aboutsummaryrefslogtreecommitdiffstats
path: root/arch/parisc/kernel/time.c
blob: bad7d1eb62b975dff89921860ca30e816e948de3 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
/*
 *  linux/arch/parisc/kernel/time.c
 *
 *  Copyright (C) 1991, 1992, 1995  Linus Torvalds
 *  Modifications for ARM (C) 1994, 1995, 1996,1997 Russell King
 *  Copyright (C) 1999 SuSE GmbH, (Philipp Rumpf, prumpf@tux.org)
 *
 * 1994-07-02  Alan Modra
 *             fixed set_rtc_mmss, fixed time.year for >= 2000, new mktime
 * 1998-12-20  Updated NTP code according to technical memorandum Jan '96
 *             "A Kernel Model for Precision Timekeeping" by Dave Mills
 */
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/param.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/interrupt.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/profile.h>

#include <asm/uaccess.h>
#include <asm/io.h>
#include <asm/irq.h>
#include <asm/param.h>
#include <asm/pdc.h>
#include <asm/led.h>

#include <linux/timex.h>

static unsigned long clocktick __read_mostly;	/* timer cycles per tick */

/*
 * We keep time on PA-RISC Linux by using the Interval Timer which is
 * a pair of registers; one is read-only and one is write-only; both
 * accessed through CR16.  The read-only register is 32 or 64 bits wide,
 * and increments by 1 every CPU clock tick.  The architecture only
 * guarantees us a rate between 0.5 and 2, but all implementations use a
 * rate of 1.  The write-only register is 32-bits wide.  When the lowest
 * 32 bits of the read-only register compare equal to the write-only
 * register, it raises a maskable external interrupt.  Each processor has
 * an Interval Timer of its own and they are not synchronised.  
 *
 * We want to generate an interrupt every 1/HZ seconds.  So we program
 * CR16 to interrupt every @clocktick cycles.  The it_value in cpu_data
 * is programmed with the intended time of the next tick.  We can be
 * held off for an arbitrarily long period of time by interrupts being
 * disabled, so we may miss one or more ticks.
 */
irqreturn_t timer_interrupt(int irq, void *dev_id)
{
	unsigned long now;
	unsigned long next_tick;
	unsigned long cycles_elapsed, ticks_elapsed;
	unsigned long cycles_remainder;
	unsigned int cpu = smp_processor_id();
	struct cpuinfo_parisc *cpuinfo = &cpu_data[cpu];

	/* gcc can optimize for "read-only" case with a local clocktick */
	unsigned long cpt = clocktick;

	profile_tick(CPU_PROFILING);

	/* Initialize next_tick to the expected tick time. */
	next_tick = cpuinfo->it_value;

	/* Get current interval timer.
	 * CR16 reads as 64 bits in CPU wide mode.
	 * CR16 reads as 32 bits in CPU narrow mode.
	 */
	now = mfctl(16);

	cycles_elapsed = now - next_tick;

	if ((cycles_elapsed >> 5) < cpt) {
		/* use "cheap" math (add/subtract) instead
		 * of the more expensive div/mul method
		 */
		cycles_remainder = cycles_elapsed;
		ticks_elapsed = 1;
		while (cycles_remainder > cpt) {
			cycles_remainder -= cpt;
			ticks_elapsed++;
		}
	} else {
		cycles_remainder = cycles_elapsed % cpt;
		ticks_elapsed = 1 + cycles_elapsed / cpt;
	}

	/* Can we differentiate between "early CR16" (aka Scenario 1) and
	 * "long delay" (aka Scenario 3)? I don't think so.
	 *
	 * We expected timer_interrupt to be delivered at least a few hundred
	 * cycles after the IT fires. But it's arbitrary how much time passes
	 * before we call it "late". I've picked one second.
	 */
	if (ticks_elapsed > HZ) {
		/* Scenario 3: very long delay?  bad in any case */
		printk (KERN_CRIT "timer_interrupt(CPU %d): delayed!"
			" cycles %lX rem %lX "
			" next/now %lX/%lX\n",
			cpu,
			cycles_elapsed, cycles_remainder,
			next_tick, now );
	}

	/* convert from "division remainder" to "remainder of clock tick" */
	cycles_remainder = cpt - cycles_remainder;

	/* Determine when (in CR16 cycles) next IT interrupt will fire.
	 * We want IT to fire modulo clocktick even if we miss/skip some.
	 * But those interrupts don't in fact get delivered that regularly.
	 */
	next_tick = now + cycles_remainder;

	cpuinfo->it_value = next_tick;

	/* Skip one clocktick on purpose if we are likely to miss next_tick.
	 * We want to avoid the new next_tick being less than CR16.
	 * If that happened, itimer wouldn't fire until CR16 wrapped.
	 * We'll catch the tick we missed on the tick after that.
	 */
	if (!(cycles_remainder >> 13))
		next_tick += cpt;

	/* Program the IT when to deliver the next interrupt. */
	/* Only bottom 32-bits of next_tick are written to cr16.  */
	mtctl(next_tick, 16);


	/* Done mucking with unreliable delivery of interrupts.
	 * Go do system house keeping.
	 */

	if (!--cpuinfo->prof_counter) {
		cpuinfo->prof_counter = cpuinfo->prof_multiplier;
		update_process_times(user_mode(get_irq_regs()));
	}

	if (cpu == 0) {
		write_seqlock(&xtime_lock);
		do_timer(ticks_elapsed);
		write_sequnlock(&xtime_lock);
	}

