2 * apb_timer.c: Driver for Langwell APB timers
4 * (C) Copyright 2009 Intel Corporation
5 * Author: Jacob Pan (jacob.jun.pan@intel.com)
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public License
9 * as published by the Free Software Foundation; version 2
13 * Langwell is the south complex of Intel Moorestown MID platform. There are
14 * eight external timers in total that can be used by the operating system.
15 * The timer information, such as frequency and addresses, is provided to the
17 * Timer interrupts are routed via FW/HW emulated IOAPIC independently via
18 * individual redirection table entries (RTE).
19 * Unlike HPET, there is no master counter, therefore one of the timers are
20 * used as clocksource. The overall allocation looks like:
21 * - timer 0 - NR_CPUs for per cpu timer
22 * - one timer for clocksource
23 * - one timer for watchdog driver.
24 * It is also worth notice that APB timer does not support true one-shot mode,
25 * free-running mode will be used here to emulate one-shot mode.
26 * APB timer can also be used as broadcast timer along with per cpu local APIC
27 * timer, but by default APB timer has higher rating than local APIC timers.
30 #include <linux/clocksource.h>
31 #include <linux/clockchips.h>
32 #include <linux/delay.h>
33 #include <linux/errno.h>
34 #include <linux/init.h>
35 #include <linux/sysdev.h>
36 #include <linux/slab.h>
38 #include <linux/pci.h>
39 #include <linux/sfi.h>
40 #include <linux/interrupt.h>
41 #include <linux/cpu.h>
42 #include <linux/irq.h>
44 #include <asm/fixmap.h>
45 #include <asm/apb_timer.h>
48 #define APBT_MASK CLOCKSOURCE_MASK(32)
50 #define APBT_CLOCKEVENT_RATING 110
51 #define APBT_CLOCKSOURCE_RATING 250
52 #define APBT_MIN_DELTA_USEC 200
54 #define EVT_TO_APBT_DEV(evt) container_of(evt, struct apbt_dev, evt)
55 #define APBT_CLOCKEVENT0_NUM (0)
56 #define APBT_CLOCKEVENT1_NUM (1)
57 #define APBT_CLOCKSOURCE_NUM (2)
59 static unsigned long apbt_address
;
60 static int apb_timer_block_enabled
;
61 static void __iomem
*apbt_virt_address
;
62 static int phy_cs_timer_id
;
65 * Common DW APB timer info
67 static uint64_t apbt_freq
;
69 static void apbt_set_mode(enum clock_event_mode mode
,
70 struct clock_event_device
*evt
);
71 static int apbt_next_event(unsigned long delta
,
72 struct clock_event_device
*evt
);
73 static cycle_t
apbt_read_clocksource(struct clocksource
*cs
);
74 static void apbt_restart_clocksource(struct clocksource
*cs
);
77 struct clock_event_device evt
;
87 static DEFINE_PER_CPU(struct apbt_dev
, cpu_apbt_dev
);
90 static unsigned int apbt_num_timers_used
;
91 static struct apbt_dev
*apbt_devs
;
94 static inline unsigned long apbt_readl_reg(unsigned long a
)
96 return readl(apbt_virt_address
+ a
);
99 static inline void apbt_writel_reg(unsigned long d
, unsigned long a
)
101 writel(d
, apbt_virt_address
+ a
);
104 static inline unsigned long apbt_readl(int n
, unsigned long a
)
106 return readl(apbt_virt_address
+ a
+ n
* APBTMRS_REG_SIZE
);
109 static inline void apbt_writel(int n
, unsigned long d
, unsigned long a
)
111 writel(d
, apbt_virt_address
+ a
+ n
* APBTMRS_REG_SIZE
);
114 static inline void apbt_set_mapping(void)
116 struct sfi_timer_table_entry
*mtmr
;
118 if (apbt_virt_address
) {
119 pr_debug("APBT base already mapped\n");
122 mtmr
= sfi_get_mtmr(APBT_CLOCKEVENT0_NUM
);
124 printk(KERN_ERR
"Failed to get MTMR %d from SFI\n",
125 APBT_CLOCKEVENT0_NUM
);
128 apbt_address
