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Diffstat (limited to 'arch/i386/kernel/timers/timer_hpet.c')
-rw-r--r--arch/i386/kernel/timers/timer_hpet.c191
1 files changed, 191 insertions, 0 deletions
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 <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 */
+
+ /*
+ * 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,
+};