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11#include <linux/errno.h>
12#include <linux/module.h>
13#include <linux/sched.h>
14#include <linux/kernel.h>
15#include <linux/param.h>
16#include <linux/string.h>
17#include <linux/mm.h>
18#include <linux/interrupt.h>
19#include <linux/time.h>
20#include <linux/timex.h>
21#include <linux/init.h>
22#include <linux/ioport.h>
23#include <linux/mc146818rtc.h>
24#include <linux/delay.h>
25#include <linux/profile.h>
26#include <linux/bcd.h>
27#include <linux/jiffies.h>
28#include <linux/cpufreq.h>
29#include <linux/percpu.h>
30#include <linux/miscdevice.h>
31#include <linux/rtc.h>
32#include <linux/rtc/m48t59.h>
33#include <linux/kernel_stat.h>
34#include <linux/clockchips.h>
35#include <linux/clocksource.h>
36#include <linux/of_device.h>
37#include <linux/platform_device.h>
38#include <linux/ftrace.h>
39
40#include <asm/oplib.h>
41#include <asm/timer.h>
42#include <asm/irq.h>
43#include <asm/io.h>
44#include <asm/prom.h>
45#include <asm/starfire.h>
46#include <asm/smp.h>
47#include <asm/sections.h>
48#include <asm/cpudata.h>
49#include <asm/uaccess.h>
50#include <asm/irq_regs.h>
51
52#include "entry.h"
53
54DEFINE_SPINLOCK(rtc_lock);
55
56#define TICK_PRIV_BIT (1UL << 63)
57#define TICKCMP_IRQ_BIT (1UL << 63)
58
59#ifdef CONFIG_SMP
60unsigned long profile_pc(struct pt_regs *regs)
61{
62 unsigned long pc = instruction_pointer(regs);
63
64 if (in_lock_functions(pc))
65 return regs->u_regs[UREG_RETPC];
66 return pc;
67}
68EXPORT_SYMBOL(profile_pc);
69#endif
70
71static void tick_disable_protection(void)
72{
73
74
75
76
77 __asm__ __volatile__(
78 " ba,pt %%xcc, 1f\n"
79 " nop\n"
80 " .align 64\n"
81 "1: rd %%tick, %%g2\n"
82 " add %%g2, 6, %%g2\n"
83 " andn %%g2, %0, %%g2\n"
84 " wrpr %%g2, 0, %%tick\n"
85 " rdpr %%tick, %%g0"
86 :
87 : "r" (TICK_PRIV_BIT)
88 : "g2");
89}
90
91static void tick_disable_irq(void)
92{
93 __asm__ __volatile__(
94 " ba,pt %%xcc, 1f\n"
95 " nop\n"
96 " .align 64\n"
97 "1: wr %0, 0x0, %%tick_cmpr\n"
98 " rd %%tick_cmpr, %%g0"
99 :
100 : "r" (TICKCMP_IRQ_BIT));
101}
102
103static void tick_init_tick(void)
104{
105 tick_disable_protection();
106 tick_disable_irq();
107}
108
109static unsigned long long tick_get_tick(void)
110{
111 unsigned long ret;
112
113 __asm__ __volatile__("rd %%tick, %0\n\t"
114 "mov %0, %0"
115 : "=r" (ret));
116
117 return ret & ~TICK_PRIV_BIT;
118}
119
120static int tick_add_compare(unsigned long adj)
121{
122 unsigned long orig_tick, new_tick, new_compare;
123
124 __asm__ __volatile__("rd %%tick, %0"
125 : "=r" (orig_tick));
126
127 orig_tick &= ~TICKCMP_IRQ_BIT;
128
129
130
131
132
133
134
135
136
137
138 __asm__ __volatile__("ba,pt %%xcc, 1f\n\t"
139 " add %1, %2, %0\n\t"
140 ".align 64\n"
141 "1:\n\t"
142 "wr %0, 0, %%tick_cmpr\n\t"
143 "rd %%tick_cmpr, %%g0\n\t"
144 : "=r" (new_compare)
145 : "r" (orig_tick), "r" (adj));
146
147 __asm__ __volatile__("rd %%tick, %0"
148 : "=r" (new_tick));
149 new_tick &= ~TICKCMP_IRQ_BIT;
150
151 return ((long)(new_tick - (orig_tick+adj))) > 0L;
152}
153
154static unsigned long tick_add_tick(unsigned long adj)
155{
156 unsigned long new_tick;
157
158
159 __asm__ __volatile__("rd %%tick, %0\n\t"
