;
};

static struct xics_ipl __iomem *xics_per_cpu[NR_CPUS];

static inline unsigned int direct_xirr_info_get(void)
{
	int cpu = smp_processor_id();

	return in_be32(&xics_per_cpu[cpu]->xirr.word);
}

static inline void direct_xirr_info_set(unsigned int value)
{
	int cpu = smp_processor_id();

	out_be32(&xics_per_cpu[cpu]->xirr.word, value);
}

static inline void direct_cppr_info(u8 value)
{
	int cpu = smp_processor_id();

	out_8(&xics_per_cpu[cpu]->xirr.bytes[0], value);
}

static inline void direct_qirr_info(int n_cpu, u8 value)
{
	out_8(&xics_per_cpu[n_cpu]->qirr.bytes[0], value);
}


/* LPAR low level accessors */

static inline unsigned int lpar_xirr_info_get(void)
{
	unsigned long lpar_rc;
	unsigned long return_value;

	lpar_rc = plpar_xirr(&return_value);
	if (lpar_rc != H_SUCCESS)
		panic(" bad return code xirr - rc = %lx \n", lpar_rc);
	return (unsigned int)return_value;
}

static inline void lpar_xirr_info_set(unsigned int value)
{
	unsigned long lpar_rc;

	lpar_rc = plpar_eoi(value);
	if (lpar_rc != H_SUCCESS)
		panic("bad return code EOI - rc = %ld, value=%x\n", lpar_rc,
		      value);
}

static inline void lpar_cppr_info(u8 value)
{
	unsigned long lpar_rc;

	lpar_rc = plpar_cppr(value);
	if (lpar_rc != H_SUCCESS)
		panic("bad return code cppr - rc = %lx\n", lpar_rc);
}

static inline void lpar_qirr_info(int n_cpu , u8 value)
{
	unsigned long lpar_rc;

	lpar_rc = plpar_ipi(get_hard_smp_processor_id(n_cpu), value);
	if (lpar_rc != H_SUCCESS)
		panic("bad return code qirr - rc = %lx\n", lpar_rc);
}


/* Interface to generic irq subsystem */

#ifdef CONFIG_SMP
static int get_irq_server(unsigned int virq, unsigned int strict_check)
{
	int server;
	/* For the moment only implement delivery to all cpus or one cpu */
	cpumask_t cpumask = irq_desc[virq].affinity;
	cpumask_t tmp = CPU_MASK_NONE;

	if (!distribute_irqs)
		return default_server;

	if (!cpus_equal(cpumask, CPU_MASK_ALL)) {
		cpus_and(tmp, cpu_online_map, cpumask);

		server = first_cpu(tmp);

		if (server < NR_CPUS)
			return get_hard_smp_processor_id(server);

		if (strict_check)
			return -1;
	}

	if (cpus_equal(cpu_online_map, cpu_present_map))
		return default_distrib_server;

	return default_server;
}
#else
static int get_irq_server(unsigned int virq, unsigned int strict_check)
{
	return default_server;
}
#endif

static void xics_unmask_irq(unsigned int virq)
{
	unsigned int irq;
	int call_status;
	int server;

	pr_debug("xics: unmask virq %d\n", virq);

	irq = (unsigned int)irq_map[virq].hwirq;
	pr_debug(" -> map to hwirq 0x%x\n", irq);
	if (irq == XICS_IPI || irq == XICS_IRQ_SPURIOUS)
		return;

	server = get_irq_server(virq, 0);

	call_status = rtas_call(ibm_set_xive, 3, 1, NULL, irq, server,
				DEFAULT_PRIORITY);
	if (call_status != 0) {
		printk(KERN_ERR
			"%s: ibm_set_xive irq %u server %x returned %d\n",
			__func__, irq, server, call_status);
		return;
	}