= (unsigned long)mtmr
->phys_addr
;
130 printk(KERN_WARNING
"No timer base from SFI, use default\n");
131 apbt_address
= APBT_DEFAULT_BASE
;
133 apbt_virt_address
= ioremap_nocache(apbt_address
, APBT_MMAP_SIZE
);
134 if (apbt_virt_address
) {
135 pr_debug("Mapped APBT physical addr %p at virtual addr %p\n",\
136 (void *)apbt_address
, (void *)apbt_virt_address
);
138 pr_debug("Failed mapping APBT phy address at %p\n",\
139 (void *)apbt_address
);
142 apbt_freq
= mtmr
->freq_hz
/ USEC_PER_SEC
;
145 /* Now figure out the physical timer id for clocksource device */
146 mtmr
= sfi_get_mtmr(APBT_CLOCKSOURCE_NUM
);
150 /* Now figure out the physical timer id */
151 phy_cs_timer_id
= (unsigned int)(mtmr
->phys_addr
& 0xff)
153 pr_debug("Use timer %d for clocksource\n", phy_cs_timer_id
);
157 panic("Failed to setup APB system timer\n");
161 static inline void apbt_clear_mapping(void)
163 iounmap(apbt_virt_address
);
164 apbt_virt_address
= NULL
;
168 * APBT timer interrupt enable / disable
170 static inline int is_apbt_capable(void)
172 return apbt_virt_address
? 1 : 0;
175 static struct clocksource clocksource_apbt
= {
177 .rating
= APBT_CLOCKSOURCE_RATING
,
178 .read
= apbt_read_clocksource
,
181 .flags
= CLOCK_SOURCE_IS_CONTINUOUS
,
182 .resume
= apbt_restart_clocksource
,
185 /* boot APB clock event device */
186 static struct clock_event_device apbt_clockevent
= {
188 .features
= CLOCK_EVT_FEAT_PERIODIC
| CLOCK_EVT_FEAT_ONESHOT
,
189 .set_mode
= apbt_set_mode
,
190 .set_next_event
= apbt_next_event
,
193 .rating
= APBT_CLOCKEVENT_RATING
,
197 * start count down from 0xffff_ffff. this is done by toggling the enable bit
198 * then load initial load count to ~0.
200 static void apbt_start_counter(int n
)
202 unsigned long ctrl
= apbt_readl(n
, APBTMR_N_CONTROL
);
204 ctrl
&= ~APBTMR_CONTROL_ENABLE
;
205 apbt_writel(n
, ctrl
, APBTMR_N_CONTROL
);
206 apbt_writel(n
, ~0, APBTMR_N_LOAD_COUNT
);
207 /* enable, mask interrupt */
208 ctrl
&= ~APBTMR_CONTROL_MODE_PERIODIC
;
209 ctrl
|= (APBTMR_CONTROL_ENABLE
| APBTMR_CONTROL_INT
);
210 apbt_writel(n
, ctrl
, APBTMR_N_CONTROL
);
211 /* read it once to get cached counter value initialized */
212 apbt_read_clocksource(&clocksource_apbt
);
215 static irqreturn_t
apbt_interrupt_handler(int irq
, void *data
)
217 struct apbt_dev
*dev
= (struct apbt_dev
*)data
;
218 struct clock_event_device
*aevt
= &dev
->evt
;
220 if (!aevt
->event_handler
) {
221 printk(KERN_INFO
"Spurious APBT timer interrupt on %d\n",
225 aevt
->event_handler(aevt
);
229 static void apbt_restart_clocksource(struct clocksource
*cs
)
231 apbt_start_counter(phy_cs_timer_id
);
234 static void apbt_enable_int(int n
)
236 unsigned long ctrl
= apbt_readl(n
, APBTMR_N_CONTROL
);
237 /* clear pending intr */
238 apbt_readl(n
, APBTMR_N_EOI
);
239 ctrl
&= ~APBTMR_CONTROL_INT
;
240 apbt_writel(n
, ctrl
, APBTMR_N_CONTROL
);
243 static void apbt_disable_int(int n
)
245 unsigned long ctrl
= apbt_readl(n
, APBTMR_N_CONTROL
);
247 ctrl
|= APBTMR_CONTROL_INT
;
248 apbt_writel(n
, ctrl
, APBTMR_N_CONTROL
);
252 static int __init
apbt_clockevent_register(void)
254 struct sfi_timer_table_entry
*mtmr
;
255 struct apbt_dev
*adev
= &__get_cpu_var(cpu_apbt_dev
);
257 mtmr
= sfi_get_mtmr(APBT_CLOCKEVENT0_NUM
);
259 printk(KERN_ERR
"Failed to get MTMR %d from SFI\n",
260 APBT_CLOCKEVENT0_NUM
);
265 * We need to calculate the scaled math multiplication factor for
266 * nanosecond to apbt tick conversion.
