1/* 2 * 8253/PIT functions 3 * 4 */ 5#include <linux/clockchips.h> 6#include <linux/interrupt.h> 7#include <linux/spinlock.h> 8#include <linux/jiffies.h> 9#include <linux/module.h> 10#include <linux/timex.h> 11#include <linux/delay.h> 12#include <linux/init.h> 13#include <linux/io.h> 14 15#include <asm/i8253.h> 16#include <asm/hpet.h> 17#include <asm/smp.h> 18 19DEFINE_RAW_SPINLOCK(i8253_lock); 20EXPORT_SYMBOL(i8253_lock); 21 22/* 23 * HPET replaces the PIT, when enabled. So we need to know, which of 24 * the two timers is used 25 */ 26struct clock_event_device *global_clock_event; 27 28/* 29 * Initialize the PIT timer. 30 * 31 * This is also called after resume to bring the PIT into operation again. 32 */ 33static void init_pit_timer(enum clock_event_mode mode, 34 struct clock_event_device *evt) 35{ 36 raw_spin_lock(&i8253_lock); 37 38 switch (mode) { 39 case CLOCK_EVT_MODE_PERIODIC: 40 /* binary, mode 2, LSB/MSB, ch 0 */ 41 outb_pit(0x34, PIT_MODE); 42 outb_pit(LATCH & 0xff , PIT_CH0); /* LSB */ 43 outb_pit(LATCH >> 8 , PIT_CH0); /* MSB */ 44 break; 45 46 case CLOCK_EVT_MODE_SHUTDOWN: 47 case CLOCK_EVT_MODE_UNUSED: 48 if (evt->mode == CLOCK_EVT_MODE_PERIODIC || 49 evt->mode == CLOCK_EVT_MODE_ONESHOT) { 50 outb_pit(0x30, PIT_MODE); 51 outb_pit(0, PIT_CH0); 52 outb_pit(0, PIT_CH0); 53 } 54 break; 55 56 case CLOCK_EVT_MODE_ONESHOT: 57 /* One shot setup */ 58 outb_pit(0x38, PIT_MODE); 59 break; 60 61 case CLOCK_EVT_MODE_RESUME: 62 /* Nothing to do here */ 63 break; 64 } 65 raw_spin_unlock(&i8253_lock); 66} 67 68/* 69 * Program the next event in oneshot mode 70 * 71 * Delta is given in PIT ticks 72 */ 73static int pit_next_event(unsigned long delta, struct clock_event_device *evt) 74{ 75 raw_spin_lock(&i8253_lock); 76 outb_pit(delta & 0xff , PIT_CH0); /* LSB */ 77 outb_pit(delta >> 8 , PIT_CH0); /* MSB */ 78 raw_spin_unlock(&i8253_lock); 79 80 return 0; 81} 82 83/* 84 * On UP the PIT can serve all of the possible timer functions. On SMP systems 85 * it can be solely used for the global tick. 86 * 87 * The profiling and update capabilities are switched off once the local apic is 88 * registered. This mechanism replaces the previous #ifdef LOCAL_APIC - 89 * !using_apic_timer decisions in do_timer_interrupt_hook() 90 */ 91static struct clock_event_device pit_ce = { 92 .name = "pit", 93 .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT, 94 .set_mode = init_pit_timer, 95 .set_next_event = pit_next_event, 96 .shift = 32, 97 .irq = 0, 98}; 99 100/* 101 * Initialize the conversion factor and the min/max deltas of the clock event 102 * structure and register the clock event source with the framework. 103 */ 104void __init setup_pit_timer(void) 105{ 106 /* 107 * Start pit with the boot cpu mask and make it global after the 108 * IO_APIC has been initialized. 