aboutsummaryrefslogtreecommitdiff
path: root/arch/i386/kernel/timers/timer_hpet.c
blob: d766e0963ac13599db7707368ba833b331bcafeb (plain)
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
187
188
189
190
191
192
193
194
195
/*
 * This code largely moved from arch/i386/kernel/time.c.
 * See comments there for proper credits.
 */

#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/timex.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/jiffies.h>

#include <asm/timer.h>
#include <asm/io.h>
#include <asm/processor.h>

#include "io_ports.h"
#include "mach_timer.h"
#include <asm/hpet.h>

static unsigned long hpet_usec_quotient;	/* convert hpet clks to usec */
static unsigned long tsc_hpet_quotient;		/* convert tsc to hpet clks */
static unsigned long hpet_last; 	/* hpet counter value at last tick*/
static unsigned long last_tsc_low;	/* lsb 32 bits of Time Stamp Counter */
static unsigned long last_tsc_high; 	/* msb 32 bits of Time Stamp Counter */
static unsigned long long monotonic_base;
static seqlock_t monotonic_lock = SEQLOCK_UNLOCKED;

/* convert from cycles(64bits) => nanoseconds (64bits)
 *  basic equation:
 *		ns = cycles / (freq / ns_per_sec)
 *		ns = cycles * (ns_per_sec / freq)
 *		ns = cycles * (10^9 / (cpu_mhz * 10^6))
 *		ns = cycles * (10^3 / cpu_mhz)
 *
 *	Then we use scaling math (suggested by george@mvista.com) to get:
 *		ns = cycles * (10^3 * SC / cpu_mhz) / SC
 *		ns = cycles * cyc2ns_scale / SC
 *
 *	And since SC is a constant power of two, we can convert the div
 *  into a shift.
 *			-johnstul@us.ibm.com "math is hard, lets go shopping!"
 */
static unsigned long cyc2ns_scale;
#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */

static inline void set_cyc2ns_scale(unsigned long cpu_mhz)
{
	cyc2ns_scale = (1000 << CYC2NS_SCALE_FACTOR)/cpu_mhz;
}

static inline unsigned long long cycles_2_ns(unsigned long long cyc)
{
	return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
}

static unsigned long long monotonic_clock_hpet(void)
{
	unsigned long long last_offset, this_offset, base;
	unsigned seq;

	/* atomically read monotonic base & last_offset */
	do {
		seq = read_seqbegin(&monotonic_lock);
		last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
		base = monotonic_base;
	} while (read_seqretry(&monotonic_lock, seq));

	/* Read the Time Stamp Counter */
	rdtscll(this_offset);

	/* return the value in ns */
	return base + cycles_2_ns(this_offset - last_offset);
}

static unsigned long get_offset_hpet(void)
{
	register unsigned long eax, edx;

	eax = hpet_readl(HPET_COUNTER);
	eax -= hpet_last;	/* hpet delta */
	eax = min(hpet_tick, eax);
	/*
         * Time offset = (hpet delta) * ( usecs per HPET clock )
	 *             = (hpet delta) * ( usecs per tick / HPET clocks per tick)
	 *             = (hpet delta) * ( hpet_usec_quotient ) / (2^32)
	 *
	 * Where,
	 * hpet_usec_quotient = (2^32 * usecs per tick)/HPET clocks per tick
	 *
	 * Using a mull instead of a divl saves some cycles in critical path.
         */
	ASM_MUL64_REG(eax, edx, hpet_usec_quotient, eax);

	/* our adjusted time offset in microseconds */
	return edx;
}

static void mark_offset_hpet(void)
{
	unsigned long long this_offset, last_offset;
	unsigned long offset;

	write_seqlock(&monotonic_lock);
	last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
	rdtsc(last_tsc_low, last_tsc_high);

	if (hpet_use_timer)
		offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
	else
		offset = hpet_readl(HPET_COUNTER);
	if (unlikely(((offset - hpet_last) >= (2*hpet_tick)) && (hpet_last != 0))) {
		int lost_ticks = ((offset - hpet_last) / hpet_tick) - 1;
		jiffies_64 += lost_ticks;
	}
	hpet_last = offset;

	/* update the monotonic base value */
	this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
	monotonic_base += cycles_2_ns(this_offset - last_offset);
	write_sequnlock(&monotonic_lock);
}

static void delay_hpet(unsigned long loops)
{
	unsigned long hpet_start, hpet_end;
	unsigned long eax;

	/* loops is the number of cpu cycles. Convert it to hpet clocks */
	ASM_MUL64_REG(eax, loops, tsc_hpet_quotient, loops);

	hpet_start = hpet_readl(HPET_COUNTER);
	do {
		rep_nop();
		hpet_end = hpet_readl(HPET_COUNTER);
	} while ((hpet_end - hpet_start) < (loops));
}

static int __init init_hpet(char* override)
{
	unsigned long result, remain;

	/* check clock override */
	if (override[0] && strncmp(override,"hpet",4))
		return -ENODEV;

	if (!is_hpet_enabled())
		return -ENODEV;

	printk("Using HPET for gettimeofday\n");
	if (cpu_has_tsc) {
		unsigned long tsc_quotient = calibrate_tsc_hpet(&tsc_hpet_quotient);
		if (tsc_quotient) {
			/* report CPU clock rate in Hz.
			 * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
			 * clock/second. Our precision is about 100 ppm.
			 */
			{	unsigned long eax=0, edx=1000;
				ASM_DIV64_REG(cpu_khz, edx, tsc_quotient,
						eax, edx);
				printk("Detected %u.%03u MHz processor.\n",
					cpu_khz / 1000, cpu_khz % 1000);
			}
			set_cyc2ns_scale(cpu_khz/1000);
		}
	}

	/*
	 * Math to calculate hpet to usec multiplier
	 * Look for the comments at get_offset_hpet()
	 */
	ASM_DIV64_REG(result, remain, hpet_tick, 0, KERNEL_TICK_USEC);
	if (remain > (hpet_tick >> 1))
		result++; /* rounding the result */
	hpet_usec_quotient = result;

	return 0;
}

/************************************************************/

/* tsc timer_opts struct */
static struct timer_opts timer_hpet = {
	.name = 		"hpet",
	.mark_offset =		mark_offset_hpet,
	.get_offset =		get_offset_hpet,
	.monotonic_clock =	monotonic_clock_hpet,
	.delay = 		delay_hpet,
	.read_timer = 		read_timer_tsc,
};

struct init_timer_opts __initdata timer_hpet_init = {
	.init =	init_hpet,
	.opts = &timer_hpet,
};