	/* Now unmask the interrupt (often a no-op) */
	call_status = rtas_call(ibm_int_on, 1, 1, NULL, irq);
	if (call_status != 0) {
		printk(KERN_ERR "%s: ibm_int_on irq=%u returned %d\n",
			__func__, irq, call_status);
		return;
	}
}

static unsigned int xics_startup(unsigned int virq)
{
	/* unmask it */
	xics_unmask_irq(virq);
	return 0;
}

static void xics_mask_real_irq(unsigned int irq)
{
	int call_status;

	if (irq == XICS_IPI)
		return;

	call_status = rtas_call(ibm_int_off, 1, 1, NULL, irq);
	if (call_status != 0) {
		printk(KERN_ERR "%s: ibm_int_off irq=%u returned %d\n",
			__func__, irq, call_status);
		return;
	}

	/* Have to set XIVE to 0xff to be able to remove a slot */
	call_status = rtas_call(ibm_set_xive, 3, 1, NULL, irq,
				default_server, 0xff);
	if (call_status != 0) {
		printk(KERN_ERR "%s: ibm_set_xive(0xff) irq=%u returned %d\n",
			__func__, irq, call_status);
		return;
	}
}

static void xics_mask_irq(unsigned int virq)
{
	unsigned int irq;

	pr_debug("xics: mask virq %d\n", virq);

	irq = (unsigned int)irq_map[virq].hwirq;
	if (irq == XICS_IPI || irq == XICS_IRQ_SPURIOUS)
		return;
	xics_mask_real_irq(irq);
}

static void xics_mask_unknown_vec(unsigned int vec)
{
	printk(KERN_ERR "Interrupt %u (real) is invalid, disabling it.\n", vec);
	xics_mask_real_irq(vec);
}

static inline unsigned int xics_xirr_vector(unsigned int xirr)
{
	/*
	 * The top byte is the old cppr, to be restored on EOI.
	 * The remaining 24 bits are the vector.
	 */
	return xirr & 0x00ffffff;
}

static unsigned int xics_get_irq_direct(void)
{
	unsigned int xirr = direct_xirr_info_get();
	unsigned int vec = xics_xirr_vector(xirr);
	unsigned int irq;

	if (vec == XICS_IRQ_SPURIOUS)
		return NO_IRQ;

	irq = irq_radix_revmap_lookup(xics_host, vec);
	if (likely(irq != NO_IRQ))
		return irq;

	/* We don't have a linux mapping, so have rtas mask it. */
	xics_mask_unknown_vec(vec);

	/* We might learn about it later, so EOI it */
	direct_xirr_info_set(xirr);
	return NO_IRQ;
}

static unsigned int xics_get_irq_lpar(void)
{
	unsigned int xirr = lpar_xirr_info_get();
	unsigned int vec = xics_xirr_vector(xirr);
	unsigned int irq;

	if (vec == XICS_IRQ_SPURIOUS)
		return NO_IRQ;

	irq = irq_radix_revmap_lookup(xics_host, vec);
	if (likely(irq != NO_IRQ))
		return irq;

	/* We don't have a linux mapping, so have RTAS mask it. */
	xics_mask_unknown_vec(vec);

	/* We might learn about it later, so EOI it */
	lpar_xirr_info_set(xirr);
	return NO_IRQ;
}

static void xics_eoi_direct(unsigned int virq)
{
	unsigned int irq = (unsigned int)irq_map[virq].hwirq;

	iosync();
	direct_xirr_info_set((0xff << 24) | irq);
}

static void xics_eoi_lpar(unsigned int virq)
{
	unsigned int irq = (unsigned int)irq_map[virq].hwirq;

	iosync();
	lpar_xirr_info_set((0xff << 24) | irq);
}

static void xics_set_affinity(unsigned int virq, cpumask_t cpumask)
{
	unsigned int irq;
	int status;
	int xics_status[2];
	int irq_server;

	irq = (unsigned int)irq_map[virq].hwirq;
	if (irq == XICS_IPI || irq == XICS_IRQ_SPURIOUS)
		return;

	status = rtas_call(ibm_get_xive, 1, 3, xics_status, irq);

	if (status) {
		printk(KERN_ERR "%s: ibm,get-xive irq=%u returns %d\n",
			__func__, irq, status);
		return;
	}