109 */ 110 pit_ce.cpumask = cpumask_of(smp_processor_id()); 111 pit_ce.mult = div_sc(CLOCK_TICK_RATE, NSEC_PER_SEC, pit_ce.shift); 112 pit_ce.max_delta_ns = clockevent_delta2ns(0x7FFF, &pit_ce); 113 pit_ce.min_delta_ns = clockevent_delta2ns(0xF, &pit_ce); 114 115 clockevents_register_device(&pit_ce); 116 global_clock_event = &pit_ce; 117} 118 119#ifndef CONFIG_X86_64 120/* 121 * Since the PIT overflows every tick, its not very useful 122 * to just read by itself. So use jiffies to emulate a free 123 * running counter: 124 */ 125static cycle_t pit_read(struct clocksource *cs) 126{ 127 static int old_count; 128 static u32 old_jifs; 129 unsigned long flags; 130 int count; 131 u32 jifs; 132 133 raw_spin_lock_irqsave(&i8253_lock, flags); 134 /* 135 * Although our caller may have the read side of xtime_lock, 136 * this is now a seqlock, and we are cheating in this routine 137 * by having side effects on state that we cannot undo if 138 * there is a collision on the seqlock and our caller has to 139 * retry. (Namely, old_jifs and old_count.) So we must treat 140 * jiffies as volatile despite the lock. We read jiffies 141 * before latching the timer count to guarantee that although 142 * the jiffies value might be older than the count (that is, 143 * the counter may underflow between the last point where 144 * jiffies was incremented and the point where we latch the 145 * count), it cannot be newer. 146 */ 147 jifs = jiffies; 148 outb_pit(0x00, PIT_MODE); /* latch the count ASAP */ 149 count = inb_pit(PIT_CH0); /* read the latched count */ 150 count |= inb_pit(PIT_CH0) << 8; 151 152 /* VIA686a test code... reset the latch if count > max + 1 */ 153 if (count > LATCH) { 154 outb_pit(0x34, PIT_MODE); 155 outb_pit(LATCH & 0xff, PIT_CH0); 156 outb_pit(LATCH >> 8, PIT_CH0); 157 count = LATCH - 1; 158 } 159 160 /* 161 * It's possible for count to appear to go the wrong way for a 162 * couple of reasons: 163 * 164 * 1. The timer counter underflows, but we haven't handled the 165 * resulting interrupt and incremented jiffies yet. 166 * 2. Hardware problem with the timer, not giving us continuous time, 167 * the counter does small "jumps" upwards on some Pentium systems, 168 * (see c't 95/10 page 335 for Neptun bug.) 169 * 170 * Previous attempts to handle these cases intelligently were 171 * buggy, so we just do the simple thing now. 172 */ 173 if (count > old_count && jifs == old_jifs) 174 count = old_count; 175 176 old_count = count; 177 old_jifs = jifs; 178 179 raw_spin_unlock_irqrestore(&i8253_lock, flags); 180 181 count = (LATCH - 1) - count; 182 183 return (cycle_t)(jifs * LATCH) + count; 184} 185 186static struct clocksource pit_cs = { 187 .name = "pit", 188 .rating = 110, 189 .read = pit_read, 190 .mask = CLOCKSOURCE_MASK(32), 191 .mult = 0, 192 .shift = 20, 193}; 194 195static int __init init_pit_clocksource(void) 196{ 197 /* 198 * Several reasons not to register PIT as a clocksource: 199 * 200 * - On SMP PIT does not scale due to i8253_lock 201 * - when HPET is enabled 202 * - when local APIC timer is active (PIT is switched off) 203 */ 204 if (num_possible_cpus() > 1 || is_hpet_enabled() || 205 pit_ce.mode != CLOCK_EVT_MODE_PERIODIC) 206 return 0; 207 208 pit_cs.mult = clocksource_hz2mult(CLOCK_TICK_RATE, pit_cs.shift); 209 210 return clocksource_register(&pit_cs); 211} 212arch_initcall(init_pit_clocksource); 213 214#endif /* !CONFIG_X86_64 */ 215