summaryrefslogtreecommitdiffstats
path: root/drivers/clocksource/i8253.c
blob: 9c38895542f4abb5bff8c487ff22701e008443a2 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
// SPDX-License-Identifier: GPL-2.0
/*
 * i8253 PIT clocksource
 */
#include <linux/clockchips.h>
#include <linux/init.h>
#include <linux/io.h>
#include <linux/spinlock.h>
#include <linux/timex.h>
#include <linux/module.h>
#include <linux/i8253.h>
#include <linux/smp.h>

/*
 * Protects access to I/O ports
 *
 * 0040-0043 : timer0, i8253 / i8254
 * 0061-0061 : NMI Control Register which contains two speaker control bits.
 */
DEFINE_RAW_SPINLOCK(i8253_lock);
EXPORT_SYMBOL(i8253_lock);

#ifdef CONFIG_CLKSRC_I8253
/*
 * 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 u64 i8253_read(struct clocksource *cs)
{
	static int old_count;
	static u32 old_jifs;
	unsigned long flags;
	int count;
	u32 jifs;

	raw_spin_lock_irqsave(&i8253_lock, flags);
	/*
	 * Although our caller may have the read side of jiffies_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 > PIT_LATCH) {
		outb_p(0x34, PIT_MODE);
		outb_p(PIT_LATCH & 0xff, PIT_CH0);
		outb_p(PIT_LATCH >> 8, PIT_CH0);
		count = PIT_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;

	raw_spin_unlock_irqrestore(&i8253_lock, flags);

	count = (PIT_LATCH - 1) - count;

	return (u64)(jifs * PIT_LATCH) + count;
}

static struct clocksource i8253_cs = {
	.name		= "pit",
	.rating		= 110,
	.read		= i8253_read,
	.mask		= CLOCKSOURCE_MASK(32),
};

int __init clocksource_i8253_init(void)
{
	return clocksource_register_hz(&i8253_cs, PIT_TICK_RATE);
}
#endif

#ifdef CONFIG_CLKEVT_I8253
static int pit_shutdown(struct clock_event_device *evt)
{
	if (!clockevent_state_oneshot(evt) && !clockevent_state_periodic(evt))
		return 0;

	raw_spin_lock(&i8253_lock);

	outb_p(0x30, PIT_MODE);
	outb_p(0, PIT_CH0);
	outb_p(0, PIT_CH0);

	raw_spin_unlock(&i8253_lock);
	return 0;
}

static int pit_set_oneshot(struct clock_event_device *evt)
{
	raw_spin_lock(&i8253_lock);
	outb_p(0x38, PIT_MODE);
	raw_spin_unlock(&i8253_lock);
	return 0;
}

static int pit_set_periodic(struct clock_event_device *evt)
{
	raw_spin_lock(&i8253_lock);

	/* binary, mode 2, LSB/MSB, ch 0 */
	outb_p(0x34, PIT_MODE);
	outb_p(PIT_LATCH & 0xff, PIT_CH0);	/* LSB */
	outb_p(PIT_LATCH >> 8, PIT_CH0);	/* MSB */

	raw_spin_unlock(&i8253_lock);
	return 0;
}

/*
 * 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)
{
	raw_spin_lock(&i8253_lock);
	outb_p(delta & 0xff , PIT_CH0);	/* LSB */
	outb_p(delta >> 8 , PIT_CH0);		/* MSB */
	raw_spin_unlock(&i8253_lock);

	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.
 */
struct clock_event_device i8253_clockevent = {
	.name			= "pit",
	.features		= CLOCK_EVT_FEAT_PERIODIC,
	.set_state_shutdown	= pit_shutdown,
	.set_state_periodic	= pit_set_periodic,
	.set_next_event		= pit_next_event,
};

/*
 * 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 clockevent_i8253_init(bool oneshot)
{
	if (oneshot) {
		i8253_clockevent.features |= CLOCK_EVT_FEAT_ONESHOT;
		i8253_clockevent.set_state_oneshot = pit_set_oneshot;
	}
	/*
	 * Start pit with the boot cpu mask. x86 might make it global
	 * when it is used as broadcast device later.
	 */
	i8253_clockevent.cpumask = cpumask_of(smp_processor_id());

	clockevents_config_and_register(&i8253_clockevent, PIT_TICK_RATE,
					0xF, 0x7FFF);
}
#endif