From 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 16 Apr 2005 15:20:36 -0700 Subject: Linux-2.6.12-rc2 Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip! --- arch/i386/kernel/timers/timer_hpet.c | 191 +++++++++++++++++++++++++++++++++++ 1 file changed, 191 insertions(+) create mode 100644 arch/i386/kernel/timers/timer_hpet.c (limited to 'arch/i386/kernel/timers/timer_hpet.c') diff --git a/arch/i386/kernel/timers/timer_hpet.c b/arch/i386/kernel/timers/timer_hpet.c new file mode 100644 index 00000000000..713134e7184 --- /dev/null +++ b/arch/i386/kernel/timers/timer_hpet.c @@ -0,0 +1,191 @@ +/* + * This code largely moved from arch/i386/kernel/time.c. + * See comments there for proper credits. + */ + +#include +#include +#include +#include +#include +#include + +#include +#include +#include + +#include "io_ports.h" +#include "mach_timer.h" +#include + +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 */ + + /* + * 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); + + offset = hpet_readl(HPET_T0_CMP) - hpet_tick; + if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))) { + int lost_ticks = (offset - hpet_last) / hpet_tick; + 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 %lu.%03lu 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, +}; + +struct init_timer_opts __initdata timer_hpet_init = { + .init = init_hpet, + .opts = &timer_hpet, +}; -- cgit v1.2.3