	/*
	 * For the moment only implement delivery to all cpus or one cpu.
	 * Get current irq_server for the given irq
	 */
	irq_server = get_irq_server(virq, 1);
	if (irq_server == -1) {
		char cpulist[128];
		cpumask_scnprintf(cpulist, sizeof(cpulist), &cpumask);
		printk(KERN_WARNING
			"%s: No online cpus in the mask %s for irq %d\n",
			__func__, cpulist, virq);
		return;
	}

	status = rtas_call(ibm_set_xive, 3, 1, NULL,
				irq, irq_server, xics_status[1]);

	if (status) {
		printk(KERN_ERR "%s: ibm,set-xive irq=%u returns %d\n",
			__func__, irq, status);
		return;
	}
}

static struct irq_chip xics_pic_direct = {
	.typename = " XICS     ",
	.startup = xics_startup,
	.mask = xics_mask_irq,
	.unmask = xics_unmask_irq,
	.eoi = xics_eoi_direct,
	.set_affinity = xics_set_affinity
};

static struct irq_chip xics_pic_lpar = {
	.typename = " XICS     ",
	.startup = xics_startup,
	.mask = xics_mask_irq,
	.unmask = xics_unmask_irq,
	.eoi = xics_eoi_lpar,
	.set_affinity = xics_set_affinity
};


/* Interface to arch irq controller subsystem layer */

/* Points to the irq_chip we're actually using */
static struct irq_chip *xics_irq_chip;

static int xics_host_match(struct irq_host *h, struct device_node *node)
{
	/* IBM machines have interrupt parents of various funky types for things
	 * like vdevices, events, etc... The trick we use here is to match
	 * everything here except the legacy 8259 which is compatible "chrp,iic"
	 */
	return !of_device_is_compatible(node, "chrp,iic");
}

static int xics_host_map(struct irq_host *h, unsigned int virq,
			 irq_hw_number_t hw)
{
	pr_debug("xics: map virq %d, hwirq 0x%lx\n", virq, hw);

	/* Insert the interrupt mapping into the radix tree for fast lookup */
	irq_radix_revmap_insert(xics_host, virq, hw);

	get_irq_desc(virq)->status |= IRQ_LEVEL;
	set_irq_chip_and_handler(virq, xics_irq_chip, handle_fasteoi_irq);
	return 0;
}

static int xics_host_xlate(struct irq_host *h, struct device_node *ct,
			   u32 *intspec, unsigned int intsize,
			   irq_hw_number_t *out_hwirq, unsigned int *out_flags)

{
	/* Current xics implementation translates everything
	 * to level. It is not technically right for MSIs but this
	 * is irrelevant at this point. We might get smarter in the future
	 */
	*out_hwirq = intspec[0];
	*out_flags = IRQ_TYPE_LEVEL_LOW;

	return 0;
}

static struct irq_host_ops xics_host_ops = {
	.match = xics_host_match,
	.map = xics_host_map,
	.xlate = xics_host_xlate,
};

static void __init xics_init_host(void)
{
	if (firmware_has_feature(FW_FEATURE_LPAR))
		xics_irq_chip = &xics_pic_lpar;
	else
		xics_irq_chip = &xics_pic_direct;

	xics_host = irq_alloc_host(NULL, IRQ_HOST_MAP_TREE, 0, &xics_host_ops,
				   XICS_IRQ_SPURIOUS);
	BUG_ON(xics_host == NULL);
	irq_set_default_host(xics_host);
}