160 "add %0, %1, %0\n\t"
161 "wrpr %0, 0, %%tick\n\t"
162 : "=&r" (new_tick)
163 : "r" (adj));
164
165 return new_tick;
166}
167
168static struct sparc64_tick_ops tick_operations __read_mostly = {
169 .name = "tick",
170 .init_tick = tick_init_tick,
171 .disable_irq = tick_disable_irq,
172 .get_tick = tick_get_tick,
173 .add_tick = tick_add_tick,
174 .add_compare = tick_add_compare,
175 .softint_mask = 1UL << 0,
176};
177
178struct sparc64_tick_ops *tick_ops __read_mostly = &tick_operations;
179EXPORT_SYMBOL(tick_ops);
180
181static void stick_disable_irq(void)
182{
183 __asm__ __volatile__(
184 "wr %0, 0x0, %%asr25"
185 :
186 : "r" (TICKCMP_IRQ_BIT));
187}
188
189static void stick_init_tick(void)
190{
191
192
193
194
195 if (tlb_type != hypervisor) {
196 tick_disable_protection();
197 tick_disable_irq();
198
199
200 __asm__ __volatile__(
201 " rd %%asr24, %%g2\n"
202 " andn %%g2, %0, %%g2\n"
203 " wr %%g2, 0, %%asr24"
204 :
205 : "r" (TICK_PRIV_BIT)
206 : "g1", "g2");
207 }
208
209 stick_disable_irq();
210}
211
212static unsigned long long stick_get_tick(void)
213{
214 unsigned long ret;
215
216 __asm__ __volatile__("rd %%asr24, %0"
217 : "=r" (ret));
218
219 return ret & ~TICK_PRIV_BIT;
220}
221
222static unsigned long stick_add_tick(unsigned long adj)
223{
224 unsigned long new_tick;
225
226 __asm__ __volatile__("rd %%asr24, %0\n\t"
227 "add %0, %1, %0\n\t"
228 "wr %0, 0, %%asr24\n\t"
229 : "=&r" (new_tick)
230 : "r" (adj));
231
232 return new_tick;
233}
234
235static int stick_add_compare(unsigned long adj)
236{
237 unsigned long orig_tick, new_tick;
238
239 __asm__ __volatile__("rd %%asr24, %0"
240 : "=r" (orig_tick));
241 orig_tick &= ~TICKCMP_IRQ_BIT;
242
243 __asm__ __volatile__("wr %0, 0, %%asr25"
244 :
245 : "r" (orig_tick + adj));
246
247 __asm__ __volatile__("rd %%asr24, %0"
248 : "=r" (new_tick));
249 new_tick &= ~TICKCMP_IRQ_BIT;
250
251 return ((long)(new_tick - (orig_tick+adj))) > 0L;
252}
253
254static struct sparc64_tick_ops stick_operations __read_mostly = {
255 .name = "stick",
256 .init_tick = stick_init_tick,
257 .disable_irq = stick_disable_irq,
258 .get_tick = stick_get_tick,
259 .add_tick = stick_add_tick,
260 .add_compare = stick_add_compare,
261 .softint_mask = 1UL << 16,
262};
263
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279
280
281#define HBIRD_STICKCMP_ADDR 0x1fe0000f060UL
282#define HBIRD_STICK_ADDR 0x1fe0000f070UL
283
284static unsigned long __hbird_read_stick(void)
285{
286 unsigned long ret, tmp1, tmp2, tmp3;
287 unsigned long addr = HBIRD_STICK_ADDR+8;
288
289 __asm__ __volatile__("ldxa [%1] %5, %2\n"
290 "1:\n\t"
291 "sub %1, 0x8, %1\n\t"
292 "ldxa [%1] %5, %3\n\t"
293 "add %1, 0x8, %1\n\t"
294 "ldxa [%1] %5, %4\n\t"
295 "cmp %4, %2\n\t"
296 "bne,a,pn %%xcc, 1b\n\t"
297 " mov %4, %2\n\t"
298 "sllx %4, 32, %4\n\t"
299 "or %3, %4, %0\n\t"
300 : "=&r" (ret), "=&r" (addr),
301 "=&r" (tmp1), "=&r" (tmp2), "=&r" (tmp3)
302 : "i" (ASI_PHYS_BYPASS_EC_E), "1" (addr));
303
304 return ret;
305}
306
307static void __hbird_write_stick(unsigned long val)
308{
309 unsigned long low = (val & 0xffffffffUL);
310 unsigned long high = (val >> 32UL);
311 unsigned long addr = HBIRD_STICK_ADDR;
312
