1 // SPDX-License-Identifier: GPL-2.0 <<
2 /* calibrate.c: default delay calibration 1 /* calibrate.c: default delay calibration
3 * 2 *
4 * Excised from init/main.c 3 * Excised from init/main.c
5 * Copyright (C) 1991, 1992 Linus Torvalds 4 * Copyright (C) 1991, 1992 Linus Torvalds
6 */ 5 */
7 6
8 #include <linux/jiffies.h> 7 #include <linux/jiffies.h>
9 #include <linux/delay.h> 8 #include <linux/delay.h>
10 #include <linux/init.h> 9 #include <linux/init.h>
11 #include <linux/timex.h> 10 #include <linux/timex.h>
12 #include <linux/smp.h> 11 #include <linux/smp.h>
13 #include <linux/percpu.h> <<
14 12
15 unsigned long lpj_fine; 13 unsigned long lpj_fine;
16 unsigned long preset_lpj; 14 unsigned long preset_lpj;
17 static int __init lpj_setup(char *str) 15 static int __init lpj_setup(char *str)
18 { 16 {
19 preset_lpj = simple_strtoul(str,NULL,0 17 preset_lpj = simple_strtoul(str,NULL,0);
20 return 1; 18 return 1;
21 } 19 }
22 20
23 __setup("lpj=", lpj_setup); 21 __setup("lpj=", lpj_setup);
24 22
25 #ifdef ARCH_HAS_READ_CURRENT_TIMER 23 #ifdef ARCH_HAS_READ_CURRENT_TIMER
26 24
27 /* This routine uses the read_current_timer() 25 /* This routine uses the read_current_timer() routine and gets the
28 * loops per jiffy directly, instead of guessi 26 * loops per jiffy directly, instead of guessing it using delay().
29 * Also, this code tries to handle non-maskabl 27 * Also, this code tries to handle non-maskable asynchronous events
30 * (like SMIs) 28 * (like SMIs)
31 */ 29 */
32 #define DELAY_CALIBRATION_TICKS 30 #define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
33 #define MAX_DIRECT_CALIBRATION_RETRIES 31 #define MAX_DIRECT_CALIBRATION_RETRIES 5
34 32
35 static unsigned long calibrate_delay_direct(vo !! 33 static unsigned long __cpuinit calibrate_delay_direct(void)
36 { 34 {
37 unsigned long pre_start, start, post_s 35 unsigned long pre_start, start, post_start;
38 unsigned long pre_end, end, post_end; 36 unsigned long pre_end, end, post_end;
39 unsigned long start_jiffies; 37 unsigned long start_jiffies;
40 unsigned long timer_rate_min, timer_ra 38 unsigned long timer_rate_min, timer_rate_max;
41 unsigned long good_timer_sum = 0; 39 unsigned long good_timer_sum = 0;
42 unsigned long good_timer_count = 0; 40 unsigned long good_timer_count = 0;
43 unsigned long measured_times[MAX_DIREC <<
44 int max = -1; /* index of measured_tim <<
45 int min = -1; <<
46 int i; 41 int i;
47 42
48 if (read_current_timer(&pre_start) < 0 43 if (read_current_timer(&pre_start) < 0 )
49 return 0; 44 return 0;
50 45
51 /* 46 /*
52 * A simple loop like 47 * A simple loop like
53 * while ( jiffies < start_jiffie 48 * while ( jiffies < start_jiffies+1)
54 * start = read_current_t 49 * start = read_current_timer();
55 * will not do. As we don't really kno 50 * will not do. As we don't really know whether jiffy switch
56 * happened first or timer_value was r 51 * happened first or timer_value was read first. And some asynchronous
57 * event can happen between these two 52 * event can happen between these two events introducing errors in lpj.
58 * 53 *
59 * So, we do 54 * So, we do
60 * 1. pre_start <- When we are sure th 55 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
61 * 2. check jiffy switch 56 * 2. check jiffy switch
62 * 3. start <- timer value before or a 57 * 3. start <- timer value before or after jiffy switch
63 * 4. post_start <- When we are sure t 58 * 4. post_start <- When we are sure that jiffy switch has happened
64 * 59 *
65 * Note, we don't know anything about 60 * Note, we don't know anything about order of 2 and 3.
66 * Now, by looking at post_start and p 61 * Now, by looking at post_start and pre_start difference, we can
67 * check whether any asynchronous even 62 * check whether any asynchronous event happened or not
68 */ 63 */
69 64
70 for (i = 0; i < MAX_DIRECT_CALIBRATION 65 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
71 pre_start = 0; 66 pre_start = 0;
72 read_current_timer(&start); 67 read_current_timer(&start);
73 start_jiffies = jiffies; 68 start_jiffies = jiffies;
74 while (time_before_eq(jiffies, 69 while (time_before_eq(jiffies, start_jiffies + 1)) {
75 pre_start = start; 70 pre_start = start;
76 read_current_timer(&st 71 read_current_timer(&start);
77 } 72 }
78 read_current_timer(&post_start 73 read_current_timer(&post_start);
79 74
80 pre_end = 0; 75 pre_end = 0;
81 end = post_start; 76 end = post_start;
82 while (time_before_eq(jiffies, 77 while (time_before_eq(jiffies, start_jiffies + 1 +
83 78 DELAY_CALIBRATION_TICKS)) {
84 pre_end = end; 79 pre_end = end;
85 read_current_timer(&en 80 read_current_timer(&end);
86 } 81 }
87 read_current_timer(&post_end); 82 read_current_timer(&post_end);
88 83
89 timer_rate_max = (post_end - p 84 timer_rate_max = (post_end - pre_start) /
90 DELAY_ 85 DELAY_CALIBRATION_TICKS;
91 timer_rate_min = (pre_end - po 86 timer_rate_min = (pre_end - post_start) /
92 DELAY_ 87 DELAY_CALIBRATION_TICKS;
93 88
94 /* 89 /*
95 * If the upper limit and lowe 90 * If the upper limit and lower limit of the timer_rate is
96 * >= 12.5% apart, redo calibr 91 * >= 12.5% apart, redo calibration.