267 * mult = (nsec/cycle)*2^APBT_SHIFT
269 apbt_clockevent
.mult
= div_sc((unsigned long) mtmr
->freq_hz
270 , NSEC_PER_SEC
, APBT_SHIFT
);
272 /* Calculate the min / max delta */
273 apbt_clockevent
.max_delta_ns
= clockevent_delta2ns(0x7FFFFFFF,
275 apbt_clockevent
.min_delta_ns
= clockevent_delta2ns(
276 APBT_MIN_DELTA_USEC
*apbt_freq
,
279 * Start apbt with the boot cpu mask and make it
280 * global if not used for per cpu timer.
282 apbt_clockevent
.cpumask
= cpumask_of(smp_processor_id());
283 adev
->num
= smp_processor_id();
284 memcpy(&adev
->evt
, &apbt_clockevent
, sizeof(struct clock_event_device
));
286 if (mrst_timer_options
== MRST_TIMER_LAPIC_APBT
) {
287 apbt_clockevent
.rating
= APBT_CLOCKEVENT_RATING
- 100;
288 global_clock_event
= &adev
->evt
;
289 printk(KERN_DEBUG
"%s clockevent registered as global\n",
290 global_clock_event
->name
);
293 if (request_irq(apbt_clockevent
.irq
, apbt_interrupt_handler
,
294 IRQF_TIMER
| IRQF_DISABLED
| IRQF_NOBALANCING
,
295 apbt_clockevent
.name
, adev
)) {
296 printk(KERN_ERR
"Failed request IRQ for APBT%d\n",
297 apbt_clockevent
.irq
);
300 clockevents_register_device(&adev
->evt
);
301 /* Start APBT 0 interrupts */
302 apbt_enable_int(APBT_CLOCKEVENT0_NUM
);
310 static void apbt_setup_irq(struct apbt_dev
*adev
)
312 /* timer0 irq has been setup early */
316 if (system_state
== SYSTEM_BOOTING
) {
317 irq_modify_status(adev
->irq
, 0, IRQ_MOVE_PCNTXT
);
318 /* APB timer irqs are set up as mp_irqs, timer is edge type */
319 __set_irq_handler(adev
->irq
, handle_edge_irq
, 0, "edge");
320 if (request_irq(adev
->irq
, apbt_interrupt_handler
,
321 IRQF_TIMER
| IRQF_DISABLED
| IRQF_NOBALANCING
,
323 printk(KERN_ERR
"Failed request IRQ for APBT%d\n",
327 enable_irq(adev
->irq
);
330 /* Should be called with per cpu */
331 void apbt_setup_secondary_clock(void)
333 struct apbt_dev
*adev
;
334 struct clock_event_device
*aevt
;
337 /* Don't register boot CPU clockevent */
338 cpu
= smp_processor_id();
342 * We need to calculate the scaled math multiplication factor for
343 * nanosecond to apbt tick conversion.
344 * mult = (nsec/cycle)*2^APBT_SHIFT
346 printk(KERN_INFO
"Init per CPU clockevent %d\n", cpu
);
347 adev
= &per_cpu(cpu_apbt_dev
, cpu
);
350 memcpy(aevt
, &apbt_clockevent
, sizeof(*aevt
));
351 aevt
->cpumask
= cpumask_of(cpu
);
352 aevt
->name
= adev
->name
;
353 aevt
->mode
= CLOCK_EVT_MODE_UNUSED
;
355 printk(KERN_INFO
"Registering CPU %d clockevent device %s, mask %08x\n",
356 cpu
, aevt
->name
, *(u32
*)aevt
->cpumask
);
358 apbt_setup_irq(adev
);
360 clockevents_register_device(aevt
);
362 apbt_enable_int(cpu
);
368 * this notify handler process CPU hotplug events. in case of S0i3, nonboot
369 * cpus are disabled/enabled frequently, for performance reasons, we keep the
370 * per cpu timer irq registered so that we do need to do free_irq/request_irq.
