Initial import

1 files changed, 1245 insertions, 0 deletions

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
new file mode 100644
index 000000000..f95603842
--- /dev/null
+++ b/arch/x86/kernel/tsc.c
@@ -0,0 +1,1245 @@
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/timer.h>
+#include <linux/acpi_pmtmr.h>
+#include <linux/cpufreq.h>
+#include <linux/delay.h>
+#include <linux/clocksource.h>
+#include <linux/percpu.h>
+#include <linux/timex.h>
+#include <linux/static_key.h>
+#include <linux/mm.h>
+
+#include <asm/hpet.h>
+#include <asm/timer.h>
+#include <asm/vgtod.h>
+#include <asm/time.h>
+#include <asm/delay.h>
+#include <asm/hypervisor.h>
+#include <asm/nmi.h>
+#include <asm/x86_init.h>
+
+unsigned int __read_mostly cpu_khz;	/* TSC clocks / usec, not used here */
+EXPORT_SYMBOL(cpu_khz);
+
+unsigned int __read_mostly tsc_khz;
+EXPORT_SYMBOL(tsc_khz);
+
+/*
+ * TSC can be unstable due to cpufreq or due to unsynced TSCs
+ */
+static int __read_mostly tsc_unstable;
+
+/* native_sched_clock() is called before tsc_init(), so
+   we must start with the TSC soft disabled to prevent
+   erroneous rdtsc usage on !cpu_has_tsc processors */
+static int __read_mostly tsc_disabled = -1;
+
+static struct static_key __use_tsc = STATIC_KEY_INIT;
+
+int tsc_clocksource_reliable;
+
+/*
+ * Use a ring-buffer like data structure, where a writer advances the head by
+ * writing a new data entry and a reader advances the tail when it observes a
+ * new entry.
+ *
+ * Writers are made to wait on readers until there's space to write a new
+ * entry.
+ *
+ * This means that we can always use an {offset, mul} pair to compute a ns
+ * value that is 'roughly' in the right direction, even if we're writing a new
+ * {offset, mul} pair during the clock read.
+ *
+ * The down-side is that we can no longer guarantee strict monotonicity anymore
+ * (assuming the TSC was that to begin with), because while we compute the
+ * intersection point of the two clock slopes and make sure the time is
+ * continuous at the point of switching; we can no longer guarantee a reader is
+ * strictly before or after the switch point.
+ *
+ * It does mean a reader no longer needs to disable IRQs in order to avoid
+ * CPU-Freq updates messing with his times, and similarly an NMI reader will
+ * no longer run the risk of hitting half-written state.
+ */
+
+struct cyc2ns {
+	struct cyc2ns_data data[2];	/*  0 + 2*24 = 48 */
+	struct cyc2ns_data *head;	/* 48 + 8    = 56 */
+	struct cyc2ns_data *tail;	/* 56 + 8    = 64 */
+}; /* exactly fits one cacheline */
+
+static DEFINE_PER_CPU_ALIGNED(struct cyc2ns, cyc2ns);
+
+struct cyc2ns_data *cyc2ns_read_begin(void)
+{
+	struct cyc2ns_data *head;
+
+	preempt_disable();
+
+	head = this_cpu_read(cyc2ns.head);
+	/*
+	 * Ensure we observe the entry when we observe the pointer to it.
+	 * matches the wmb from cyc2ns_write_end().
+	 */
+	smp_read_barrier_depends();
+	head->__count++;
+	barrier();
+
+	return head;
+}
+
+void cyc2ns_read_end(struct cyc2ns_data *head)
+{
+	barrier();
+	/*
+	 * If we're the outer most nested read; update the tail pointer
+	 * when we're done. This notifies possible pending writers
+	 * that we've observed the head pointer and that the other
+	 * entry is now free.
+	 */
+	if (!--head->__count) {
+		/*
+		 * x86-TSO does not reorder writes with older reads;
+		 * therefore once this write becomes visible to another
+		 * cpu, we must be finished reading the cyc2ns_data.
+		 *
+		 * matches with cyc2ns_write_begin().
+		 */
+		this_cpu_write(cyc2ns.tail, head);
+	}
+	preempt_enable();
+}
+
+/*
+ * Begin writing a new @data entry for @cpu.
+ *
+ * Assumes some sort of write side lock; currently 'provided' by the assumption
+ * that cpufreq will call its notifiers sequentially.
+ */
+static struct cyc2ns_data *cyc2ns_write_begin(int cpu)
+{
+	struct cyc2ns *c2n = &per_cpu(cyc2ns, cpu);
+	struct cyc2ns_data *data = c2n->data;
+
+	if (data == c2n->head)
+		data++;
+
+	/* XXX send an IPI to @cpu in order to guarantee a read? */
+
+	/*
+	 * When we observe the tail write from cyc2ns_read_end(),
+	 * the cpu must be done with that entry and its safe
+	 * to start writing to it.
+	 */
+	while (c2n->tail == data)
+		cpu_relax();
+
+	return data;
+}
+
+static void cyc2ns_write_end(int cpu, struct cyc2ns_data *data)
+{
+	struct cyc2ns *c2n = &per_cpu(cyc2ns, cpu);
+
+	/*
+	 * Ensure the @data writes are visible before we publish the
+	 * entry. Matches the data-depencency in cyc2ns_read_begin().