/* Inter-processor interrupt support */

#ifdef CONFIG_SMP
/*
 * XICS only has a single IPI, so encode the messages per CPU
 */
struct xics_ipi_struct {
        unsigned long value;
	} ____cacheline_aligned;

static struct xics_ipi_struct xics_ipi_message[NR_CPUS] __cacheline_aligned;

static inline void smp_xics_do_message(int cpu, int msg)
{
	set_bit(msg, &xics_ipi_message[cpu].value);
	mb();
	if (firmware_has_feature(FW_FEATURE_LPAR))
		lpar_qirr_info(cpu, IPI_PRIORITY);
	else
		direct_qirr_info(cpu, IPI_PRIORITY);
}

void smp_xics_message_pass(int target, int msg)
{
	unsigned int i;

	if (target < NR_CPUS) {
		smp_xics_do_message(target, msg);
	} else {
		for_each_online_cpu(i) {
			if (target == MSG_ALL_BUT_SELF
			    && i == smp_processor_id())
				continue;
			smp_xics_do_message(i, msg);
		}
	}
}

static irqreturn_t xics_ipi_dispatch(int cpu)
{
	WARN_ON(cpu_is_offline(cpu));

	mb();	/* order mmio clearing qirr */
	while (xics_ipi_message[cpu].value) {
		if (test_and_clear_bit(PPC_MSG_CALL_FUNCTION,
				       &xics_ipi_message[cpu].value)) {
			smp_message_recv(PPC_MSG_CALL_FUNCTION);
		}
		if (test_and_clear_bit(PPC_MSG_RESCHEDULE,
				       &xics_ipi_message[cpu].value)) {
			smp_message_recv(PPC_MSG_RESCHEDULE);
		}
		if (test_and_clear_bit(PPC_MSG_CALL_FUNC_SINGLE,
				       &xics_ipi_message[cpu].value)) {
			smp_message_recv(PPC_MSG_CALL_FUNC_SINGLE);
		}
#if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC)
		if (test_and_clear_bit(PPC_MSG_DEBUGGER_BREAK,
				       &xics_ipi_message[cpu].value)) {
			smp_message_recv(PPC_MSG_DEBUGGER_BREAK);
		}
#endif
	}
	return IRQ_HANDLED;
}

static irqreturn_t xics_ipi_action_direct(int irq, void *dev_id)
{
	int cpu = smp_processor_id();

	direct_qirr_info(cpu, 0xff);

	return xics_ipi_dispatch(cpu);
}

static irqreturn_t xics_ipi_action_lpar(int irq, void *dev_id)
{
	int cpu = smp_processor_id();

	lpar_qirr_info(cpu, 0xff);

	return xics_ipi_dispatch(cpu);
}

static void xics_request_ipi(void)
{
	unsigned int ipi;
	int rc;

	ipi = irq_create_mapping(xics_host, XICS_IPI);
	BUG_ON(ipi == NO_IRQ);

	/*
	 * IPIs are marked IRQF_DISABLED as they must run with irqs
	 * disabled
	 */
	set_irq_handler(ipi, handle_percpu_irq);
	if (firmware_has_feature(FW_FEATURE_LPAR))
		rc = request_irq(ipi, xics_ipi_action_lpar,
				IRQF_DISABLED|IRQF_PERCPU, "IPI", NULL);
	else
		rc = request_irq(ipi, xics_ipi_action_direct,
				IRQF_DISABLED|IRQF_PERCPU, "IPI", NULL);
	BUG_ON(rc);
}

int __init smp_xics_probe(void)
{
	xics_request_ipi();

	return cpus_weight(cpu_possible_map);
}

#endif /* CONFIG_SMP */


/* Initialization */

static void xics_update_irq_servers(void)
{
	int i, j;
	struct device_node *np;
	u32 ilen;
	const u32 *ireg, *isize;
	u32 hcpuid;

	/* Find the server numbers for the boot cpu. */
	np = of_get_cpu_node(boot_cpuid, NULL);
	BUG_ON(!np);

	ireg = of_get_property(np, "ibm,ppc-interrupt-gserver#s", &ilen);
	if (!ireg) {
		of_node_put(np);
		return;
	}

	i = ilen / sizeof(int);
	hcpuid = get_hard_smp_processor_id(boot_cpuid);

