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196 lines
5.1 KiB
196 lines
5.1 KiB
// SPDX-License-Identifier: GPL-2.0 |
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/* |
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* i8253 PIT clocksource |
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*/ |
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#include <linux/clockchips.h> |
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#include <linux/init.h> |
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#include <linux/io.h> |
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#include <linux/spinlock.h> |
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#include <linux/timex.h> |
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#include <linux/module.h> |
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#include <linux/i8253.h> |
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#include <linux/smp.h> |
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/* |
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* Protects access to I/O ports |
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* |
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* 0040-0043 : timer0, i8253 / i8254 |
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* 0061-0061 : NMI Control Register which contains two speaker control bits. |
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*/ |
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DEFINE_RAW_SPINLOCK(i8253_lock); |
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EXPORT_SYMBOL(i8253_lock); |
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/* |
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* Handle PIT quirk in pit_shutdown() where zeroing the counter register |
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* restarts the PIT, negating the shutdown. On platforms with the quirk, |
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* platform specific code can set this to false. |
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*/ |
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bool i8253_clear_counter_on_shutdown __ro_after_init = true; |
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#ifdef CONFIG_CLKSRC_I8253 |
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/* |
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* Since the PIT overflows every tick, its not very useful |
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* to just read by itself. So use jiffies to emulate a free |
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* running counter: |
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*/ |
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static u64 i8253_read(struct clocksource *cs) |
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{ |
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static int old_count; |
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static u32 old_jifs; |
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unsigned long flags; |
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int count; |
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u32 jifs; |
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raw_spin_lock_irqsave(&i8253_lock, flags); |
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/* |
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* Although our caller may have the read side of jiffies_lock, |
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* this is now a seqlock, and we are cheating in this routine |
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* by having side effects on state that we cannot undo if |
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* there is a collision on the seqlock and our caller has to |
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* retry. (Namely, old_jifs and old_count.) So we must treat |
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* jiffies as volatile despite the lock. We read jiffies |
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* before latching the timer count to guarantee that although |
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* the jiffies value might be older than the count (that is, |
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* the counter may underflow between the last point where |
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* jiffies was incremented and the point where we latch the |
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* count), it cannot be newer. |
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*/ |
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jifs = jiffies; |
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outb_p(0x00, PIT_MODE); /* latch the count ASAP */ |
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count = inb_p(PIT_CH0); /* read the latched count */ |
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count |= inb_p(PIT_CH0) << 8; |
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/* VIA686a test code... reset the latch if count > max + 1 */ |
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if (count > PIT_LATCH) { |
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outb_p(0x34, PIT_MODE); |
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outb_p(PIT_LATCH & 0xff, PIT_CH0); |
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outb_p(PIT_LATCH >> 8, PIT_CH0); |
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count = PIT_LATCH - 1; |
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} |
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/* |
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* It's possible for count to appear to go the wrong way for a |
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* couple of reasons: |
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* |
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* 1. The timer counter underflows, but we haven't handled the |
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* resulting interrupt and incremented jiffies yet. |
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* 2. Hardware problem with the timer, not giving us continuous time, |
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* the counter does small "jumps" upwards on some Pentium systems, |
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* (see c't 95/10 page 335 for Neptun bug.) |
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* |
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* Previous attempts to handle these cases intelligently were |
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* buggy, so we just do the simple thing now. |
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*/ |
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if (count > old_count && jifs == old_jifs) |
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count = old_count; |
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old_count = count; |
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old_jifs = jifs; |
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raw_spin_unlock_irqrestore(&i8253_lock, flags); |
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count = (PIT_LATCH - 1) - count; |
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return (u64)(jifs * PIT_LATCH) + count; |
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} |
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static struct clocksource i8253_cs = { |
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.name = "pit", |
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.rating = 110, |
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.read = i8253_read, |
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.mask = CLOCKSOURCE_MASK(32), |
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}; |
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int __init clocksource_i8253_init(void) |
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{ |
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return clocksource_register_hz(&i8253_cs, PIT_TICK_RATE); |
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} |
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#endif |
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#ifdef CONFIG_CLKEVT_I8253 |
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static int pit_shutdown(struct clock_event_device *evt) |
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{ |
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if (!clockevent_state_oneshot(evt) && !clockevent_state_periodic(evt)) |
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return 0; |
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raw_spin_lock(&i8253_lock); |
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outb_p(0x30, PIT_MODE); |
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if (i8253_clear_counter_on_shutdown) { |
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outb_p(0, PIT_CH0); |
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outb_p(0, PIT_CH0); |
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} |
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raw_spin_unlock(&i8253_lock); |
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return 0; |
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} |
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static int pit_set_oneshot(struct clock_event_device *evt) |
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{ |
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raw_spin_lock(&i8253_lock); |
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outb_p(0x38, PIT_MODE); |
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raw_spin_unlock(&i8253_lock); |
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return 0; |
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} |
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static int pit_set_periodic(struct clock_event_device *evt) |
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{ |
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raw_spin_lock(&i8253_lock); |
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/* binary, mode 2, LSB/MSB, ch 0 */ |
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outb_p(0x34, PIT_MODE); |
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outb_p(PIT_LATCH & 0xff, PIT_CH0); /* LSB */ |
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outb_p(PIT_LATCH >> 8, PIT_CH0); /* MSB */ |
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raw_spin_unlock(&i8253_lock); |
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return 0; |
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} |
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/* |
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* Program the next event in oneshot mode |
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* |
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* Delta is given in PIT ticks |
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*/ |
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static int pit_next_event(unsigned long delta, struct clock_event_device *evt) |
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{ |
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raw_spin_lock(&i8253_lock); |
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outb_p(delta & 0xff , PIT_CH0); /* LSB */ |
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outb_p(delta >> 8 , PIT_CH0); /* MSB */ |
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raw_spin_unlock(&i8253_lock); |
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return 0; |
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} |
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/* |
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* On UP the PIT can serve all of the possible timer functions. On SMP systems |
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* it can be solely used for the global tick. |
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*/ |
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struct clock_event_device i8253_clockevent = { |
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.name = "pit", |
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.features = CLOCK_EVT_FEAT_PERIODIC, |
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.set_state_shutdown = pit_shutdown, |
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.set_state_periodic = pit_set_periodic, |
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.set_next_event = pit_next_event, |
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}; |
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/* |
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* Initialize the conversion factor and the min/max deltas of the clock event |
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* structure and register the clock event source with the framework. |
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*/ |
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void __init clockevent_i8253_init(bool oneshot) |
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{ |
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if (oneshot) { |
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i8253_clockevent.features |= CLOCK_EVT_FEAT_ONESHOT; |
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i8253_clockevent.set_state_oneshot = pit_set_oneshot; |
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} |
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/* |
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* Start pit with the boot cpu mask. x86 might make it global |
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* when it is used as broadcast device later. |
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*/ |
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i8253_clockevent.cpumask = cpumask_of(smp_processor_id()); |
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clockevents_config_and_register(&i8253_clockevent, PIT_TICK_RATE, |
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0xF, 0x7FFF); |
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} |
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#endif
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