+	 */
+	smp_wmb();
+
+	ACCESS_ONCE(c2n->head) = data;
+}
+
+/*
+ * Accelerators for sched_clock()
+ * 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_khz * 10^3))
+ *              ns = cycles * (10^6 / cpu_khz)
+ *
+ *      Then we use scaling math (suggested by george@mvista.com) to get:
+ *              ns = cycles * (10^6 * SC / cpu_khz) / SC
+ *              ns = cycles * cyc2ns_scale / SC
+ *
+ *      And since SC is a constant power of two, we can convert the div
+ *  into a shift.
+ *
+ *  We can use khz divisor instead of mhz to keep a better precision, since
+ *  cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
+ *  (mathieu.desnoyers@polymtl.ca)
+ *
+ *                      -johnstul@us.ibm.com "math is hard, lets go shopping!"
+ */
+
+#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
+
+static void cyc2ns_data_init(struct cyc2ns_data *data)
+{
+	data->cyc2ns_mul = 0;
+	data->cyc2ns_shift = CYC2NS_SCALE_FACTOR;
+	data->cyc2ns_offset = 0;
+	data->__count = 0;
+}
+
+static void cyc2ns_init(int cpu)
+{
+	struct cyc2ns *c2n = &per_cpu(cyc2ns, cpu);
+
+	cyc2ns_data_init(&c2n->data[0]);
+	cyc2ns_data_init(&c2n->data[1]);
+
+	c2n->head = c2n->data;
+	c2n->tail = c2n->data;
+
+        // Don't let TuxOnIce make data RO - a secondary CPU will cause a triple fault
+        // if it loads microcode, which then does a printk, which may end up invoking cycles_2_ns
+        SetPageTOI_Untracked(virt_to_page(c2n));
+}
+
+static inline unsigned long long cycles_2_ns(unsigned long long cyc)
+{
+	struct cyc2ns_data *data, *tail;
+	unsigned long long ns;
+
+	/*
+	 * See cyc2ns_read_*() for details; replicated in order to avoid
+	 * an extra few instructions that came with the abstraction.
+	 * Notable, it allows us to only do the __count and tail update
+	 * dance when its actually needed.
+	 */
+
+	preempt_disable_notrace();
+	data = this_cpu_read(cyc2ns.head);
+	tail = this_cpu_read(cyc2ns.tail);
+
+	if (likely(data == tail)) {
+		ns = data->cyc2ns_offset;
+		ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
+	} else {
+		data->__count++;
+
+		barrier();
+
+		ns = data->cyc2ns_offset;
+		ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
+
+		barrier();
+
+		if (!--data->__count)
+			this_cpu_write(cyc2ns.tail, data);
+	}
+	preempt_enable_notrace();
+
+	return ns;
+}
+
+static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
+{
+	unsigned long long tsc_now, ns_now;
+	struct cyc2ns_data *data;
+	unsigned long flags;
+
+	local_irq_save(flags);
+	sched_clock_idle_sleep_event();
+
+	if (!cpu_khz)
+		goto done;
+
+	data = cyc2ns_write_begin(cpu);
+
+	rdtscll(tsc_now);
+	ns_now = cycles_2_ns(tsc_now);
+
+	/*
+	 * Compute a new multiplier as per the above comment and ensure our
+	 * time function is continuous; see the comment near struct
+	 * cyc2ns_data.
+	 */
+	data->cyc2ns_mul =
+		DIV_ROUND_CLOSEST(NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR,
+				  cpu_khz);
+	data->cyc2ns_shift = CYC2NS_SCALE_FACTOR;
+	data->cyc2ns_offset = ns_now -
+		mul_u64_u32_shr(tsc_now, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
+
+	cyc2ns_write_end(cpu, data);
+
+done:
+	sched_clock_idle_wakeup_event(0);
+	local_irq_restore(flags);
+}
+/*
+ * Scheduler clock - returns current time in nanosec units.