313 __asm__ __volatile__("stxa %%g0, [%0] %4\n\t"
314 "add %0, 0x8, %0\n\t"
315 "stxa %3, [%0] %4\n\t"
316 "sub %0, 0x8, %0\n\t"
317 "stxa %2, [%0] %4"
318 : "=&r" (addr)
319 : "0" (addr), "r" (low), "r" (high),
320 "i" (ASI_PHYS_BYPASS_EC_E));
321}
322
323static void __hbird_write_compare(unsigned long val)
324{
325 unsigned long low = (val & 0xffffffffUL);
326 unsigned long high = (val >> 32UL);
327 unsigned long addr = HBIRD_STICKCMP_ADDR + 0x8UL;
328
329 __asm__ __volatile__("stxa %3, [%0] %4\n\t"
330 "sub %0, 0x8, %0\n\t"
331 "stxa %2, [%0] %4"
332 : "=&r" (addr)
333 : "0" (addr), "r" (low), "r" (high),
334 "i" (ASI_PHYS_BYPASS_EC_E));
335}
336
337static void hbtick_disable_irq(void)
338{
339 __hbird_write_compare(TICKCMP_IRQ_BIT);
340}
341
342static void hbtick_init_tick(void)
343{
344 tick_disable_protection();
345
346
347
348
349
350
351 __hbird_write_stick(__hbird_read_stick());
352
353 hbtick_disable_irq();
354}
355
356static unsigned long long hbtick_get_tick(void)
357{
358 return __hbird_read_stick() & ~TICK_PRIV_BIT;
359}
360
361static unsigned long hbtick_add_tick(unsigned long adj)
362{
363 unsigned long val;
364
365 val = __hbird_read_stick() + adj;
366 __hbird_write_stick(val);
367
368 return val;
369}
370
371static int hbtick_add_compare(unsigned long adj)
372{
373 unsigned long val = __hbird_read_stick();
374 unsigned long val2;
375
376 val &= ~TICKCMP_IRQ_BIT;
377 val += adj;
378 __hbird_write_compare(val);
379
380 val2 = __hbird_read_stick() & ~TICKCMP_IRQ_BIT;
381
382 return ((long)(val2 - val)) > 0L;
383}
384
385static struct sparc64_tick_ops hbtick_operations __read_mostly = {
386 .name = "hbtick",
387 .init_tick = hbtick_init_tick,
388 .disable_irq = hbtick_disable_irq,
389 .get_tick = hbtick_get_tick,
390 .add_tick = hbtick_add_tick,
391 .add_compare = hbtick_add_compare,
392 .softint_mask = 1UL << 0,
393};
394
395static unsigned long timer_ticks_per_nsec_quotient __read_mostly;
396
397int update_persistent_clock(struct timespec now)
398{
399 struct rtc_device *rtc = rtc_class_open("rtc0");
400 int err = -1;
401
402 if (rtc) {
403 err = rtc_set_mmss(rtc, now.tv_sec);
404 rtc_class_close(rtc);
405 }
406
407 return err;
408}
409
410unsigned long cmos_regs;
411EXPORT_SYMBOL(cmos_regs);
412
413static struct resource rtc_cmos_resource;
414
415static struct platform_device rtc_cmos_device = {
416 .name = "rtc_cmos",
417 .id = -1,
418 .resource = &rtc_cmos_resource,
419 .num_resources = 1,
420};
421
422static int __devinit rtc_probe(struct platform_device *op)
423{
424 struct resource *r;
425
426 printk(KERN_INFO "%s: RTC regs at 0x%llx\n",
427 op->dev.of_node->full_name, op->resource[0].start);
428
429
430
431
432
433
434
435 r = &rtc_cmos_resource;
436 r->flags = IORESOURCE_IO;
437 r->name = op->resource[0].name;
438 r->start = op->resource[0].start;
439 r->end = op->resource[0].end;
440
441 cmos_regs = op->resource[0].start;
442 return platform_device_register(&rtc_cmos_device);
443}
444
445static const struct of_device_id rtc_match[] = {
446 {
447 .name = "rtc",
448 .compatible = "m5819",
449 },
450 {
451 .name = "rtc",
452 .compatible = "isa-m5819p",
453 },
454 {
455 .name = "rtc",
456 .compatible = "isa-m5823p",