372 * TODO: it might be more reliable to directly disable percpu clockevent device
373 * without the notifier chain. currently, cpu 0 may get interrupts from other
374 * cpu timers during the offline process due to the ordering of notification.
375 * the extra interrupt is harmless.
377 static int apbt_cpuhp_notify(struct notifier_block
*n
,
378 unsigned long action
, void *hcpu
)
380 unsigned long cpu
= (unsigned long)hcpu
;
381 struct apbt_dev
*adev
= &per_cpu(cpu_apbt_dev
, cpu
);
383 switch (action
& 0xf) {
385 disable_irq(adev
->irq
);
386 apbt_disable_int(cpu
);
387 if (system_state
== SYSTEM_RUNNING
) {
388 pr_debug("skipping APBT CPU %lu offline\n", cpu
);
390 pr_debug("APBT clockevent for cpu %lu offline\n", cpu
);
391 free_irq(adev
->irq
, adev
);
395 pr_debug("APBT notified %lu, no action\n", action
);
400 static __init
int apbt_late_init(void)
402 if (mrst_timer_options
== MRST_TIMER_LAPIC_APBT
||
403 !apb_timer_block_enabled
)
405 /* This notifier should be called after workqueue is ready */
406 hotcpu_notifier(apbt_cpuhp_notify
, -20);
409 fs_initcall(apbt_late_init
);
412 void apbt_setup_secondary_clock(void) {}
414 #endif /* CONFIG_SMP */
416 static void apbt_set_mode(enum clock_event_mode mode
,
417 struct clock_event_device
*evt
)
422 struct apbt_dev
*adev
= EVT_TO_APBT_DEV(evt
);
424 BUG_ON(!apbt_virt_address
);
426 timer_num
= adev
->num
;
427 pr_debug("%s CPU %d timer %d mode=%d\n",
428 __func__
, first_cpu(*evt
->cpumask
), timer_num
, mode
);
431 case CLOCK_EVT_MODE_PERIODIC
:
432 delta
= ((uint64_t)(NSEC_PER_SEC
/HZ
)) * apbt_clockevent
.mult
;
433 delta
>>= apbt_clockevent
.shift
;
434 ctrl
= apbt_readl(timer_num
, APBTMR_N_CONTROL
);
435 ctrl
|= APBTMR_CONTROL_MODE_PERIODIC
;
436 apbt_writel(timer_num
, ctrl
, APBTMR_N_CONTROL
);
438 * DW APB p. 46, have to disable timer before load counter,
439 * may cause sync problem.
441 ctrl
&= ~APBTMR_CONTROL_ENABLE
;
442 apbt_writel(timer_num
, ctrl
, APBTMR_N_CONTROL
);
444 pr_debug("Setting clock period %d for HZ %d\n", (int)delta
, HZ
);
445 apbt_writel(timer_num
, delta
, APBTMR_N_LOAD_COUNT
);
446 ctrl
|= APBTMR_CONTROL_ENABLE
;
447 apbt_writel(timer_num
, ctrl
, APBTMR_N_CONTROL
);
449 /* APB timer does not have one-shot mode, use free running mode */
450 case CLOCK_EVT_MODE_ONESHOT
:
451 ctrl
= apbt_readl(timer_num
, APBTMR_N_CONTROL
);
453 * set free running mode, this mode will let timer reload max
454 * timeout which will give time (3min on 25MHz clock) to rearm
455 * the next event, therefore emulate the one-shot mode.