+ */
+u64 native_sched_clock(void)
+{
+	u64 tsc_now;
+
+	/*
+	 * Fall back to jiffies if there's no TSC available:
+	 * ( But note that we still use it if the TSC is marked
+	 *   unstable. We do this because unlike Time Of Day,
+	 *   the scheduler clock tolerates small errors and it's
+	 *   very important for it to be as fast as the platform
+	 *   can achieve it. )
+	 */
+	if (!static_key_false(&__use_tsc)) {
+		/* No locking but a rare wrong value is not a big deal: */
+		return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
+	}
+
+	/* read the Time Stamp Counter: */
+	rdtscll(tsc_now);
+
+	/* return the value in ns */
+	return cycles_2_ns(tsc_now);
+}
+
+/* We need to define a real function for sched_clock, to override the
+   weak default version */
+#ifdef CONFIG_PARAVIRT
+unsigned long long sched_clock(void)
+{
+	return paravirt_sched_clock();
+}
+#else
+unsigned long long
+sched_clock(void) __attribute__((alias("native_sched_clock")));
+#endif
+
+unsigned long long native_read_tsc(void)
+{
+	return __native_read_tsc();
+}
+EXPORT_SYMBOL(native_read_tsc);
+
+int check_tsc_unstable(void)
+{
+	return tsc_unstable;
+}
+EXPORT_SYMBOL_GPL(check_tsc_unstable);
+
+int check_tsc_disabled(void)
+{
+	return tsc_disabled;
+}
+EXPORT_SYMBOL_GPL(check_tsc_disabled);
+
+#ifdef CONFIG_X86_TSC
+int __init notsc_setup(char *str)
+{
+	pr_warn("Kernel compiled with CONFIG_X86_TSC, cannot disable TSC completely\n");
+	tsc_disabled = 1;
+	return 1;
+}
+#else
+/*
+ * disable flag for tsc. Takes effect by clearing the TSC cpu flag
+ * in cpu/common.c
+ */
+int __init notsc_setup(char *str)
+{
+	setup_clear_cpu_cap(X86_FEATURE_TSC);
+	return 1;
+}
+#endif
+
+__setup("notsc", notsc_setup);
+
+static int no_sched_irq_time;
+
+static int __init tsc_setup(char *str)
+{
+	if (!strcmp(str, "reliable"))
+		tsc_clocksource_reliable = 1;
+	if (!strncmp(str, "noirqtime", 9))
+		no_sched_irq_time = 1;
+	return 1;
+}
+
+__setup("tsc=", tsc_setup);
+
+#define MAX_RETRIES     5
+#define SMI_TRESHOLD    50000
+
+/*
+ * Read TSC and the reference counters. Take care of SMI disturbance
+ */
+static u64 tsc_read_refs(u64 *p, int hpet)
+{
+	u64 t1, t2;
+	int i;
+
+	for (i = 0; i < MAX_RETRIES; i++) {
+		t1 = get_cycles();
+		if (hpet)
+			*p = hpet_readl(HPET_COUNTER) & 0xFFFFFFFF;
+		else
+			*p = acpi_pm_read_early();
+		t2 = get_cycles();
+		if ((t2 - t1) < SMI_TRESHOLD)
+			return t2;
+	}
+	return ULLONG_MAX;
+}
+
+/*
+ * Calculate the TSC frequency from HPET reference
+ */
+static unsigned long calc_hpet_ref(u64 deltatsc, u64 hpet1, u64 hpet2)
+{
+	u64 tmp;
+
+	if (hpet2 < hpet1)
+		hpet2 += 0x100000000ULL;
+	hpet2 -= hpet1;
+	tmp = ((u64)hpet2 * hpet_readl(HPET_PERIOD));
+	do_div(tmp, 1000000);
+	do_div(deltatsc, tmp);
+
+	return (unsigned long) deltatsc;
+}
+
+/*
+ * Calculate the TSC frequency from PMTimer reference
+ */
+static unsigned long calc_pmtimer_ref(u64 deltatsc, u64 pm1, u64 pm2)
+{
+	u64 tmp;
+
+	if (!pm1 && !pm2)
+		return ULONG_MAX;
+
+	if (pm2 < pm1)
+		pm2 += (u64)ACPI_PM_OVRRUN;
+	pm2 -= pm1;
+	tmp = pm2 * 1000000000LL;
+	do_div(tmp, PMTMR_TICKS_PER_SEC);
+	do_div(deltatsc, tmp);
+
+	return (unsigned long) deltatsc;
+}
+
+#define CAL_MS		10
+#define CAL_LATCH	(PIT_TICK_RATE / (1000 / CAL_MS))
+#define CAL_PIT_LOOPS	1000
+
+#define CAL2_MS		50
+#define CAL2_LATCH	(PIT_TICK_RATE / (1000 / CAL2_MS))
+#define CAL2_PIT_LOOPS	5000
+
+
+/*
+ * Try to calibrate the TSC against the Programmable
+ * Interrupt Timer and return the frequency of the TSC
+ * in kHz.
+ *
+ * Return ULONG_MAX on failure to calibrate.
+ */
+static unsigned long pit_calibrate_tsc(u32 latch, unsigned long ms, int loopmin)
+{
+	u64 tsc, t1, t2, delta;
+	unsigned long tscmin, tscmax;
+	int pitcnt;
+
+	/* Set the Gate high, disable speaker */
+	outb((inb(0x61) & ~0x02) | 0x01, 0x61);
+
+	/*
+	 * Setup CTC channel 2* for mode 0, (interrupt on terminal
+	 * count mode), binary count. Set the latch register to 50ms
+	 * (LSB then MSB) to begin countdown.
+	 */
+	outb(0xb0, 0x43);
+	outb(latch & 0xff, 0x42);
+	outb(latch >> 8, 0x42);
+
+	tsc = t1 = t2 = get_cycles();
+
+	pitcnt = 0;
+	tscmax = 0;
+	tscmin = ULONG_MAX;
+	while ((inb(0x61) & 0x20) == 0) {
+		t2 = get_cycles();
+		delta = t2 - tsc;
+		tsc = t2;
+		if ((unsigned long) delta < tscmin)
+			tscmin = (unsigned int) delta;
+		if ((unsigned long) delta > tscmax)
+			tscmax = (unsigned int) delta;
+		pitcnt++;
+	}
+
+	/*
+	 * Sanity checks:
+	 *
+	 * If we were not able to read the PIT more than loopmin
+	 * times, then we have been hit by a massive SMI
+	 *
+	 * If the maximum is 10 times larger than the minimum,
+	 * then we got hit by an SMI as well.