457 },
458 {
459 .name = "rtc",
460 .compatible = "ds1287",
461 },
462 {},
463};
464
465static struct platform_driver rtc_driver = {
466 .probe = rtc_probe,
467 .driver = {
468 .name = "rtc",
469 .owner = THIS_MODULE,
470 .of_match_table = rtc_match,
471 },
472};
473
474static struct platform_device rtc_bq4802_device = {
475 .name = "rtc-bq4802",
476 .id = -1,
477 .num_resources = 1,
478};
479
480static int __devinit bq4802_probe(struct platform_device *op)
481{
482
483 printk(KERN_INFO "%s: BQ4802 regs at 0x%llx\n",
484 op->dev.of_node->full_name, op->resource[0].start);
485
486 rtc_bq4802_device.resource = &op->resource[0];
487 return platform_device_register(&rtc_bq4802_device);
488}
489
490static const struct of_device_id bq4802_match[] = {
491 {
492 .name = "rtc",
493 .compatible = "bq4802",
494 },
495 {},
496};
497
498static struct platform_driver bq4802_driver = {
499 .probe = bq4802_probe,
500 .driver = {
501 .name = "bq4802",
502 .owner = THIS_MODULE,
503 .of_match_table = bq4802_match,
504 },
505};
506
507static unsigned char mostek_read_byte(struct device *dev, u32 ofs)
508{
509 struct platform_device *pdev = to_platform_device(dev);
510 void __iomem *regs = (void __iomem *) pdev->resource[0].start;
511
512 return readb(regs + ofs);
513}
514
515static void mostek_write_byte(struct device *dev, u32 ofs, u8 val)
516{
517 struct platform_device *pdev = to_platform_device(dev);
518 void __iomem *regs = (void __iomem *) pdev->resource[0].start;
519
520 writeb(val, regs + ofs);
521}
522
523static struct m48t59_plat_data m48t59_data = {
524 .read_byte = mostek_read_byte,
525 .write_byte = mostek_write_byte,
526};
527
528static struct platform_device m48t59_rtc = {
529 .name = "rtc-m48t59",
530 .id = 0,
531 .num_resources = 1,
532 .dev = {
533 .platform_data = &m48t59_data,
534 },
535};
536
537static int __devinit mostek_probe(struct platform_device *op)
538{
539 struct device_node *dp = op->dev.of_node;
540
541
542
543
544 if (!strcmp(dp->parent->name, "fhc") &&
545 strcmp(dp->parent->parent->name, "central") != 0)
546 return -ENODEV;
547
548 printk(KERN_INFO "%s: Mostek regs at 0x%llx\n",
549 dp->full_name, op->resource[0].start);
550
551 m48t59_rtc.resource = &op->resource[0];
552 return platform_device_register(&m48t59_rtc);
553}
554
555static const struct of_device_id mostek_match[] = {
556 {
557 .name = "eeprom",
558 },
559 {},
560};
561
562static struct platform_driver mostek_driver = {
563 .probe = mostek_probe,
564 .driver = {
565 .name = "mostek",
566 .owner = THIS_MODULE,
567 .of_match_table = mostek_match,
568 },
569};
570
571static struct platform_device rtc_sun4v_device = {
572 .name = "rtc-sun4v",
573 .id = -1,
574};
575
576static struct platform_device rtc_starfire_device = {
577 .name = "rtc-starfire",
578 .id = -1,
579};
580
581static int __init clock_init(void)
582{
583 if (this_is_starfire)
584 return platform_device_register(&rtc_starfire_device);
585
586 if (tlb_type == hypervisor)
587 return platform_device_register(&rtc_sun4v_device);
588
589 (void) platform_driver_register(&rtc_driver);
590 (void) platform_driver_register(&mostek_driver);
591 (void) platform_driver_register(&bq4802_driver);
592
