1/* calibrate.c: default delay calibration
2 *
3 * Excised from init/main.c
4 *  Copyright (C) 1991, 1992  Linus Torvalds
5 */
6
7#include <linux/jiffies.h>
8#include <linux/delay.h>
9#include <linux/init.h>
10#include <linux/timex.h>
11#include <linux/smp.h>
12#include <linux/percpu.h>
13
14unsigned long lpj_fine;
15unsigned long preset_lpj;
16static int __init lpj_setup(char *str)
17{
18	preset_lpj = simple_strtoul(str,NULL,0);
19	return 1;
20}
21
22__setup("lpj=", lpj_setup);
23
24#ifdef ARCH_HAS_READ_CURRENT_TIMER
25
26/* This routine uses the read_current_timer() routine and gets the
27 * loops per jiffy directly, instead of guessing it using delay().
28 * Also, this code tries to handle non-maskable asynchronous events
29 * (like SMIs)
30 */
31#define DELAY_CALIBRATION_TICKS			((HZ < 100) ? 1 : (HZ/100))
32#define MAX_DIRECT_CALIBRATION_RETRIES		5
33
34static unsigned long calibrate_delay_direct(void)
35{
36	unsigned long pre_start, start, post_start;
37	unsigned long pre_end, end, post_end;
38	unsigned long start_jiffies;
39	unsigned long timer_rate_min, timer_rate_max;
40	unsigned long good_timer_sum = 0;
41	unsigned long good_timer_count = 0;
42	unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
43	int max = -1; /* index of measured_times with max/min values or not set */
44	int min = -1;
45	int i;
46
47	if (read_current_timer(&pre_start) < 0 )
48		return 0;
49
50	/*
51	 * A simple loop like
52	 *	while ( jiffies < start_jiffies+1)
53	 *		start = read_current_timer();
54	 * will not do. As we don't really know whether jiffy switch
55	 * happened first or timer_value was read first. And some asynchronous
56	 * event can happen between these two events introducing errors in lpj.
57	 *
58	 * So, we do
59	 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
60	 * 2. check jiffy switch
61	 * 3. start <- timer value before or after jiffy switch
62	 * 4. post_start <- When we are sure that jiffy switch has happened
63	 *
64	 * Note, we don't know anything about order of 2 and 3.
65	 * Now, by looking at post_start and pre_start difference, we can
66	 * check whether any asynchronous event happened or not
67	 */
68
69	for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
70		pre_start = 0;
71		read_current_timer(&start);
72		start_jiffies = jiffies;
73		while (time_before_eq(jiffies, start_jiffies + 1)) {
74			pre_start = start;
75			read_current_timer(&start);
76		}
77		read_current_timer(&post_start);
78
79		pre_end = 0;
80		end = post_start;
81		while (time_before_eq(jiffies, start_jiffies + 1 +
82					       DELAY_CALIBRATION_TICKS)) {
83			pre_end = end;
84			read_current_timer(&end);
85		}
86		read_current_timer(&post_end);
87
88		timer_rate_max = (post_end - pre_start) /
89					DELAY_CALIBRATION_TICKS;
90		timer_rate_min = (pre_end - post_start) /
91					DELAY_CALIBRATION_TICKS;
92
93		/*
94		 * If the upper limit and lower limit of the timer_rate is
95		 * >= 12.5% apart, redo calibration.
96		 */
97		if (start >= post_end)
98			printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
99					"timer_rate as we had a TSC wrap around"
100					" start=%lu >=post_end=%lu\n",
101				start, post_end);
102		if (start < post_end && pre_start != 0 && pre_end != 0 &&
103		    (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
104			good_timer_count++;
105			good_timer_sum += timer_rate_max;
106			measured_times[i] = timer_rate_max;
107			if (max < 0 || timer_rate_max > measured_times[max])
108				max = i;
109			if (min < 0 || timer_rate_max < measured_times[min])
110				min = i;
111		} else
112			measured_times[i] = 0;
113
114	}
115
116	/*
117	 * Find the maximum & minimum - if they differ too much throw out the
118	 * one with the largest difference from the mean and try again...