+	 */
+	if (pitcnt < loopmin || tscmax > 10 * tscmin)
+		return ULONG_MAX;
+
+	/* Calculate the PIT value */
+	delta = t2 - t1;
+	do_div(delta, ms);
+	return delta;
+}
+
+/*
+ * This reads the current MSB of the PIT counter, and
+ * checks if we are running on sufficiently fast and
+ * non-virtualized hardware.
+ *
+ * Our expectations are:
+ *
+ *  - the PIT is running at roughly 1.19MHz
+ *
+ *  - each IO is going to take about 1us on real hardware,
+ *    but we allow it to be much faster (by a factor of 10) or
+ *    _slightly_ slower (ie we allow up to a 2us read+counter
+ *    update - anything else implies a unacceptably slow CPU
+ *    or PIT for the fast calibration to work.
+ *
+ *  - with 256 PIT ticks to read the value, we have 214us to
+ *    see the same MSB (and overhead like doing a single TSC
+ *    read per MSB value etc).
+ *
+ *  - We're doing 2 reads per loop (LSB, MSB), and we expect
+ *    them each to take about a microsecond on real hardware.
+ *    So we expect a count value of around 100. But we'll be
+ *    generous, and accept anything over 50.
+ *
+ *  - if the PIT is stuck, and we see *many* more reads, we
+ *    return early (and the next caller of pit_expect_msb()
+ *    then consider it a failure when they don't see the
+ *    next expected value).
+ *
+ * These expectations mean that we know that we have seen the
+ * transition from one expected value to another with a fairly
+ * high accuracy, and we didn't miss any events. We can thus
+ * use the TSC value at the transitions to calculate a pretty
+ * good value for the TSC frequencty.
+ */
+static inline int pit_verify_msb(unsigned char val)
+{
+	/* Ignore LSB */
+	inb(0x42);
+	return inb(0x42) == val;
+}
+
+static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *deltap)
+{
+	int count;
+	u64 tsc = 0, prev_tsc = 0;
+
+	for (count = 0; count < 50000; count++) {
+		if (!pit_verify_msb(val))
+			break;
+		prev_tsc = tsc;
+		tsc = get_cycles();
+	}
+	*deltap = get_cycles() - prev_tsc;
+	*tscp = tsc;
+
+	/*
+	 * We require _some_ success, but the quality control
+	 * will be based on the error terms on the TSC values.
+	 */
+	return count > 5;
+}
+
+/*
+ * How many MSB values do we want to see? We aim for
+ * a maximum error rate of 500ppm (in practice the
+ * real error is much smaller), but refuse to spend
+ * more than 50ms on it.
+ */
+#define MAX_QUICK_PIT_MS 50
+#define MAX_QUICK_PIT_ITERATIONS (MAX_QUICK_PIT_MS * PIT_TICK_RATE / 1000 / 256)
+
+static unsigned long quick_pit_calibrate(void)
+{
+	int i;
+	u64 tsc, delta;
+	unsigned long d1, d2;
+
+	/* Set the Gate high, disable speaker */
+	outb((inb(0x61) & ~0x02) | 0x01, 0x61);
+
+	/*
+	 * Counter 2, mode 0 (one-shot), binary count
+	 *
+	 * NOTE! Mode 2 decrements by two (and then the
+	 * output is flipped each time, giving the same
+	 * final output frequency as a decrement-by-one),
+	 * so mode 0 is much better when looking at the
+	 * individual counts.
+	 */
+	outb(0xb0, 0x43);
+
+	/* Start at 0xffff */
+	outb(0xff, 0x42);
+	outb(0xff, 0x42);
+
+	/*
+	 * The PIT starts counting at the next edge, so we
+	 * need to delay for a microsecond. The easiest way
+	 * to do that is to just read back the 16-bit counter
+	 * once from the PIT.
+	 */
+	pit_verify_msb(0);
+
+	if (pit_expect_msb(0xff, &tsc, &d1)) {
+		for (i = 1; i <= MAX_QUICK_PIT_ITERATIONS; i++) {
+			if (!pit_expect_msb(0xff-i, &delta, &d2))
+				break;
+
+			/*
+			 * Iterate until the error is less than 500 ppm
+			 */
+			delta -= tsc;
+			if (d1+d2 >= delta >> 11)
+				continue;
+
+			/*
+			 * Check the PIT one more time to verify that
+			 * all TSC reads were stable wrt the PIT.
+			 *
+			 * This also guarantees serialization of the
+			 * last cycle read ('d2') in pit_expect_msb.
+			 */
+			if (!pit_verify_msb(0xfe - i))
+				break;
+			goto success;
+		}
+	}
+	pr_info("Fast TSC calibration failed\n");
+	return 0;
+
+success:
+	/*
+	 * Ok, if we get here, then we've seen the
+	 * MSB of the PIT decrement 'i' times, and the
+	 * error has shrunk to less than 500 ppm.
+	 *
+	 * As a result, we can depend on there not being
+	 * any odd delays anywhere, and the TSC reads are
+	 * reliable (within the error).