593 return 0;
594}
595
596
597
598
599
600fs_initcall(clock_init);
601
602
603static unsigned long sparc64_init_timers(void)
604{
605 struct device_node *dp;
606 unsigned long freq;
607
608 dp = of_find_node_by_path("/");
609 if (tlb_type == spitfire) {
610 unsigned long ver, manuf, impl;
611
612 __asm__ __volatile__ ("rdpr %%ver, %0"
613 : "=&r" (ver));
614 manuf = ((ver >> 48) & 0xffff);
615 impl = ((ver >> 32) & 0xffff);
616 if (manuf == 0x17 && impl == 0x13) {
617
618 tick_ops = &hbtick_operations;
619 freq = of_getintprop_default(dp, "stick-frequency", 0);
620 } else {
621 tick_ops = &tick_operations;
622 freq = local_cpu_data().clock_tick;
623 }
624 } else {
625 tick_ops = &stick_operations;
626 freq = of_getintprop_default(dp, "stick-frequency", 0);
627 }
628
629 return freq;
630}
631
632struct freq_table {
633 unsigned long clock_tick_ref;
634 unsigned int ref_freq;
635};
636static DEFINE_PER_CPU(struct freq_table, sparc64_freq_table) = { 0, 0 };
637
638unsigned long sparc64_get_clock_tick(unsigned int cpu)
639{
640 struct freq_table *ft = &per_cpu(sparc64_freq_table, cpu);
641
642 if (ft->clock_tick_ref)
643 return ft->clock_tick_ref;
644 return cpu_data(cpu).clock_tick;
645}
646EXPORT_SYMBOL(sparc64_get_clock_tick);
647
648#ifdef CONFIG_CPU_FREQ
649
650static int sparc64_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
651 void *data)
652{
653 struct cpufreq_freqs *freq = data;
654 unsigned int cpu = freq->cpu;
655 struct freq_table *ft = &per_cpu(sparc64_freq_table, cpu);
656
657 if (!ft->ref_freq) {
658 ft->ref_freq = freq->old;
659 ft->clock_tick_ref = cpu_data(cpu).clock_tick;
660 }
661 if ((val == CPUFREQ_PRECHANGE && freq->old < freq->new) ||
662 (val == CPUFREQ_POSTCHANGE && freq->old > freq->new) ||
663 (val == CPUFREQ_RESUMECHANGE)) {
664 cpu_data(cpu).clock_tick =
665 cpufreq_scale(ft->clock_tick_ref,
666 ft->ref_freq,
667 freq->new);
668 }
669
670 return 0;
671}
672
673static struct notifier_block sparc64_cpufreq_notifier_block = {
674 .notifier_call = sparc64_cpufreq_notifier
675};
676
677static int __init register_sparc64_cpufreq_notifier(void)
678{
679
680 cpufreq_register_notifier(&sparc64_cpufreq_notifier_block,
681 CPUFREQ_TRANSITION_NOTIFIER);
682 return 0;
683}
684
685core_initcall(register_sparc64_cpufreq_notifier);
686
687#endif
688
689static int sparc64_next_event(unsigned long delta,
690 struct clock_event_device *evt)
691{
692 return tick_ops->add_compare(delta) ? -ETIME : 0;
693}
694
695static void sparc64_timer_setup(enum clock_event_mode mode,
696 struct clock_event_device *evt)
697{
698 switch (mode) {
699 case CLOCK_EVT_MODE_ONESHOT:
700 case CLOCK_EVT_MODE_RESUME:
701 break;
702
703 case CLOCK_EVT_MODE_SHUTDOWN:
704 tick_ops->disable_irq();
705 break;
706
707 case CLOCK_EVT_MODE_PERIODIC:
708 case CLOCK_EVT_MODE_UNUSED:
709 WARN_ON(1);
710 break;
711 }
712}
713
714static struct clock_event_device sparc64_clockevent = {
715 .features = CLOCK_EVT_FEAT_ONESHOT,
716 .set_mode = sparc64_timer_setup,
717 .set_next_event = sparc64_next_event,
718 .rating = 100,
719 .shift = 30,
720 .irq = -1,
721};
722static DEFINE_PER_CPU(struct clock_event_device, sparc64_events);
723
