john stultz | 8d016ef | 2006-06-26 00:25:09 -0700 | [diff] [blame] | 1 | /* |
| 2 | * i8253.c 8253/PIT functions |
| 3 | * |
| 4 | */ |
john stultz | 5d0cf41 | 2006-06-26 00:25:12 -0700 | [diff] [blame] | 5 | #include <linux/clocksource.h> |
john stultz | 8d016ef | 2006-06-26 00:25:09 -0700 | [diff] [blame] | 6 | #include <linux/spinlock.h> |
| 7 | #include <linux/jiffies.h> |
| 8 | #include <linux/sysdev.h> |
| 9 | #include <linux/module.h> |
| 10 | #include <linux/init.h> |
| 11 | |
| 12 | #include <asm/smp.h> |
| 13 | #include <asm/delay.h> |
| 14 | #include <asm/i8253.h> |
| 15 | #include <asm/io.h> |
| 16 | |
| 17 | #include "io_ports.h" |
| 18 | |
| 19 | DEFINE_SPINLOCK(i8253_lock); |
| 20 | EXPORT_SYMBOL(i8253_lock); |
| 21 | |
| 22 | void setup_pit_timer(void) |
| 23 | { |
| 24 | unsigned long flags; |
| 25 | |
| 26 | spin_lock_irqsave(&i8253_lock, flags); |
| 27 | outb_p(0x34,PIT_MODE); /* binary, mode 2, LSB/MSB, ch 0 */ |
| 28 | udelay(10); |
| 29 | outb_p(LATCH & 0xff , PIT_CH0); /* LSB */ |
| 30 | udelay(10); |
| 31 | outb(LATCH >> 8 , PIT_CH0); /* MSB */ |
| 32 | spin_unlock_irqrestore(&i8253_lock, flags); |
| 33 | } |
john stultz | 5d0cf41 | 2006-06-26 00:25:12 -0700 | [diff] [blame] | 34 | |
| 35 | /* |
| 36 | * Since the PIT overflows every tick, its not very useful |
| 37 | * to just read by itself. So use jiffies to emulate a free |
| 38 | * running counter: |
| 39 | */ |
| 40 | static cycle_t pit_read(void) |
| 41 | { |
| 42 | unsigned long flags; |
| 43 | int count; |
john stultz | 6415ce9 | 2006-06-26 00:25:16 -0700 | [diff] [blame] | 44 | u32 jifs; |
| 45 | static int old_count; |
| 46 | static u32 old_jifs; |
john stultz | 5d0cf41 | 2006-06-26 00:25:12 -0700 | [diff] [blame] | 47 | |
| 48 | spin_lock_irqsave(&i8253_lock, flags); |
john stultz | 6415ce9 | 2006-06-26 00:25:16 -0700 | [diff] [blame] | 49 | /* |
| 50 | * Although our caller may have the read side of xtime_lock, |
| 51 | * this is now a seqlock, and we are cheating in this routine |
| 52 | * by having side effects on state that we cannot undo if |
| 53 | * there is a collision on the seqlock and our caller has to |
| 54 | * retry. (Namely, old_jifs and old_count.) So we must treat |
| 55 | * jiffies as volatile despite the lock. We read jiffies |
| 56 | * before latching the timer count to guarantee that although |
| 57 | * the jiffies value might be older than the count (that is, |
| 58 | * the counter may underflow between the last point where |
| 59 | * jiffies was incremented and the point where we latch the |
| 60 | * count), it cannot be newer. |
| 61 | */ |
| 62 | jifs = jiffies; |
john stultz | 5d0cf41 | 2006-06-26 00:25:12 -0700 | [diff] [blame] | 63 | outb_p(0x00, PIT_MODE); /* latch the count ASAP */ |
| 64 | count = inb_p(PIT_CH0); /* read the latched count */ |
| 65 | count |= inb_p(PIT_CH0) << 8; |
| 66 | |
| 67 | /* VIA686a test code... reset the latch if count > max + 1 */ |
| 68 | if (count > LATCH) { |
| 69 | outb_p(0x34, PIT_MODE); |
| 70 | outb_p(LATCH & 0xff, PIT_CH0); |
| 71 | outb(LATCH >> 8, PIT_CH0); |
| 72 | count = LATCH - 1; |
| 73 | } |
john stultz | 6415ce9 | 2006-06-26 00:25:16 -0700 | [diff] [blame] | 74 | |
| 75 | /* |
| 76 | * It's possible for count to appear to go the wrong way for a |
| 77 | * couple of reasons: |
| 78 | * |
| 79 | * 1. The timer counter underflows, but we haven't handled the |
| 80 | * resulting interrupt and incremented jiffies yet. |
| 81 | * 2. Hardware problem with the timer, not giving us continuous time, |
| 82 | * the counter does small "jumps" upwards on some Pentium systems, |
| 83 | * (see c't 95/10 page 335 for Neptun bug.) |
| 84 | * |
| 85 | * Previous attempts to handle these cases intelligently were |
| 86 | * buggy, so we just do the simple thing now. |
| 87 | */ |
| 88 | if (count > old_count && jifs == old_jifs) { |
| 89 | count = old_count; |
| 90 | } |
| 91 | old_count = count; |
| 92 | old_jifs = jifs; |
| 93 | |
john stultz | 5d0cf41 | 2006-06-26 00:25:12 -0700 | [diff] [blame] | 94 | spin_unlock_irqrestore(&i8253_lock, flags); |
| 95 | |
john stultz | 6415ce9 | 2006-06-26 00:25:16 -0700 | [diff] [blame] | 96 | count = (LATCH - 1) - count; |
john stultz | 5d0cf41 | 2006-06-26 00:25:12 -0700 | [diff] [blame] | 97 | |
| 98 | return (cycle_t)(jifs * LATCH) + count; |
| 99 | } |
| 100 | |
| 101 | static struct clocksource clocksource_pit = { |
| 102 | .name = "pit", |
| 103 | .rating = 110, |
| 104 | .read = pit_read, |
john stultz | 6415ce9 | 2006-06-26 00:25:16 -0700 | [diff] [blame] | 105 | .mask = CLOCKSOURCE_MASK(32), |
john stultz | 5d0cf41 | 2006-06-26 00:25:12 -0700 | [diff] [blame] | 106 | .mult = 0, |
| 107 | .shift = 20, |
| 108 | }; |
| 109 | |
| 110 | static int __init init_pit_clocksource(void) |
| 111 | { |
| 112 | if (num_possible_cpus() > 4) /* PIT does not scale! */ |
| 113 | return 0; |
| 114 | |
| 115 | clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20); |
john stultz | a275254 | 2006-06-26 00:25:14 -0700 | [diff] [blame] | 116 | return clocksource_register(&clocksource_pit); |
john stultz | 5d0cf41 | 2006-06-26 00:25:12 -0700 | [diff] [blame] | 117 | } |
| 118 | module_init(init_pit_clocksource); |