| /* |
| * i8253.c 8253/PIT functions |
| * |
| */ |
| #include <linux/clocksource.h> |
| #include <linux/spinlock.h> |
| #include <linux/jiffies.h> |
| #include <linux/sysdev.h> |
| #include <linux/module.h> |
| #include <linux/init.h> |
| |
| #include <asm/smp.h> |
| #include <asm/delay.h> |
| #include <asm/i8253.h> |
| #include <asm/io.h> |
| |
| #include "io_ports.h" |
| |
| DEFINE_SPINLOCK(i8253_lock); |
| EXPORT_SYMBOL(i8253_lock); |
| |
| void setup_pit_timer(void) |
| { |
| unsigned long flags; |
| |
| spin_lock_irqsave(&i8253_lock, flags); |
| outb_p(0x34,PIT_MODE); /* binary, mode 2, LSB/MSB, ch 0 */ |
| udelay(10); |
| outb_p(LATCH & 0xff , PIT_CH0); /* LSB */ |
| udelay(10); |
| outb(LATCH >> 8 , PIT_CH0); /* MSB */ |
| spin_unlock_irqrestore(&i8253_lock, flags); |
| } |
| |
| /* |
| * Since the PIT overflows every tick, its not very useful |
| * to just read by itself. So use jiffies to emulate a free |
| * running counter: |
| */ |
| static cycle_t pit_read(void) |
| { |
| unsigned long flags; |
| int count; |
| u32 jifs; |
| static int old_count; |
| static u32 old_jifs; |
| |
| spin_lock_irqsave(&i8253_lock, flags); |
| /* |
| * Although our caller may have the read side of xtime_lock, |
| * this is now a seqlock, and we are cheating in this routine |
| * by having side effects on state that we cannot undo if |
| * there is a collision on the seqlock and our caller has to |
| * retry. (Namely, old_jifs and old_count.) So we must treat |
| * jiffies as volatile despite the lock. We read jiffies |
| * before latching the timer count to guarantee that although |
| * the jiffies value might be older than the count (that is, |
| * the counter may underflow between the last point where |
| * jiffies was incremented and the point where we latch the |
| * count), it cannot be newer. |
| */ |
| jifs = jiffies; |
| outb_p(0x00, PIT_MODE); /* latch the count ASAP */ |
| count = inb_p(PIT_CH0); /* read the latched count */ |
| count |= inb_p(PIT_CH0) << 8; |
| |
| /* VIA686a test code... reset the latch if count > max + 1 */ |
| if (count > LATCH) { |
| outb_p(0x34, PIT_MODE); |
| outb_p(LATCH & 0xff, PIT_CH0); |
| outb(LATCH >> 8, PIT_CH0); |
| count = LATCH - 1; |
| } |
| |
| /* |
| * It's possible for count to appear to go the wrong way for a |
| * couple of reasons: |
| * |
| * 1. The timer counter underflows, but we haven't handled the |
| * resulting interrupt and incremented jiffies yet. |
| * 2. Hardware problem with the timer, not giving us continuous time, |
| * the counter does small "jumps" upwards on some Pentium systems, |
| * (see c't 95/10 page 335 for Neptun bug.) |
| * |
| * Previous attempts to handle these cases intelligently were |
| * buggy, so we just do the simple thing now. |
| */ |
| if (count > old_count && jifs == old_jifs) { |
| count = old_count; |
| } |
| old_count = count; |
| old_jifs = jifs; |
| |
| spin_unlock_irqrestore(&i8253_lock, flags); |
| |
| count = (LATCH - 1) - count; |
| |
| return (cycle_t)(jifs * LATCH) + count; |
| } |
| |
| static struct clocksource clocksource_pit = { |
| .name = "pit", |
| .rating = 110, |
| .read = pit_read, |
| .mask = CLOCKSOURCE_MASK(32), |
| .mult = 0, |
| .shift = 20, |
| }; |
| |
| static int __init init_pit_clocksource(void) |
| { |
| if (num_possible_cpus() > 1) /* PIT does not scale! */ |
| return 0; |
| |
| clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20); |
| return clocksource_register(&clocksource_pit); |
| } |
| module_init(init_pit_clocksource); |