+	 *
+	 * kHz = ticks / time-in-seconds / 1000;
+	 * kHz = (t2 - t1) / (I * 256 / PIT_TICK_RATE) / 1000
+	 * kHz = ((t2 - t1) * PIT_TICK_RATE) / (I * 256 * 1000)
+	 */
+	delta *= PIT_TICK_RATE;
+	do_div(delta, i*256*1000);
+	pr_info("Fast TSC calibration using PIT\n");
+	return delta;
+}
+
+/**
+ * native_calibrate_tsc - calibrate the tsc on boot
+ */
+unsigned long native_calibrate_tsc(void)
+{
+	u64 tsc1, tsc2, delta, ref1, ref2;
+	unsigned long tsc_pit_min = ULONG_MAX, tsc_ref_min = ULONG_MAX;
+	unsigned long flags, latch, ms, fast_calibrate;
+	int hpet = is_hpet_enabled(), i, loopmin;
+
+	/* Calibrate TSC using MSR for Intel Atom SoCs */
+	local_irq_save(flags);
+	fast_calibrate = try_msr_calibrate_tsc();
+	local_irq_restore(flags);
+	if (fast_calibrate)
+		return fast_calibrate;
+
+	local_irq_save(flags);
+	fast_calibrate = quick_pit_calibrate();
+	local_irq_restore(flags);
+	if (fast_calibrate)
+		return fast_calibrate;
+
+	/*
+	 * Run 5 calibration loops to get the lowest frequency value
+	 * (the best estimate). We use two different calibration modes
+	 * here:
+	 *
+	 * 1) PIT loop. We set the PIT Channel 2 to oneshot mode and
+	 * load a timeout of 50ms. We read the time right after we
+	 * started the timer and wait until the PIT count down reaches
+	 * zero. In each wait loop iteration we read the TSC and check
+	 * the delta to the previous read. We keep track of the min
+	 * and max values of that delta. The delta is mostly defined
+	 * by the IO time of the PIT access, so we can detect when a
+	 * SMI/SMM disturbance happened between the two reads. If the
+	 * maximum time is significantly larger than the minimum time,
+	 * then we discard the result and have another try.
+	 *
+	 * 2) Reference counter. If available we use the HPET or the
+	 * PMTIMER as a reference to check the sanity of that value.
+	 * We use separate TSC readouts and check inside of the
+	 * reference read for a SMI/SMM disturbance. We dicard
+	 * disturbed values here as well. We do that around the PIT
+	 * calibration delay loop as we have to wait for a certain
+	 * amount of time anyway.
+	 */
+
+	/* Preset PIT loop values */
+	latch = CAL_LATCH;
+	ms = CAL_MS;
+	loopmin = CAL_PIT_LOOPS;
+
+	for (i = 0; i < 3; i++) {
+		unsigned long tsc_pit_khz;
+
+		/*
+		 * Read the start value and the reference count of
+		 * hpet/pmtimer when available. Then do the PIT
+		 * calibration, which will take at least 50ms, and
+		 * read the end value.
+		 */
+		local_irq_save(flags);
+		tsc1 = tsc_read_refs(&ref1, hpet);
+		tsc_pit_khz = pit_calibrate_tsc(latch, ms, loopmin);
+		tsc2 = tsc_read_refs(&ref2, hpet);
+		local_irq_restore(flags);
+
+		/* Pick the lowest PIT TSC calibration so far */
+		tsc_pit_min = min(tsc_pit_min, tsc_pit_khz);
+
+		/* hpet or pmtimer available ? */
+		if (ref1 == ref2)
+			continue;
+
+		/* Check, whether the sampling was disturbed by an SMI */
+		if (tsc1 == ULLONG_MAX || tsc2 == ULLONG_MAX)
+			continue;
+
+		tsc2 = (tsc2 - tsc1) * 1000000LL;
+		if (hpet)
+			tsc2 = calc_hpet_ref(tsc2, ref1, ref2);
+		else
+			tsc2 = calc_pmtimer_ref(tsc2, ref1, ref2);
+
+		tsc_ref_min = min(tsc_ref_min, (unsigned long) tsc2);
+
+		/* Check the reference deviation */
+		delta = ((u64) tsc_pit_min) * 100;
+		do_div(delta, tsc_ref_min);
+
+		/*
+		 * If both calibration results are inside a 10% window
+		 * then we can be sure, that the calibration
+		 * succeeded. We break out of the loop right away. We
+		 * use the reference value, as it is more precise.
+		 */
+		if (delta >= 90 && delta <= 110) {
+			pr_info("PIT calibration matches %s. %d loops\n",
+				hpet ? "HPET" : "PMTIMER", i + 1);
+			return tsc_ref_min;
+		}
+
+		/*
+		 * Check whether PIT failed more than once. This
+		 * happens in virtualized environments. We need to
+		 * give the virtual PC a slightly longer timeframe for
+		 * the HPET/PMTIMER to make the result precise.
+		 */
+		if (i == 1 && tsc_pit_min == ULONG_MAX) {
+			latch = CAL2_LATCH;
+			ms = CAL2_MS;
+			loopmin = CAL2_PIT_LOOPS;
+		}
+	}
+
+	/*
+	 * Now check the results.