	/* Global interrupt distribution server is specified in the last
	 * entry of "ibm,ppc-interrupt-gserver#s" property. Get the last
	 * entry fom this property for current boot cpu id and use it as
	 * default distribution server
	 */
	for (j = 0; j < i; j += 2) {
		if (ireg[j] == hcpuid) {
			default_server = hcpuid;
			default_distrib_server = ireg[j+1];
		}
	}

	/* get the bit size of server numbers */
	isize = of_get_property(np, "ibm,interrupt-server#-size", NULL);
	if (isize)
		interrupt_server_size = *isize;

	of_node_put(np);
}

static void __init xics_map_one_cpu(int hw_id, unsigned long addr,
				     unsigned long size)
{
	int i;

	/* This may look gross but it's good enough for now, we don't quite
	 * have a hard -> linux processor id matching.
	 */
	for_each_possible_cpu(i) {
		if (!cpu_present(i))
			continue;
		if (hw_id == get_hard_smp_processor_id(i)) {
			xics_per_cpu[i] = ioremap(addr, size);
			return;
		}
	}
}

static void __init xics_init_one_node(struct device_node *np,
				      unsigned int *indx)
{
	unsigned int ilen;
	const u32 *ireg;

	/* This code does the theorically broken assumption that the interrupt
	 * server numbers are the same as the hard CPU numbers.
	 * This happens to be the case so far but we are playing with fire...
	 * should be fixed one of these days. -BenH.
	 */
	ireg = of_get_property(np, "ibm,interrupt-server-ranges", NULL);

	/* Do that ever happen ? we'll know soon enough... but even good'old
	 * f80 does have that property ..
	 */
	WARN_ON(ireg == NULL);
	if (ireg) {
		/*
		 * set node starting index for this node
		 */
		*indx = *ireg;
	}
	ireg = of_get_property(np, "reg", &ilen);
	if (!ireg)
		panic("xics_init_IRQ: can't find interrupt reg property");

	while (ilen >= (4 * sizeof(u32))) {
		unsigned long addr, size;

		/* XXX Use proper OF parsing code here !!! */
		addr = (unsigned long)*ireg++ << 32;
		ilen -= sizeof(u32);
		addr |= *ireg++;
		ilen -= sizeof(u32);
		size = (unsigned long)*ireg++ << 32;
		ilen -= sizeof(u32);
		size |= *ireg++;
		ilen -= sizeof(u32);
		xics_map_one_cpu(*indx, addr, size);
		(*indx)++;
	}
}

void __init xics_init_IRQ(void)
{
	struct device_node *np;
	u32 indx = 0;
	int found = 0;

	ppc64_boot_msg(0x20, "XICS Init");

	ibm_get_xive = rtas_token("ibm,get-xive");
	ibm_set_xive = rtas_token("ibm,set-xive");
	ibm_int_on  = rtas_token("ibm,int-on");
	ibm_int_off = rtas_token("ibm,int-off");

	for_each_node_by_type(np, "PowerPC-External-Interrupt-Presentation") {
		found = 1;
		if (firmware_has_feature(FW_FEATURE_LPAR)) {
			of_node_put(np);
			break;
			}
		xics_init_one_node(np, &indx);
	}
	if (found == 0)
		return;

	xics_update_irq_servers();
	xics_init_host();

	if (firmware_has_feature(FW_FEATURE_LPAR))
		ppc_md.get_irq = xics_get_irq_lpar;
	else
		ppc_md.get_irq = xics_get_irq_direct;

	xics_setup_cpu();

	ppc64_boot_msg(0x21, "XICS Done");
}

/* Cpu startup, shutdown, and hotplug */

static void xics_set_cpu_priority(unsigned char cppr)
{
	if (firmware_has_feature(FW_FEATURE_LPAR))
		lpar_cppr_info(cppr);
	else
		direct_cppr_info(cppr);
	iosync();
}