119	 */
120	while (good_timer_count > 1) {
121		unsigned long estimate;
122		unsigned long maxdiff;
123
124		/* compute the estimate */
125		estimate = (good_timer_sum/good_timer_count);
126		maxdiff = estimate >> 3;
127
128		/* if range is within 12% let's take it */
129		if ((measured_times[max] - measured_times[min]) < maxdiff)
130			return estimate;
131
132		/* ok - drop the worse value and try again... */
133		good_timer_sum = 0;
134		good_timer_count = 0;
135		if ((measured_times[max] - estimate) <
136				(estimate - measured_times[min])) {
137			printk(KERN_NOTICE "calibrate_delay_direct() dropping "
138					"min bogoMips estimate %d = %lu\n",
139				min, measured_times[min]);
140			measured_times[min] = 0;
141			min = max;
142		} else {
143			printk(KERN_NOTICE "calibrate_delay_direct() dropping "
144					"max bogoMips estimate %d = %lu\n",
145				max, measured_times[max]);
146			measured_times[max] = 0;
147			max = min;
148		}
149
150		for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
151			if (measured_times[i] == 0)
152				continue;
153			good_timer_count++;
154			good_timer_sum += measured_times[i];
155			if (measured_times[i] < measured_times[min])
156				min = i;
157			if (measured_times[i] > measured_times[max])
158				max = i;
159		}
160
161	}
162
163	printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
164	       "estimate for loops_per_jiffy.\nProbably due to long platform "
165		"interrupts. Consider using \"lpj=\" boot option.\n");
166	return 0;
167}
168#else
169static unsigned long calibrate_delay_direct(void)
170{
171	return 0;
172}
173#endif
174
175/*
176 * This is the number of bits of precision for the loops_per_jiffy.  Each
177 * time we refine our estimate after the first takes 1.5/HZ seconds, so try
178 * to start with a good estimate.
179 * For the boot cpu we can skip the delay calibration and assign it a value
180 * calculated based on the timer frequency.
181 * For the rest of the CPUs we cannot assume that the timer frequency is same as
182 * the cpu frequency, hence do the calibration for those.
183 */
184#define LPS_PREC 8
185
186static unsigned long calibrate_delay_converge(void)
187{
188	/* First stage - slowly accelerate to find initial bounds */
189	unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
190	int trials = 0, band = 0, trial_in_band = 0;
191
192	lpj = (1<<12);
193
194	/* wait for "start of" clock tick */
195	ticks = jiffies;
196	while (ticks == jiffies)
197		; /* nothing */
198	/* Go .. */
199	ticks = jiffies;
200	do {
201		if (++trial_in_band == (1<<band)) {
202			++band;
203			trial_in_band = 0;
204		}
205		__delay(lpj * band);
206		trials += band;
207	} while (ticks == jiffies);
208	/*
209	 * We overshot, so retreat to a clear underestimate. Then estimate
210	 * the largest likely undershoot. This defines our chop bounds.
211	 */
212	trials -= band;
213	loopadd_base = lpj * band;
214	lpj_base = lpj * trials;
215
216recalibrate:
217	lpj = lpj_base;
218	loopadd = loopadd_base;
219
220	/*
221	 * Do a binary approximation to get lpj set to
222	 * equal one clock (up to LPS_PREC bits)
223	 */
224	chop_limit = lpj >> LPS_PREC;
225	while (loopadd > chop_limit) {
226		lpj += loopadd;
227		ticks = jiffies;
228		while (ticks == jiffies)
229			; /* nothing */
230		ticks = jiffies;
231		__delay(lpj);
232		if (jiffies != ticks)	/* longer than 1 tick */
233			lpj -= loopadd;
234		loopadd >>= 1;
235	}
236	/*
237	 * If we incremented every single time possible, presume we've
238	 * massively underestimated initially, and retry with a higher
239	 * start, and larger range. (Only seen on x86_64, due to SMIs)
240	 */
241	if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
242		lpj_base = lpj;
243		loopadd_base <<= 2;
244		goto recalibrate;
245	}
246
247	return lpj;
248}
249
250static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
251
252/*
253 * Check if cpu calibration delay is already known. For example,
254 * some processors with multi-core sockets may have all cores
255 * with the same calibration delay.
256 *
257 * Architectures should override this function if a faster calibration
258 * method is available.
259 */
260unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
261{
262	return 0;
263}
264
265/*
266 * Indicate the cpu delay calibration is done. This can be used by
267 * architectures to stop accepting delay timer registrations after this point.
268 */
269
270void __attribute__((weak)) calibration_delay_done(void)
271{
272}
273
274void calibrate_delay(void)
275{
276	unsigned long lpj;
277	static bool printed;
278	int this_cpu = smp_processor_id();
279
280	if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
281		lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
282		if (!printed)
283			pr_info("Calibrating delay loop (skipped) "
284				"already calibrated this CPU");
285	} else if (preset_lpj) {
286		lpj = preset_lpj;
287		if (!printed)
288			pr_info("Calibrating delay loop (skipped) "
289				"preset value.. ");
290	} else if ((!printed) && lpj_fine) {
291		lpj = lpj_fine;
292		pr_info("Calibrating delay loop (skipped), "
293			"value calculated using timer frequency.. ");
294	} else if ((lpj = calibrate_delay_is_known())) {
295		;
296	} else if ((lpj = calibrate_delay_direct()) != 0) {
297		if (!printed)
298			pr_info("Calibrating delay using timer "
299				"specific routine.. ");
300	} else {
301		if (!printed)
302			pr_info("Calibrating delay loop... ");
303		lpj = calibrate_delay_converge();
304	}
305	per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
306	if (!printed)
307		pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
308			lpj/(500000/HZ),
309			(lpj/(5000/HZ)) % 100, lpj);
310
311	loops_per_jiffy = lpj;
312	printed = true;
313
314	calibration_delay_done();
315}
316