+	 */
+	if (tsc_pit_min == ULONG_MAX) {
+		/* PIT gave no useful value */
+		pr_warn("Unable to calibrate against PIT\n");
+
+		/* We don't have an alternative source, disable TSC */
+		if (!hpet && !ref1 && !ref2) {
+			pr_notice("No reference (HPET/PMTIMER) available\n");
+			return 0;
+		}
+
+		/* The alternative source failed as well, disable TSC */
+		if (tsc_ref_min == ULONG_MAX) {
+			pr_warn("HPET/PMTIMER calibration failed\n");
+			return 0;
+		}
+
+		/* Use the alternative source */
+		pr_info("using %s reference calibration\n",
+			hpet ? "HPET" : "PMTIMER");
+
+		return tsc_ref_min;
+	}
+
+	/* We don't have an alternative source, use the PIT calibration value */
+	if (!hpet && !ref1 && !ref2) {
+		pr_info("Using PIT calibration value\n");
+		return tsc_pit_min;
+	}
+
+	/* The alternative source failed, use the PIT calibration value */
+	if (tsc_ref_min == ULONG_MAX) {
+		pr_warn("HPET/PMTIMER calibration failed. Using PIT calibration.\n");
+		return tsc_pit_min;
+	}
+
+	/*
+	 * The calibration values differ too much. In doubt, we use
+	 * the PIT value as we know that there are PMTIMERs around
+	 * running at double speed. At least we let the user know:
+	 */
+	pr_warn("PIT calibration deviates from %s: %lu %lu\n",
+		hpet ? "HPET" : "PMTIMER", tsc_pit_min, tsc_ref_min);
+	pr_info("Using PIT calibration value\n");
+	return tsc_pit_min;
+}
+
+int recalibrate_cpu_khz(void)
+{
+#ifndef CONFIG_SMP
+	unsigned long cpu_khz_old = cpu_khz;
+
+	if (cpu_has_tsc) {
+		tsc_khz = x86_platform.calibrate_tsc();
+		cpu_khz = tsc_khz;
+		cpu_data(0).loops_per_jiffy =
+			cpufreq_scale(cpu_data(0).loops_per_jiffy,
+					cpu_khz_old, cpu_khz);
+		return 0;
+	} else
+		return -ENODEV;
+#else
+	return -ENODEV;
+#endif
+}
+
+EXPORT_SYMBOL(recalibrate_cpu_khz);
+
+
+static unsigned long long cyc2ns_suspend;
+
+void tsc_save_sched_clock_state(void)
+{
+	if (!sched_clock_stable())
+		return;
+
+	cyc2ns_suspend = sched_clock();
+}
+
+/*
+ * Even on processors with invariant TSC, TSC gets reset in some the
+ * ACPI system sleep states. And in some systems BIOS seem to reinit TSC to
+ * arbitrary value (still sync'd across cpu's) during resume from such sleep
+ * states. To cope up with this, recompute the cyc2ns_offset for each cpu so
+ * that sched_clock() continues from the point where it was left off during
+ * suspend.
+ */
+void tsc_restore_sched_clock_state(void)
+{
+	unsigned long long offset;
+	unsigned long flags;
+	int cpu;
+
+	if (!sched_clock_stable())
+		return;
+
+	local_irq_save(flags);
+
+	/*
+	 * We're comming out of suspend, there's no concurrency yet; don't
+	 * bother being nice about the RCU stuff, just write to both
+	 * data fields.
+	 */
+
+	this_cpu_write(cyc2ns.data[0].cyc2ns_offset, 0);
+	this_cpu_write(cyc2ns.data[1].cyc2ns_offset, 0);
+
+	offset = cyc2ns_suspend - sched_clock();
+
+	for_each_possible_cpu(cpu) {
+		per_cpu(cyc2ns.data[0].cyc2ns_offset, cpu) = offset;
+		per_cpu(cyc2ns.data[1].cyc2ns_offset, cpu) = offset;
+	}
+
+	local_irq_restore(flags);
+}
+
+#ifdef CONFIG_CPU_FREQ
+
+/* Frequency scaling support. Adjust the TSC based timer when the cpu frequency
+ * changes.
+ *
+ * RED-PEN: On SMP we assume all CPUs run with the same frequency.  It's
+ * not that important because current Opteron setups do not support
+ * scaling on SMP anyroads.
+ *
+ * Should fix up last_tsc too. Currently gettimeofday in the
+ * first tick after the change will be slightly wrong.