	/* check soft power switch status */
	if (cpu == 0 && !atomic_read(&power_tasklet.count))
		tasklet_schedule(&power_tasklet);

	return IRQ_HANDLED;
}


unsigned long profile_pc(struct pt_regs *regs)
{
	unsigned long pc = instruction_pointer(regs);

	if (regs->gr[0] & PSW_N)
		pc -= 4;

#ifdef CONFIG_SMP
	if (in_lock_functions(pc))
		pc = regs->gr[2];
#endif

	return pc;
}
EXPORT_SYMBOL(profile_pc);


/*
 * Return the number of micro-seconds that elapsed since the last
 * update to wall time (aka xtime).  The xtime_lock
 * must be at least read-locked when calling this routine.
 */
static inline unsigned long gettimeoffset (void)
{
#ifndef CONFIG_SMP
	/*
	 * FIXME: This won't work on smp because jiffies are updated by cpu 0.
	 *    Once parisc-linux learns the cr16 difference between processors,
	 *    this could be made to work.
	 */
	unsigned long now;
	unsigned long prev_tick;
	unsigned long next_tick;
	unsigned long elapsed_cycles;
	unsigned long usec;
	unsigned long cpuid = smp_processor_id();
	unsigned long cpt = clocktick;

	next_tick = cpu_data[cpuid].it_value;
	now = mfctl(16);	/* Read the hardware interval timer.  */

	prev_tick = next_tick - cpt;

	/* Assume Scenario 1: "now" is later than prev_tick.  */
	elapsed_cycles = now - prev_tick;

/* aproximate HZ with shifts. Intended math is "(elapsed/clocktick) > HZ" */
#if HZ == 1000
	if (elapsed_cycles > (cpt << 10) )
#elif HZ == 250
	if (elapsed_cycles > (cpt << 8) )
#elif HZ == 100
	if (elapsed_cycles > (cpt << 7) )
#else
#warn WTF is HZ set to anyway?
	if (elapsed_cycles > (HZ * cpt) )
#endif
	{
		/* Scenario 3: clock ticks are missing. */
		printk (KERN_CRIT "gettimeoffset(CPU %ld): missing %ld ticks!"
			" cycles %lX prev/now/next %lX/%lX/%lX  clock %lX\n",
			cpuid, elapsed_cycles / cpt,
			elapsed_cycles, prev_tick, now, next_tick, cpt);
	}

	/* FIXME: Can we improve the precision? Not with PAGE0. */
	usec = (elapsed_cycles * 10000) / PAGE0->mem_10msec;
	return usec;
#else
	return 0;
#endif
}

void
do_gettimeofday (struct timeval *tv)
{
	unsigned long flags, seq, usec, sec;

	/* Hold xtime_lock and adjust timeval.  */
	do {
		seq = read_seqbegin_irqsave(&xtime_lock, flags);
		usec = gettimeoffset();
		sec = xtime.tv_sec;
		usec += (xtime.tv_nsec / 1000);
	} while (read_seqretry_irqrestore(&xtime_lock, seq, flags));

	/* Move adjusted usec's into sec's.  */
	while (usec >= USEC_PER_SEC) {
		usec -= USEC_PER_SEC;
		++sec;
	}

	/* Return adjusted result.  */
	tv->tv_sec = sec;
	tv->tv_usec = usec;
}

EXPORT_SYMBOL(do_gettimeofday);

int
do_settimeofday (struct timespec *tv)
{
	time_t wtm_sec, sec = tv->tv_sec;
	long wtm_nsec, nsec = tv->tv_nsec;

	if ((unsigned long)tv->tv_nsec >= NSEC_PER_SEC)
		return -EINVAL;

	write_seqlock_irq(&xtime_lock);
	{
		/*
		 * This is revolting. We need to set "xtime"
		 * correctly. However, the value in this location is
		 * the value at the most recent update of wall time.
		 * Discover what correction gettimeofday would have
		 * done, and then undo it!
		 */
		nsec -= gettimeoffset() * 1000;

		wtm_sec  = wall_to_monotonic.tv_sec + (xtime.tv_sec - sec);
		wtm_nsec = wall_to_monotonic.tv_nsec + (xtime.tv_nsec - nsec);

		set_normalized_timespec(&xtime, sec, nsec);
		set_normalized_timespec(&wall_to_monotonic, wtm_sec, wtm_nsec);

		ntp_clear();
	}
	write_sequnlock_irq(&xtime_lock);
	clock_was_set();
	return 0;
}
EXPORT_SYMBOL(do_settimeofday);

/*
 * XXX: We can do better than this.
 * Returns nanoseconds
 */

unsigned long long sched_clock(void)
{
	return (unsigned long long)jiffies * (1000000000 / HZ);
}


void __init start_cpu_itimer(void)
{
	unsigned int cpu = smp_processor_id();
	unsigned long next_tick = mfctl(16) + clocktick;

	mtctl(next_tick, 16);		/* kick off Interval Timer (CR16) */

	cpu_data[cpu].it_value = next_tick;
}

void __init time_init(void)
{
	static struct pdc_tod tod_data;

	clocktick = (100 * PAGE0->mem_10msec) / HZ;

	start_cpu_itimer();	/* get CPU 0 started */

	if (pdc_tod_read(&tod_data) == 0) {
		unsigned long flags;

		write_seqlock_irqsave(&xtime_lock, flags);
		xtime.tv_sec = tod_data.tod_sec;
		xtime.tv_nsec = tod_data.tod_usec * 1000;
		set_normalized_timespec(&wall_to_monotonic,
		                        -xtime.tv_sec, -xtime.tv_nsec);
		write_sequnlock_irqrestore(&xtime_lock, flags);
	} else {
		printk(KERN_ERR "Error reading tod clock\n");
	        xtime.tv_sec = 0;
		xtime.tv_nsec = 0;
	}
}