724void __irq_entry timer_interrupt(int irq, struct pt_regs *regs)
725{
726 struct pt_regs *old_regs = set_irq_regs(regs);
727 unsigned long tick_mask = tick_ops->softint_mask;
728 int cpu = smp_processor_id();
729 struct clock_event_device *evt = &per_cpu(sparc64_events, cpu);
730
731 clear_softint(tick_mask);
732
733 irq_enter();
734
735 local_cpu_data().irq0_irqs++;
736 kstat_incr_irqs_this_cpu(0, irq_to_desc(0));
737
738 if (unlikely(!evt->event_handler)) {
739 printk(KERN_WARNING
740 "Spurious SPARC64 timer interrupt on cpu %d\n", cpu);
741 } else
742 evt->event_handler(evt);
743
744 irq_exit();
745
746 set_irq_regs(old_regs);
747}
748
749void __devinit setup_sparc64_timer(void)
750{
751 struct clock_event_device *sevt;
752 unsigned long pstate;
753
754
755
756
757 __asm__ __volatile__("rdpr %%pstate, %0\n\t"
758 "wrpr %0, %1, %%pstate"
759 : "=r" (pstate)
760 : "i" (PSTATE_IE));
761
762 tick_ops->init_tick();
763
764
765 __asm__ __volatile__("wrpr %0, 0x0, %%pstate"
766 :
767 : "r" (pstate));
768
769 sevt = &__get_cpu_var(sparc64_events);
770
771 memcpy(sevt, &sparc64_clockevent, sizeof(*sevt));
772 sevt->cpumask = cpumask_of(smp_processor_id());
773
774 clockevents_register_device(sevt);
775}
776
777#define SPARC64_NSEC_PER_CYC_SHIFT 10UL
778
779static struct clocksource clocksource_tick = {
780 .rating = 100,
781 .mask = CLOCKSOURCE_MASK(64),
782 .flags = CLOCK_SOURCE_IS_CONTINUOUS,
783};
784
785static unsigned long tb_ticks_per_usec __read_mostly;
786
787void __delay(unsigned long loops)
788{
789 unsigned long bclock, now;
790
791 bclock = tick_ops->get_tick();
792 do {
793 now = tick_ops->get_tick();
794 } while ((now-bclock) < loops);
795}
796EXPORT_SYMBOL(__delay);
797
798void udelay(unsigned long usecs)
799{
800 __delay(tb_ticks_per_usec * usecs);
801}
802EXPORT_SYMBOL(udelay);
803
804static cycle_t clocksource_tick_read(struct clocksource *cs)
805{
806 return tick_ops->get_tick();
807}
808
809void __init time_init(void)
810{
811 unsigned long freq = sparc64_init_timers();
812
813 tb_ticks_per_usec = freq / USEC_PER_SEC;
814
815 timer_ticks_per_nsec_quotient =
816 clocksource_hz2mult(freq, SPARC64_NSEC_PER_CYC_SHIFT);
817
818 clocksource_tick.name = tick_ops->name;
819 clocksource_tick.read = clocksource_tick_read;
820
821 clocksource_register_hz(&clocksource_tick, freq);
822 printk("clocksource: mult[%x] shift[%d]\n",
823 clocksource_tick.mult, clocksource_tick.shift);
824
825 sparc64_clockevent.name = tick_ops->name;
826 clockevents_calc_mult_shift(&sparc64_clockevent, freq, 4);
827
828 sparc64_clockevent.max_delta_ns =
829 clockevent_delta2ns(0x7fffffffffffffffUL, &sparc64_clockevent);
830 sparc64_clockevent.min_delta_ns =
831 clockevent_delta2ns(0xF, &sparc64_clockevent);
832
833 printk("clockevent: mult[%x] shift[%d]\n",
834 sparc64_clockevent.mult, sparc64_clockevent.shift);
835
836 setup_sparc64_timer();
837}
838
839unsigned long long sched_clock(void)
840{
841 unsigned long ticks = tick_ops->get_tick();
842
843 return (ticks * timer_ticks_per_nsec_quotient)
844 >> SPARC64_NSEC_PER_CYC_SHIFT;
845}
846
847int __devinit read_current_timer(unsigned long *timer_val)
848{
849 *timer_val = tick_ops->get_tick();
850 return 0;
851}
852