+ */
+
+static unsigned int  ref_freq;
+static unsigned long loops_per_jiffy_ref;
+static unsigned long tsc_khz_ref;
+
+static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
+				void *data)
+{
+	struct cpufreq_freqs *freq = data;
+	unsigned long *lpj;
+
+	if (cpu_has(&cpu_data(freq->cpu), X86_FEATURE_CONSTANT_TSC))
+		return 0;
+
+	lpj = &boot_cpu_data.loops_per_jiffy;
+#ifdef CONFIG_SMP
+	if (!(freq->flags & CPUFREQ_CONST_LOOPS))
+		lpj = &cpu_data(freq->cpu).loops_per_jiffy;
+#endif
+
+	if (!ref_freq) {
+		ref_freq = freq->old;
+		loops_per_jiffy_ref = *lpj;
+		tsc_khz_ref = tsc_khz;
+	}
+	if ((val == CPUFREQ_PRECHANGE  && freq->old < freq->new) ||
+			(val == CPUFREQ_POSTCHANGE && freq->old > freq->new)) {
+		*lpj = cpufreq_scale(loops_per_jiffy_ref, ref_freq, freq->new);
+
+		tsc_khz = cpufreq_scale(tsc_khz_ref, ref_freq, freq->new);
+		if (!(freq->flags & CPUFREQ_CONST_LOOPS))
+			mark_tsc_unstable("cpufreq changes");
+
+		set_cyc2ns_scale(tsc_khz, freq->cpu);
+	}
+
+	return 0;
+}
+
+static struct notifier_block time_cpufreq_notifier_block = {
+	.notifier_call  = time_cpufreq_notifier
+};
+
+static int __init cpufreq_tsc(void)
+{
+	if (!cpu_has_tsc)
+		return 0;
+	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
+		return 0;
+	cpufreq_register_notifier(&time_cpufreq_notifier_block,
+				CPUFREQ_TRANSITION_NOTIFIER);
+	return 0;
+}
+
+core_initcall(cpufreq_tsc);
+
+#endif /* CONFIG_CPU_FREQ */
+
+/* clocksource code */
+
+static struct clocksource clocksource_tsc;
+
+/*
+ * We used to compare the TSC to the cycle_last value in the clocksource
+ * structure to avoid a nasty time-warp. This can be observed in a
+ * very small window right after one CPU updated cycle_last under
+ * xtime/vsyscall_gtod lock and the other CPU reads a TSC value which
+ * is smaller than the cycle_last reference value due to a TSC which
+ * is slighty behind. This delta is nowhere else observable, but in
+ * that case it results in a forward time jump in the range of hours
+ * due to the unsigned delta calculation of the time keeping core
+ * code, which is necessary to support wrapping clocksources like pm
+ * timer.
+ *
+ * This sanity check is now done in the core timekeeping code.
+ * checking the result of read_tsc() - cycle_last for being negative.
+ * That works because CLOCKSOURCE_MASK(64) does not mask out any bit.
+ */
+static cycle_t read_tsc(struct clocksource *cs)
+{
+	return (cycle_t)get_cycles();
+}
+
+/*
+ * .mask MUST be CLOCKSOURCE_MASK(64). See comment above read_tsc()
+ */
+static struct clocksource clocksource_tsc = {
+	.name                   = "tsc",
+	.rating                 = 300,
+	.read                   = read_tsc,
+	.mask                   = CLOCKSOURCE_MASK(64),
+	.flags                  = CLOCK_SOURCE_IS_CONTINUOUS |
+				  CLOCK_SOURCE_MUST_VERIFY,
+	.archdata               = { .vclock_mode = VCLOCK_TSC },
+};
+
+void mark_tsc_unstable(char *reason)
+{
+	if (!tsc_unstable) {
+		tsc_unstable = 1;
+		clear_sched_clock_stable();
+		disable_sched_clock_irqtime();
+		pr_info("Marking TSC unstable due to %s\n", reason);
+		/* Change only the rating, when not registered */
+		if (clocksource_tsc.mult)
+			clocksource_mark_unstable(&clocksource_tsc);
+		else {
+			clocksource_tsc.flags |= CLOCK_SOURCE_UNSTABLE;
+			clocksource_tsc.rating = 0;
+		}
+	}
+}
+
+EXPORT_SYMBOL_GPL(mark_tsc_unstable);
+
+static void __init check_system_tsc_reliable(void)
+{
+#ifdef CONFIG_MGEODE_LX
+	/* RTSC counts during suspend */
+#define RTSC_SUSP 0x100
+	unsigned long res_low, res_high;
+
+	rdmsr_safe(MSR_GEODE_BUSCONT_CONF0, &res_low, &res_high);
+	/* Geode_LX - the OLPC CPU has a very reliable TSC */
+	if (res_low & RTSC_SUSP)
+		tsc_clocksource_reliable = 1;
+#endif
+	if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE))
+		tsc_clocksource_reliable = 1;
+}
+
+/*
+ * Make an educated guess if the TSC is trustworthy and synchronized
+ * over all CPUs.
+ */
+int unsynchronized_tsc(void)
+{
+	if (!cpu_has_tsc || tsc_unstable)
+		return 1;
+
+#ifdef CONFIG_SMP
+	if (apic_is_clustered_box())
+		return 1;
+#endif
+
+	if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
+		return 0;
+
+	if (tsc_clocksource_reliable)
+		return 0;
+	/*
+	 * Intel systems are normally all synchronized.
+	 * Exceptions must mark TSC as unstable:
+	 */
+	if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
+		/* assume multi socket systems are not synchronized: */
+		if (num_possible_cpus() > 1)
+			return 1;
+	}
+
+	return 0;
+}
+
+
+static void tsc_refine_calibration_work(struct work_struct *work);
+static DECLARE_DELAYED_WORK(tsc_irqwork, tsc_refine_calibration_work);
+/**
+ * tsc_refine_calibration_work - Further refine tsc freq calibration
+ * @work - ignored.
+ *
+ * This functions uses delayed work over a period of a
+ * second to further refine the TSC freq value. Since this is
+ * timer based, instead of loop based, we don't block the boot
+ * process while this longer calibration is done.
+ *
+ * If there are any calibration anomalies (too many SMIs, etc),
+ * or the refined calibration is off by 1% of the fast early
+ * calibration, we throw out the new calibration and use the
+ * early calibration.
