diff options
Diffstat (limited to 'arch/x86/kernel/i8253.c')
| -rw-r--r-- | arch/x86/kernel/i8253.c | 208 |
1 files changed, 208 insertions, 0 deletions
diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c new file mode 100644 index 000000000000..5cc8841ca2c6 --- /dev/null +++ b/arch/x86/kernel/i8253.c @@ -0,0 +1,208 @@ +/* + * 8253/PIT functions + * + */ +#include <linux/clockchips.h> +#include <linux/init.h> +#include <linux/interrupt.h> +#include <linux/jiffies.h> +#include <linux/module.h> +#include <linux/spinlock.h> + +#include <asm/smp.h> +#include <asm/delay.h> +#include <asm/i8253.h> +#include <asm/io.h> + +DEFINE_SPINLOCK(i8253_lock); +EXPORT_SYMBOL(i8253_lock); + +/* + * HPET replaces the PIT, when enabled. So we need to know, which of + * the two timers is used + */ +struct clock_event_device *global_clock_event; + +/* + * Initialize the PIT timer. + * + * This is also called after resume to bring the PIT into operation again. + */ +static void init_pit_timer(enum clock_event_mode mode, + struct clock_event_device *evt) +{ + unsigned long flags; + + spin_lock_irqsave(&i8253_lock, flags); + + switch(mode) { + case CLOCK_EVT_MODE_PERIODIC: + /* binary, mode 2, LSB/MSB, ch 0 */ + outb_p(0x34, PIT_MODE); + outb_p(LATCH & 0xff , PIT_CH0); /* LSB */ + outb(LATCH >> 8 , PIT_CH0); /* MSB */ + break; + + case CLOCK_EVT_MODE_SHUTDOWN: + case CLOCK_EVT_MODE_UNUSED: + if (evt->mode == CLOCK_EVT_MODE_PERIODIC || + evt->mode == CLOCK_EVT_MODE_ONESHOT) { + outb_p(0x30, PIT_MODE); + outb_p(0, PIT_CH0); + outb_p(0, PIT_CH0); + } + break; + + case CLOCK_EVT_MODE_ONESHOT: + /* One shot setup */ + outb_p(0x38, PIT_MODE); + break; + + case CLOCK_EVT_MODE_RESUME: + /* Nothing to do here */ + break; + } + spin_unlock_irqrestore(&i8253_lock, flags); +} + +/* + * Program the next event in oneshot mode + * + * Delta is given in PIT ticks + */ +static int pit_next_event(unsigned long delta, struct clock_event_device *evt) +{ + unsigned long flags; + + spin_lock_irqsave(&i8253_lock, flags); + outb_p(delta & 0xff , PIT_CH0); /* LSB */ + outb(delta >> 8 , PIT_CH0); /* MSB */ + spin_unlock_irqrestore(&i8253_lock, flags); + + return 0; +} + +/* + * On UP the PIT can serve all of the possible timer functions. On SMP systems + * it can be solely used for the global tick. + * + * The profiling and update capabilites are switched off once the local apic is + * registered. This mechanism replaces the previous #ifdef LOCAL_APIC - + * !using_apic_timer decisions in do_timer_interrupt_hook() + */ +struct clock_event_device pit_clockevent = { + .name = "pit", + .features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT, + .set_mode = init_pit_timer, + .set_next_event = pit_next_event, + .shift = 32, + .irq = 0, +}; + +/* + * Initialize the conversion factor and the min/max deltas of the clock event + * structure and register the clock event source with the framework. + */ +void __init setup_pit_timer(void) +{ + /* + * Start pit with the boot cpu mask and make it global after the + * IO_APIC has been initialized. + */ + pit_clockevent.cpumask = cpumask_of_cpu(smp_processor_id()); + pit_clockevent.mult = div_sc(CLOCK_TICK_RATE, NSEC_PER_SEC, 32); + pit_clockevent.max_delta_ns = + clockevent_delta2ns(0x7FFF, &pit_clockevent); + pit_clockevent.min_delta_ns = + clockevent_delta2ns(0xF, &pit_clockevent); + clockevents_register_device(&pit_clockevent); + global_clock_event = &pit_clockevent; +} + +#ifndef CONFIG_X86_64 +/* + * 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); +} +arch_initcall(init_pit_clocksource); + +#endif |