457 ctrl
&= ~APBTMR_CONTROL_ENABLE
;
458 ctrl
&= ~APBTMR_CONTROL_MODE_PERIODIC
;
460 apbt_writel(timer_num
, ctrl
, APBTMR_N_CONTROL
);
461 /* write again to set free running mode */
462 apbt_writel(timer_num
, ctrl
, APBTMR_N_CONTROL
);
465 * DW APB p. 46, load counter with all 1s before starting free
468 apbt_writel(timer_num
, ~0, APBTMR_N_LOAD_COUNT
);
469 ctrl
&= ~APBTMR_CONTROL_INT
;
470 ctrl
|= APBTMR_CONTROL_ENABLE
;
471 apbt_writel(timer_num
, ctrl
, APBTMR_N_CONTROL
);
474 case CLOCK_EVT_MODE_UNUSED
:
475 case CLOCK_EVT_MODE_SHUTDOWN
:
476 apbt_disable_int(timer_num
);
477 ctrl
= apbt_readl(timer_num
, APBTMR_N_CONTROL
);
478 ctrl
&= ~APBTMR_CONTROL_ENABLE
;
479 apbt_writel(timer_num
, ctrl
, APBTMR_N_CONTROL
);
482 case CLOCK_EVT_MODE_RESUME
:
483 apbt_enable_int(timer_num
);
488 static int apbt_next_event(unsigned long delta
,
489 struct clock_event_device
*evt
)
494 struct apbt_dev
*adev
= EVT_TO_APBT_DEV(evt
);
496 timer_num
= adev
->num
;
498 ctrl
= apbt_readl(timer_num
, APBTMR_N_CONTROL
);
499 ctrl
&= ~APBTMR_CONTROL_ENABLE
;
500 apbt_writel(timer_num
, ctrl
, APBTMR_N_CONTROL
);
501 /* write new count */
502 apbt_writel(timer_num
, delta
, APBTMR_N_LOAD_COUNT
);
503 ctrl
|= APBTMR_CONTROL_ENABLE
;
504 apbt_writel(timer_num
, ctrl
, APBTMR_N_CONTROL
);
509 * APB timer clock is not in sync with pclk on Langwell, which translates to
510 * unreliable read value caused by sampling error. the error does not add up
511 * overtime and only happens when sampling a 0 as a 1 by mistake. so the time
512 * would go backwards. the following code is trying to prevent time traveling
513 * backwards. little bit paranoid.
515 static cycle_t
apbt_read_clocksource(struct clocksource
*cs
)
517 unsigned long t0
, t1
, t2
;
518 static unsigned long last_read
;
521 t1
= apbt_readl(phy_cs_timer_id
,
522 APBTMR_N_CURRENT_VALUE
);
523 t2
= apbt_readl(phy_cs_timer_id
,
524 APBTMR_N_CURRENT_VALUE
);
525 if (unlikely(t1
< t2
)) {
526 pr_debug("APBT: read current count error %lx:%lx:%lx\n",
531 * check against cached last read, makes sure time does not go back.
532 * it could be a normal rollover but we will do tripple check anyway
534 if (unlikely(t2
> last_read
)) {
535 /* check if we have a normal rollover */
536 unsigned long raw_intr_status
=
537 apbt_readl_reg(APBTMRS_RAW_INT_STATUS
);
539 * cs timer interrupt is masked but raw intr bit is set if
540 * rollover occurs. then we read EOI reg to clear it.
542 if (raw_intr_status
& (1 << phy_cs_timer_id
)) {
543 apbt_readl(phy_cs_timer_id
, APBTMR_N_EOI
);
546 pr_debug("APB CS going back %lx:%lx:%lx ",
547 t2
, last_read
, t2
- last_read
);
549 pr_debug("triple check enforced\n");
550 t0
= apbt_readl(phy_cs_timer_id
,
551 APBTMR_N_CURRENT_VALUE
);
553 t1
= apbt_readl(phy_cs_timer_id
,
554 APBTMR_N_CURRENT_VALUE
);
556 t2
= apbt_readl(phy_cs_timer_id
,
557 APBTMR_N_CURRENT_VALUE
);
558 if ((t2
> t1
) || (t1
> t0
)) {
559 printk(KERN_ERR
"Error: APB CS tripple check failed\n");
568 static int apbt_clocksource_register(void)
573 /* Start the counter, use timer 2 as source, timer 0/1 for event */
574 apbt_start_counter(phy_cs_timer_id
);
576 /* Verify whether apbt counter works */
577 t1
= apbt_read_clocksource(&clocksource_apbt
);
581 * We don't know the TSC frequency yet, but waiting for
582 * 200000 TSC cycles is safe:
589 } while ((now
- start
) < 200000UL);
591 /* APBT is the only always on clocksource, it has to work! */
592 if (t1
== apbt_read_clocksource(&clocksource_apbt
))
593 panic("APBT counter not counting. APBT disabled\n");
596 * initialize and register APBT clocksource
597 * convert that to ns/clock cycle
598 * mult = (ns/c) * 2^APBT_SHIFT
600 clocksource_apbt
.mult
= div_sc(MSEC_PER_SEC
,
601 (unsigned long) apbt_freq
, APBT_SHIFT
);
602 clocksource_register(&clocksource_apbt
);
608 * Early setup the APBT timer, only use timer 0 for booting then switch to
609 * per CPU timer if possible.
