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 __read_mostly;  /* convert hpet clks to usec */
  22 static unsigned long tsc_hpet_quotient __read_mostly;   /* 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_khz * 10^3))
  34  *              ns = cycles * (10^6 / cpu_khz)
  35  *
  36  *      Then we use scaling math (suggested by george@mvista.com) to get:
  37  *              ns = cycles * (10^6 * SC / cpu_khz) / 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  *
  43  *  We can use khz divisor instead of mhz to keep a better percision, since
  44  *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
  45  *  (mathieu.desnoyers@polymtl.ca)
  46  *
  47  *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
  48  */
  49 static unsigned long cyc2ns_scale __read_mostly;
  50 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
  51
  52 static inline void set_cyc2ns_scale(unsigned long cpu_khz)
  53 {
  54         cyc2ns_scale = (1000000 << CYC2NS_SCALE_FACTOR)/cpu_khz;
  55 }
  56
  57 static inline unsigned long long cycles_2_ns(unsigned long long cyc)
  58 {
  59         return (cyc * cyc2ns_scale) >> CYC2NS_SCALE_FACTOR;
  60 }
  61
  62 static unsigned long long monotonic_clock_hpet(void)
  63 {
  64         unsigned long long last_offset, this_offset, base;
  65         unsigned seq;
  66
  67         /* atomically read monotonic base & last_offset */
  68         do {
  69                 seq = read_seqbegin(&monotonic_lock);
  70                 last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
  71                 base = monotonic_base;
  72         } while (read_seqretry(&monotonic_lock, seq));
  73
  74         /* Read the Time Stamp Counter */
  75         rdtscll(this_offset);
  76
  77         /* return the value in ns */
  78         return base + cycles_2_ns(this_offset - last_offset);
  79 }
  80
  81 static unsigned long get_offset_hpet(void)
  82 {
  83         register unsigned long eax, edx;
  84
  85         eax = hpet_readl(HPET_COUNTER);
  86         eax -= hpet_last;       /* hpet delta */
  87         eax = min(hpet_tick, eax);
  88         /*
  89          * Time offset = (hpet delta) * ( usecs per HPET clock )
  90          *             = (hpet delta) * ( usecs per tick / HPET clocks per tick)
  91          *             = (hpet delta) * ( hpet_usec_quotient ) / (2^32)
  92          *
  93          * Where,
  94          * hpet_usec_quotient = (2^32 * usecs per tick)/HPET clocks per tick
  95          *
  96          * Using a mull instead of a divl saves some cycles in critical path.
  97          */
  98         ASM_MUL64_REG(eax, edx, hpet_usec_quotient, eax);
  99
 100         /* our adjusted time offset in microseconds */
 101         return edx;
 102 }
 103
 104 static void mark_offset_hpet(void)
 105 {
 106         unsigned long long this_offset, last_offset;
 107         unsigned long offset;
 108
 109         write_seqlock(&monotonic_lock);
 110         last_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
 111         rdtsc(last_tsc_low, last_tsc_high);
 112
 113         if (hpet_use_timer)
 114                 offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
 115         else
 116                 offset = hpet_readl(HPET_COUNTER);
 117         if (unlikely(((offset - hpet_last) >= (2*hpet_tick)) && (hpet_last != 0))) {
 118                 int lost_ticks = ((offset - hpet_last) / hpet_tick) - 1;
 119                 jiffies_64 += lost_ticks;
 120         }
 121         hpet_last = offset;
 122
 123         /* update the monotonic base value */
 124         this_offset = ((unsigned long long)last_tsc_high<<32)|last_tsc_low;
 125         monotonic_base += cycles_2_ns(this_offset - last_offset);
 126         write_sequnlock(&monotonic_lock);
 127 }
 128
 129 static void delay_hpet(unsigned long loops)
 130 {
 131         unsigned long hpet_start, hpet_end;
 132         unsigned long eax;
 133
 134         /* loops is the number of cpu cycles. Convert it to hpet clocks */
 135         ASM_MUL64_REG(eax, loops, tsc_hpet_quotient, loops);
 136
 137         hpet_start = hpet_readl(HPET_COUNTER);
 138         do {
 139                 rep_nop();
 140                 hpet_end = hpet_readl(HPET_COUNTER);
 141         } while ((hpet_end - hpet_start) < (loops));
 142 }
 143
 144 static struct timer_opts timer_hpet;
 145
 146 static int __init init_hpet(char* override)
 147 {
 148         unsigned long result, remain;
 149
 150         /* check clock override */
 151         if (override[0] && strncmp(override,"hpet",4))
 152                 return -ENODEV;
 153
 154         if (!is_hpet_enabled())
 155                 return -ENODEV;
 156
 157         printk("Using HPET for gettimeofday\n");
 158         if (cpu_has_tsc) {
 159                 unsigned long tsc_quotient = calibrate_tsc_hpet(&tsc_hpet_quotient);
 160                 if (tsc_quotient) {
 161                         /* report CPU clock rate in Hz.
 162                          * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
 163                          * clock/second. Our precision is about 100 ppm.
 164                          */
 165                         {       unsigned long eax=0, edx=1000;
 166                                 ASM_DIV64_REG(cpu_khz, edx, tsc_quotient,
 167                                                 eax, edx);
 168                                 printk("Detected %u.%03u MHz processor.\n",
 169                                         cpu_khz / 1000, cpu_khz % 1000);
 170                         }
 171                         set_cyc2ns_scale(cpu_khz);
 172                 }
 173                 /* set this only when cpu_has_tsc */
 174                 timer_hpet.read_timer = read_timer_tsc;
 175         }
 176
 177         /*
 178          * Math to calculate hpet to usec multiplier
 179          * Look for the comments at get_offset_hpet()
 180          */
 181         ASM_DIV64_REG(result, remain, hpet_tick, 0, KERNEL_TICK_USEC);
 182         if (remain > (hpet_tick >> 1))
 183                 result++; /* rounding the result */
 184         hpet_usec_quotient = result;
 185
 186         return 0;
 187 }
 188
 189 static int hpet_resume(void)
 190 {
 191         write_seqlock(&monotonic_lock);
 192         /* Assume this is the last mark offset time */
 193         rdtsc(last_tsc_low, last_tsc_high);
 194
 195         if (hpet_use_timer)
 196                 hpet_last = hpet_readl(HPET_T0_CMP) - hpet_tick;
 197         else
 198                 hpet_last = hpet_readl(HPET_COUNTER);
 199         write_sequnlock(&monotonic_lock);
 200         return 0;
 201 }
 202 /************************************************************/
 203
 204 /* tsc timer_opts struct */
 205 static struct timer_opts timer_hpet __read_mostly = {
 206         .name =                 "hpet",
 207         .mark_offset =          mark_offset_hpet,
 208         .get_offset =           get_offset_hpet,
 209         .monotonic_clock =      monotonic_clock_hpet,
 210         .delay =                delay_hpet,
 211         .resume =               hpet_resume,
 212 };
 213
 214 struct init_timer_opts __initdata timer_hpet_init = {
 215         .init = init_hpet,
 216         .opts = &timer_hpet,
 217 };