[TG3]: Set minimal hw interrupt mitigation.
[linux-2.6/verdex.git] / arch / i386 / kernel / timers / timer_hpet.c
blobf778f471a09ab4934063225b4df1c7e7e8163c5e
1 /*
2 * This code largely moved from arch/i386/kernel/time.c.
3 * See comments there for proper credits.
4 */
6 #include <linux/spinlock.h>
7 #include <linux/init.h>
8 #include <linux/timex.h>
9 #include <linux/errno.h>
10 #include <linux/string.h>
11 #include <linux/jiffies.h>
13 #include <asm/timer.h>
14 #include <asm/io.h>
15 #include <asm/processor.h>
17 #include "io_ports.h"
18 #include "mach_timer.h"
19 #include <asm/hpet.h>
21 static unsigned long hpet_usec_quotient; /* convert hpet clks to usec */
22 static unsigned long tsc_hpet_quotient; /* convert tsc to hpet clks */
23 static unsigned long hpet_last; /* hpet counter value at last tick*/
24 static unsigned long last_tsc_low; /* lsb 32 bits of Time Stamp Counter */
25 static unsigned long last_tsc_high; /* msb 32 bits of Time Stamp Counter */
26 static unsigned long long monotonic_base;
27 static seqlock_t monotonic_lock = SEQLOCK_UNLOCKED;
29 /* convert from cycles(64bits) => nanoseconds (64bits)
30 * basic equation:
31 * ns = cycles / (freq / ns_per_sec)
32 * ns = cycles * (ns_per_sec / freq)
33 * ns = cycles * (10^9 / (cpu_mhz * 10^6))
34 * ns = cycles * (10^3 / cpu_mhz)
36 * Then we use scaling math (suggested by george@mvista.com) to get:
37 * ns = cycles * (10^3 * SC / cpu_mhz) / SC
38 * ns = cycles * cyc2ns_scale / SC
40 * And since SC is a constant power of two, we can convert the div
41 * into a shift.
42 * -johnstul@us.ibm.com "math is hard, lets go shopping!"
44 static unsigned long cyc2ns_scale;
45 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
47 static inline void set_cyc2ns_scale(unsigned long cpu_mhz)
49 cyc2ns_scale = (1000 << CYC2NS_SCALE_FACTOR)/cpu_mhz;
52 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
54 return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
57 static unsigned long long monotonic_clock_hpet(void)
59 unsigned long long last_offset, this_offset, base;
60 unsigned seq;
62 /* atomically read monotonic base & last_offset */
63 do {
64 seq = read_seqbegin(&monotonic_lock);
65 last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
66 base = monotonic_base;
67 } while (read_seqretry(&monotonic_lock, seq));
69 /* Read the Time Stamp Counter */
70 rdtscll(this_offset);
72 /* return the value in ns */
73 return base + cycles_2_ns(this_offset - last_offset);
76 static unsigned long get_offset_hpet(void)
78 register unsigned long eax, edx;
80 eax = hpet_readl(HPET_COUNTER);
81 eax -= hpet_last; /* hpet delta */
82 eax = min(hpet_tick, eax);
84 * Time offset = (hpet delta) * ( usecs per HPET clock )
85 * = (hpet delta) * ( usecs per tick / HPET clocks per tick)
86 * = (hpet delta) * ( hpet_usec_quotient ) / (2^32)
88 * Where,
89 * hpet_usec_quotient = (2^32 * usecs per tick)/HPET clocks per tick
91 * Using a mull instead of a divl saves some cycles in critical path.
93 ASM_MUL64_REG(eax, edx, hpet_usec_quotient, eax);
95 /* our adjusted time offset in microseconds */
96 return edx;
99 static void mark_offset_hpet(void)
101 unsigned long long this_offset, last_offset;
102 unsigned long offset;
104 write_seqlock(&monotonic_lock);
105 last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
106 rdtsc(last_tsc_low, last_tsc_high);
108 if (hpet_use_timer)
109 offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
110 else
111 offset = hpet_readl(HPET_COUNTER);
112 if (unlikely(((offset - hpet_last) >= (2*hpet_tick)) && (hpet_last != 0))) {
113 int lost_ticks = ((offset - hpet_last) / hpet_tick) - 1;
114 jiffies_64 += lost_ticks;
116 hpet_last = offset;
118 /* update the monotonic base value */
119 this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
120 monotonic_base += cycles_2_ns(this_offset - last_offset);
121 write_sequnlock(&monotonic_lock);
124 static void delay_hpet(unsigned long loops)
126 unsigned long hpet_start, hpet_end;
127 unsigned long eax;
129 /* loops is the number of cpu cycles. Convert it to hpet clocks */
130 ASM_MUL64_REG(eax, loops, tsc_hpet_quotient, loops);
132 hpet_start = hpet_readl(HPET_COUNTER);
133 do {
134 rep_nop();
135 hpet_end = hpet_readl(HPET_COUNTER);
136 } while ((hpet_end - hpet_start) < (loops));
139 static int __init init_hpet(char* override)
141 unsigned long result, remain;
143 /* check clock override */
144 if (override[0] && strncmp(override,"hpet",4))
145 return -ENODEV;
147 if (!is_hpet_enabled())
148 return -ENODEV;
150 printk("Using HPET for gettimeofday\n");
151 if (cpu_has_tsc) {
152 unsigned long tsc_quotient = calibrate_tsc_hpet(&tsc_hpet_quotient);
153 if (tsc_quotient) {
154 /* report CPU clock rate in Hz.
155 * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
156 * clock/second. Our precision is about 100 ppm.
158 { unsigned long eax=0, edx=1000;
159 ASM_DIV64_REG(cpu_khz, edx, tsc_quotient,
160 eax, edx);
161 printk("Detected %lu.%03lu MHz processor.\n",
162 cpu_khz / 1000, cpu_khz % 1000);
164 set_cyc2ns_scale(cpu_khz/1000);
169 * Math to calculate hpet to usec multiplier
170 * Look for the comments at get_offset_hpet()
172 ASM_DIV64_REG(result, remain, hpet_tick, 0, KERNEL_TICK_USEC);
173 if (remain > (hpet_tick >> 1))
174 result++; /* rounding the result */
175 hpet_usec_quotient = result;
177 return 0;
180 /************************************************************/
182 /* tsc timer_opts struct */
183 static struct timer_opts timer_hpet = {
184 .name = "hpet",
185 .mark_offset = mark_offset_hpet,
186 .get_offset = get_offset_hpet,
187 .monotonic_clock = monotonic_clock_hpet,
188 .delay = delay_hpet,
191 struct init_timer_opts __initdata timer_hpet_init = {
192 .init = init_hpet,
193 .opts = &timer_hpet,