Merge branch 'btrfs-3.0' of git://github.com/chrismason/linux
[platform/adaptation/renesas_rcar/renesas_kernel.git] / init / calibrate.c
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
14 unsigned long lpj_fine;
15 unsigned long preset_lpj;
16 static 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
34 static unsigned long __cpuinit 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
169 static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
170 #endif
171
172 /*
173  * This is the number of bits of precision for the loops_per_jiffy.  Each
174  * time we refine our estimate after the first takes 1.5/HZ seconds, so try
175  * to start with a good estimate.
176  * For the boot cpu we can skip the delay calibration and assign it a value
177  * calculated based on the timer frequency.
178  * For the rest of the CPUs we cannot assume that the timer frequency is same as
179  * the cpu frequency, hence do the calibration for those.
180  */
181 #define LPS_PREC 8
182
183 static unsigned long __cpuinit calibrate_delay_converge(void)
184 {
185         /* First stage - slowly accelerate to find initial bounds */
186         unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
187         int trials = 0, band = 0, trial_in_band = 0;
188
189         lpj = (1<<12);
190
191         /* wait for "start of" clock tick */
192         ticks = jiffies;
193         while (ticks == jiffies)
194                 ; /* nothing */
195         /* Go .. */
196         ticks = jiffies;
197         do {
198                 if (++trial_in_band == (1<<band)) {
199                         ++band;
200                         trial_in_band = 0;
201                 }
202                 __delay(lpj * band);
203                 trials += band;
204         } while (ticks == jiffies);
205         /*
206          * We overshot, so retreat to a clear underestimate. Then estimate
207          * the largest likely undershoot. This defines our chop bounds.
208          */
209         trials -= band;
210         loopadd_base = lpj * band;
211         lpj_base = lpj * trials;
212
213 recalibrate:
214         lpj = lpj_base;
215         loopadd = loopadd_base;
216
217         /*
218          * Do a binary approximation to get lpj set to
219          * equal one clock (up to LPS_PREC bits)
220          */
221         chop_limit = lpj >> LPS_PREC;
222         while (loopadd > chop_limit) {
223                 lpj += loopadd;
224                 ticks = jiffies;
225                 while (ticks == jiffies)
226                         ; /* nothing */
227                 ticks = jiffies;
228                 __delay(lpj);
229                 if (jiffies != ticks)   /* longer than 1 tick */
230                         lpj -= loopadd;
231                 loopadd >>= 1;
232         }
233         /*
234          * If we incremented every single time possible, presume we've
235          * massively underestimated initially, and retry with a higher
236          * start, and larger range. (Only seen on x86_64, due to SMIs)
237          */
238         if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
239                 lpj_base = lpj;
240                 loopadd_base <<= 2;
241                 goto recalibrate;
242         }
243
244         return lpj;
245 }
246
247 static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
248
249 void __cpuinit calibrate_delay(void)
250 {
251         unsigned long lpj;
252         static bool printed;
253         int this_cpu = smp_processor_id();
254
255         if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
256                 lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
257                 pr_info("Calibrating delay loop (skipped) "
258                                 "already calibrated this CPU");
259         } else if (preset_lpj) {
260                 lpj = preset_lpj;
261                 if (!printed)
262                         pr_info("Calibrating delay loop (skipped) "
263                                 "preset value.. ");
264         } else if ((!printed) && lpj_fine) {
265                 lpj = lpj_fine;
266                 pr_info("Calibrating delay loop (skipped), "
267                         "value calculated using timer frequency.. ");
268         } else if ((lpj = calibrate_delay_direct()) != 0) {
269                 if (!printed)
270                         pr_info("Calibrating delay using timer "
271                                 "specific routine.. ");
272         } else {
273                 if (!printed)
274                         pr_info("Calibrating delay loop... ");
275                 lpj = calibrate_delay_converge();
276         }
277         per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
278         if (!printed)
279                 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
280                         lpj/(500000/HZ),
281                         (lpj/(5000/HZ)) % 100, lpj);
282
283         loops_per_jiffy = lpj;
284         printed = true;
285 }