+ */
+static void tsc_refine_calibration_work(struct work_struct *work)
+{
+	static u64 tsc_start = -1, ref_start;
+	static int hpet;
+	u64 tsc_stop, ref_stop, delta;
+	unsigned long freq;
+
+	/* Don't bother refining TSC on unstable systems */
+	if (check_tsc_unstable())
+		goto out;
+
+	/*
+	 * Since the work is started early in boot, we may be
+	 * delayed the first time we expire. So set the workqueue
+	 * again once we know timers are working.
+	 */
+	if (tsc_start == -1) {
+		/*
+		 * Only set hpet once, to avoid mixing hardware
+		 * if the hpet becomes enabled later.
+		 */
+		hpet = is_hpet_enabled();
+		schedule_delayed_work(&tsc_irqwork, HZ);
+		tsc_start = tsc_read_refs(&ref_start, hpet);
+		return;
+	}
+
+	tsc_stop = tsc_read_refs(&ref_stop, hpet);
+
+	/* hpet or pmtimer available ? */
+	if (ref_start == ref_stop)
+		goto out;
+
+	/* Check, whether the sampling was disturbed by an SMI */
+	if (tsc_start == ULLONG_MAX || tsc_stop == ULLONG_MAX)
+		goto out;
+
+	delta = tsc_stop - tsc_start;
+	delta *= 1000000LL;
+	if (hpet)
+		freq = calc_hpet_ref(delta, ref_start, ref_stop);
+	else
+		freq = calc_pmtimer_ref(delta, ref_start, ref_stop);
+
+	/* Make sure we're within 1% */
+	if (abs(tsc_khz - freq) > tsc_khz/100)
+		goto out;
+
+	tsc_khz = freq;
+	pr_info("Refined TSC clocksource calibration: %lu.%03lu MHz\n",
+		(unsigned long)tsc_khz / 1000,
+		(unsigned long)tsc_khz % 1000);
+
+out:
+	clocksource_register_khz(&clocksource_tsc, tsc_khz);
+}
+
+
+static int __init init_tsc_clocksource(void)
+{
+	if (!cpu_has_tsc || tsc_disabled > 0 || !tsc_khz)
+		return 0;
+
+	if (tsc_clocksource_reliable)
+		clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
+	/* lower the rating if we already know its unstable: */
+	if (check_tsc_unstable()) {
+		clocksource_tsc.rating = 0;
+		clocksource_tsc.flags &= ~CLOCK_SOURCE_IS_CONTINUOUS;
+	}
+
+	if (boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3))
+		clocksource_tsc.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP;
+
+	/*
+	 * Trust the results of the earlier calibration on systems
+	 * exporting a reliable TSC.
+	 */
+	if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {
+		clocksource_register_khz(&clocksource_tsc, tsc_khz);
+		return 0;
+	}
+
+	schedule_delayed_work(&tsc_irqwork, 0);
+	return 0;
+}
+/*
+ * We use device_initcall here, to ensure we run after the hpet
+ * is fully initialized, which may occur at fs_initcall time.
+ */
+device_initcall(init_tsc_clocksource);
+
+void __init tsc_init(void)
+{
+	u64 lpj;
+	int cpu;
+
+	x86_init.timers.tsc_pre_init();
+
+	if (!cpu_has_tsc) {
+		setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
+		return;
+	}
+
+	tsc_khz = x86_platform.calibrate_tsc();
+	cpu_khz = tsc_khz;
+
+	if (!tsc_khz) {
+		mark_tsc_unstable("could not calculate TSC khz");
+		setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER);
+		return;
+	}
+
+	pr_info("Detected %lu.%03lu MHz processor\n",
+		(unsigned long)cpu_khz / 1000,
+		(unsigned long)cpu_khz % 1000);
+
+	/*
+	 * Secondary CPUs do not run through tsc_init(), so set up
+	 * all the scale factors for all CPUs, assuming the same
+	 * speed as the bootup CPU. (cpufreq notifiers will fix this
+	 * up if their speed diverges)
+	 */
+	for_each_possible_cpu(cpu) {
+		cyc2ns_init(cpu);
+		set_cyc2ns_scale(cpu_khz, cpu);
+	}
+
+	if (tsc_disabled > 0)
+		return;
+
+	/* now allow native_sched_clock() to use rdtsc */
+
+	tsc_disabled = 0;
+	static_key_slow_inc(&__use_tsc);
+
+	if (!no_sched_irq_time)
+		enable_sched_clock_irqtime();
+
+	lpj = ((u64)tsc_khz * 1000);
+	do_div(lpj, HZ);
+	lpj_fine = lpj;
+
+	use_tsc_delay();
+
+	if (unsynchronized_tsc())
+		mark_tsc_unstable("TSCs unsynchronized");
+
+	check_system_tsc_reliable();
+}
+
+#ifdef CONFIG_SMP
+/*
+ * If we have a constant TSC and are using the TSC for the delay loop,
+ * we can skip clock calibration if another cpu in the same socket has already
+ * been calibrated. This assumes that CONSTANT_TSC applies to all
+ * cpus in the socket - this should be a safe assumption.
+ */
+unsigned long calibrate_delay_is_known(void)
+{
+	int i, cpu = smp_processor_id();
+
+	if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC))
+		return 0;
+
+	for_each_online_cpu(i)
+		if (cpu_data(i).phys_proc_id == cpu_data(cpu).phys_proc_id)
+			return cpu_data(i).loops_per_jiffy;
+	return 0;
+}
+#endif