610 * returns 1 if per cpu apbt is setup
611 * returns 0 if no per cpu apbt is chosen
612 * panic if set up failed, this is the only platform timer on Moorestown.
614 void __init
apbt_time_init(void)
618 struct sfi_timer_table_entry
*p_mtmr
;
619 unsigned int percpu_timer
;
620 struct apbt_dev
*adev
;
623 if (apb_timer_block_enabled
)
626 if (apbt_virt_address
) {
627 pr_debug("Found APBT version 0x%lx\n",\
628 apbt_readl_reg(APBTMRS_COMP_VERSION
));
632 * Read the frequency and check for a sane value, for ESL model
633 * we extend the possible clock range to allow time scaling.
636 if (apbt_freq
< APBT_MIN_FREQ
|| apbt_freq
> APBT_MAX_FREQ
) {
637 pr_debug("APBT has invalid freq 0x%llx\n", apbt_freq
);
640 if (apbt_clocksource_register()) {
641 pr_debug("APBT has failed to register clocksource\n");
644 if (!apbt_clockevent_register())
645 apb_timer_block_enabled
= 1;
647 pr_debug("APBT has failed to register clockevent\n");
651 /* kernel cmdline disable apb timer, so we will use lapic timers */
652 if (mrst_timer_options
== MRST_TIMER_LAPIC_APBT
) {
653 printk(KERN_INFO
"apbt: disabled per cpu timer\n");
656 pr_debug("%s: %d CPUs online\n", __func__
, num_online_cpus());
657 if (num_possible_cpus() <= sfi_mtimer_num
) {
659 apbt_num_timers_used
= num_possible_cpus();
662 apbt_num_timers_used
= 1;
663 adev
= &per_cpu(cpu_apbt_dev
, 0);
664 adev
->flags
&= ~APBT_DEV_USED
;
666 pr_debug("%s: %d APB timers used\n", __func__
, apbt_num_timers_used
);
668 /* here we set up per CPU timer data structure */
669 apbt_devs
= kzalloc(sizeof(struct apbt_dev
) * apbt_num_timers_used
,
672 printk(KERN_ERR
"Failed to allocate APB timer devices\n");
675 for (i
= 0; i
< apbt_num_timers_used
; i
++) {
676 adev
= &per_cpu(cpu_apbt_dev
, i
);
679 p_mtmr
= sfi_get_mtmr(i
);
681 adev
->tick
= p_mtmr
->freq_hz
;
682 adev
->irq
= p_mtmr
->irq
;
684 printk(KERN_ERR
"Failed to get timer for cpu %d\n", i
);
686 sprintf(adev
->name
, "apbt%d", i
);
693 apbt_clear_mapping();
694 apb_timer_block_enabled
= 0;
695 panic("failed to enable APB timer\n");
698 static inline void apbt_disable(int n
)
700 if (is_apbt_capable()) {
701 unsigned long ctrl
= apbt_readl(n
, APBTMR_N_CONTROL
);
702 ctrl
&= ~APBTMR_CONTROL_ENABLE
;
703 apbt_writel(n
, ctrl
, APBTMR_N_CONTROL
);
707 /* called before apb_timer_enable, use early map */
708 unsigned long apbt_quick_calibrate()
713 unsigned long khz
= 0;
717 apbt_start_counter(phy_cs_timer_id
);
719 /* check if the timer can count down, otherwise return */
720 old
= apbt_read_clocksource(&clocksource_apbt
);
723 if (old
!= apbt_read_clocksource(&clocksource_apbt
))
730 loop
= (apbt_freq
* 1000) << 4;
732 /* restart the timer to ensure it won't get to 0 in the calibration */
733 apbt_start_counter(phy_cs_timer_id
);
735 old
= apbt_read_clocksource(&clocksource_apbt
);
738 t1
= __native_read_tsc();
741 new = apbt_read_clocksource(&clocksource_apbt
);
744 t2
= __native_read_tsc();
747 if (unlikely(loop
>> shift
== 0)) {
749 "APBT TSC calibration failed, not enough resolution\n");
752 scale
= (int)div_u64((t2
- t1
), loop
>> shift
);
753 khz
= (scale
* apbt_freq
* 1000) >> shift
;
754 printk(KERN_INFO
"TSC freq calculated by APB timer is %lu khz\n", khz
);