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,
+};