arch/i386/kernel/timers/timer_hpet.c

   1 /*
   2  * This code largely moved from arch/i386/kernel/time.c.
   3  * See comments there for proper credits.
   4  */
   5
   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>
  12
  13 #include <asm/timer.h>
  14 #include <asm/io.h>
  15 #include <asm/processor.h>
  16
  17 #include "io_ports.h"
  18 #include "mach_timer.h"
  19 #include <asm/hpet.h>
  20
  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;
  28
  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)
  35  *
  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
  39  *
  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!"
  43  */
  44 static unsigned long cyc2ns_scale;
  45 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
  46
  47 static inline void set_cyc2ns_scale(unsigned long cpu_mhz)
  48 {
  49         cyc2ns_scale = (1000 << CYC2NS_SCALE_FACTOR)/cpu_mhz;
  50 }
  51
  52 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
  53 {
  54         return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
  55 }
  56
  57 static unsigned long long monotonic_clock_hpet(void)
  58 {
  59         unsigned long long last_offset, this_offset, base;
  60         unsigned seq;
  61
  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));
  68
  69         /* Read the Time Stamp Counter */
  70         rdtscll(this_offset);
  71
  72         /* return the value in ns */
  73         return base + cycles_2_ns(this_offset - last_offset);
  74 }
  75
  76 static unsigned long get_offset_hpet(void)
  77 {
  78         register unsigned long eax, edx;
  79
  80         eax = hpet_readl(HPET_COUNTER);
  81         eax -= hpet_last;       /* hpet delta */
  82
  83         /*
  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)
  87          *
  88          * Where,
  89          * hpet_usec_quotient = (2^32 * usecs per tick)/HPET clocks per tick
  90          *
  91          * Using a mull instead of a divl saves some cycles in critical path.
  92          */
  93         ASM_MUL64_REG(eax, edx, hpet_usec_quotient, eax);
  94
  95         /* our adjusted time offset in microseconds */
  96         return edx;
  97 }
  98
  99 static void mark_offset_hpet(void)
 100 {
 101         unsigned long long this_offset, last_offset;
 102         unsigned long offset;
 103
 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);
 107
 108         offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
 109         if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))) {
 110                 int lost_ticks = (offset - hpet_last) / hpet_tick;
 111                 jiffies_64 += lost_ticks;
 112         }
 113         hpet_last = offset;
 114
 115         /* update the monotonic base value */
 116         this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
 117         monotonic_base += cycles_2_ns(this_offset - last_offset);
 118         write_sequnlock(&monotonic_lock);
 119 }
 120
 121 static void delay_hpet(unsigned long loops)
 122 {
 123         unsigned long hpet_start, hpet_end;
 124         unsigned long eax;
 125
 126         /* loops is the number of cpu cycles. Convert it to hpet clocks */
 127         ASM_MUL64_REG(eax, loops, tsc_hpet_quotient, loops);
 128
 129         hpet_start = hpet_readl(HPET_COUNTER);
 130         do {
 131                 rep_nop();
 132                 hpet_end = hpet_readl(HPET_COUNTER);
 133         } while ((hpet_end - hpet_start) < (loops));
 134 }
 135
 136 static int __init init_hpet(char* override)
 137 {
 138         unsigned long result, remain;
 139
 140         /* check clock override */
 141         if (override[0] && strncmp(override,"hpet",4))
 142                 return -ENODEV;
 143
 144         if (!is_hpet_enabled())
 145                 return -ENODEV;
 146
 147         printk("Using HPET for gettimeofday\n");
 148         if (cpu_has_tsc) {
 149                 unsigned long tsc_quotient = calibrate_tsc_hpet(&tsc_hpet_quotient);
 150                 if (tsc_quotient) {
 151                         /* report CPU clock rate in Hz.
 152                          * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
 153                          * clock/second. Our precision is about 100 ppm.
 154                          */
 155                         {       unsigned long eax=0, edx=1000;
 156                                 ASM_DIV64_REG(cpu_khz, edx, tsc_quotient,
 157                                                 eax, edx);
 158                                 printk("Detected %lu.%03lu MHz processor.\n",
 159                                         cpu_khz / 1000, cpu_khz % 1000);
 160                         }
 161                         set_cyc2ns_scale(cpu_khz/1000);
 162                 }
 163         }
 164
 165         /*
 166          * Math to calculate hpet to usec multiplier
 167          * Look for the comments at get_offset_hpet()
 168          */
 169         ASM_DIV64_REG(result, remain, hpet_tick, 0, KERNEL_TICK_USEC);
 170         if (remain > (hpet_tick >> 1))
 171                 result++; /* rounding the result */
 172         hpet_usec_quotient = result;
 173
 174         return 0;
 175 }
 176
 177 /************************************************************/
 178
 179 /* tsc timer_opts struct */
 180 static struct timer_opts timer_hpet = {
 181         .name =                 "hpet",
 182         .mark_offset =          mark_offset_hpet,
 183         .get_offset =           get_offset_hpet,
 184         .monotonic_clock =      monotonic_clock_hpet,
 185         .delay =                delay_hpet,
 186 };
 187
 188 struct init_timer_opts __initdata timer_hpet_init = {
 189         .init = init_hpet,
 190         .opts = &timer_hpet,
 191 };