/* Have the calling processor join or leave the specified global queue */
static void xics_set_cpu_giq(unsigned int gserver, unsigned int join)
{
	int status = rtas_set_indicator_fast(GLOBAL_INTERRUPT_QUEUE,
		(1UL << interrupt_server_size) - 1 - gserver, join);
	WARN_ON(status < 0);
}

void xics_setup_cpu(void)
{
	xics_set_cpu_priority(0xff);

	xics_set_cpu_giq(default_distrib_server, 1);
}

void xics_teardown_cpu(void)
{
	int cpu = smp_processor_id();

	xics_set_cpu_priority(0);

	/* Clear any pending IPI request */
	if (firmware_has_feature(FW_FEATURE_LPAR))
		lpar_qirr_info(cpu, 0xff);
	else
		direct_qirr_info(cpu, 0xff);
}

void xics_kexec_teardown_cpu(int secondary)
{
	xics_teardown_cpu();

	/*
	 * we take the ipi irq but and never return so we
	 * need to EOI the IPI, but want to leave our priority 0
	 *
	 * should we check all the other interrupts too?
	 * should we be flagging idle loop instead?
	 * or creating some task to be scheduled?
	 */

	if (firmware_has_feature(FW_FEATURE_LPAR))
		lpar_xirr_info_set((0x00 << 24) | XICS_IPI);
	else
		direct_xirr_info_set((0x00 << 24) | XICS_IPI);

	/*
	 * Some machines need to have at least one cpu in the GIQ,
	 * so leave the master cpu in the group.
	 */
	if (secondary)
		xics_set_cpu_giq(default_distrib_server, 0);
}

#ifdef CONFIG_HOTPLUG_CPU

/* Interrupts are disabled. */
void xics_migrate_irqs_away(void)
{
	int cpu = smp_processor_id(), hw_cpu = hard_smp_processor_id();
	unsigned int irq, virq;

	/* If we used to be the default server, move to the new "boot_cpuid" */
	if (hw_cpu == default_server)
		xics_update_irq_servers();

	/* Reject any interrupt that was queued to us... */
	xics_set_cpu_priority(0);

	/* Remove ourselves from the global interrupt queue */
	xics_set_cpu_giq(default_distrib_server, 0);

	/* Allow IPIs again... */
	xics_set_cpu_priority(DEFAULT_PRIORITY);

	for_each_irq(virq) {
		struct irq_desc *desc;
		int xics_status[2];
		int status;
		unsigned long flags;

		/* We cant set affinity on ISA interrupts */
		if (virq < NUM_ISA_INTERRUPTS)
			continue;
		if (irq_map[virq].host != xics_host)
			continue;
		irq = (unsigned int)irq_map[virq].hwirq;
		/* We need to get IPIs still. */
		if (irq == XICS_IPI || irq == XICS_IRQ_SPURIOUS)
			continue;
		desc = get_irq_desc(virq);

		/* We only need to migrate enabled IRQS */
		if (desc == NULL || desc->chip == NULL
		    || desc->action == NULL
		    || desc->chip->set_affinity == NULL)
			continue;

		spin_lock_irqsave(&desc->lock, flags);

		status = rtas_call(ibm_get_xive, 1, 3, xics_status, irq);
		if (status) {
			printk(KERN_ERR "%s: ibm,get-xive irq=%u returns %d\n",
					__func__, irq, status);
			goto unlock;
		}

		/*
		 * We only support delivery to all cpus or to one cpu.
		 * The irq has to be migrated only in the single cpu
		 * case.
		 */
		if (xics_status[0] != hw_cpu)
			goto unlock;

		printk(KERN_WARNING "IRQ %u affinity broken off cpu %u\n",
		       virq, cpu);

		/* Reset affinity to all cpus */
		irq_desc[virq].affinity = CPU_MASK_ALL;
		desc->chip->set_affinity(virq, CPU_MASK_ALL);
unlock:
		spin_unlock_irqrestore(&desc->lock, flags);
	}
}
#endif