97 */ 92 */
98 if (start >= post_end) !! 93 if (pre_start != 0 && pre_end != 0 &&
99 printk(KERN_NOTICE "ca <<
100 "timer <<
101 " star <<
102 start, post_en <<
103 if (start < post_end && pre_st <<
104 (timer_rate_max - timer_ra 94 (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
105 good_timer_count++; 95 good_timer_count++;
106 good_timer_sum += time 96 good_timer_sum += timer_rate_max;
107 measured_times[i] = ti <<
108 if (max < 0 || timer_r <<
109 max = i; <<
110 if (min < 0 || timer_r <<
111 min = i; <<
112 } else <<
113 measured_times[i] = 0; <<
114 <<
115 } <<
116 <<
117 /* <<
118 * Find the maximum & minimum - if the <<
119 * one with the largest difference fro <<
120 */ <<
121 while (good_timer_count > 1) { <<
122 unsigned long estimate; <<
123 unsigned long maxdiff; <<
124 <<
125 /* compute the estimate */ <<
126 estimate = (good_timer_sum/goo <<
127 maxdiff = estimate >> 3; <<
128 <<
129 /* if range is within 12% let' <<
130 if ((measured_times[max] - mea <<
131 return estimate; <<
132 <<
133 /* ok - drop the worse value a <<
134 good_timer_sum = 0; <<
135 good_timer_count = 0; <<
136 if ((measured_times[max] - est <<
137 (estimate - me <<
138 printk(KERN_NOTICE "ca <<
139 "min b <<
140 min, measured_ <<
141 measured_times[min] = <<
142 min = max; <<
143 } else { <<
144 printk(KERN_NOTICE "ca <<
145 "max b <<
146 max, measured_ <<
147 measured_times[max] = <<
148 max = min; <<
149 } 97 }
150 <<
151 for (i = 0; i < MAX_DIRECT_CAL <<
152 if (measured_times[i] <<
153 continue; <<
154 good_timer_count++; <<
155 good_timer_sum += meas <<
156 if (measured_times[i] <<
157 min = i; <<
158 if (measured_times[i] <<
159 max = i; <<
160 } <<
161 <<
162 } 98 }
163 99
164 printk(KERN_NOTICE "calibrate_delay_di !! 100 if (good_timer_count)
165 "estimate for loops_per_jiffy.\ !! 101 return (good_timer_sum/good_timer_count);
166 "interrupts. Consider using \" !! 102
>> 103 printk(KERN_WARNING "calibrate_delay_direct() failed to get a good "
>> 104 "estimate for loops_per_jiffy.\nProbably due to long platform interrupts. Consider using \"lpj=\" boot option.\n");
167 return 0; 105 return 0;
168 } 106 }
169 #else 107 #else
170 static unsigned long calibrate_delay_direct(vo !! 108 static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
171 { <<
172 return 0; <<
173 } <<
174 #endif 109 #endif
175 110
176 /* 111 /*
177 * This is the number of bits of precision for 112 * This is the number of bits of precision for the loops_per_jiffy. Each
178 * time we refine our estimate after the first !! 113 * bit takes on average 1.5/HZ seconds. This (like the original) is a little
179 * to start with a good estimate. !! 114 * better than 1%
180 * For the boot cpu we can skip the delay cali 115 * For the boot cpu we can skip the delay calibration and assign it a value
181 * calculated based on the timer frequency. 116 * calculated based on the timer frequency.
182 * For the rest of the CPUs we cannot assume t 117 * For the rest of the CPUs we cannot assume that the timer frequency is same as
183 * the cpu frequency, hence do the calibration 118 * the cpu frequency, hence do the calibration for those.
184 */ 119 */
185 #define LPS_PREC 8 120 #define LPS_PREC 8
186 121
187 static unsigned long calibrate_delay_converge( !! 122 void __cpuinit calibrate_delay(void)
188 { <<
189 /* First stage - slowly accelerate to <<
190 unsigned long lpj, lpj_base, ticks, lo <<
191 int trials = 0, band = 0, trial_in_ban <<
192 <<
193 lpj = (1<<12); <<
194 <<
195 /* wait for "start of" clock tick */ <<
196 ticks = jiffies; <<
197 while (ticks == jiffies) <<
198 ; /* nothing */ <<
199 /* Go .. */ <<
200 ticks = jiffies; <<
201 do { <<
202 if (++trial_in_band == (1<<ban <<
203 ++band; <<
204 trial_in_band = 0; <<
205 } <<
206 __delay(lpj * band); <<
207 trials += band; <<
208 } while (ticks == jiffies); <<
209 /* <<
210 * We overshot, so retreat to a clear <<
211 * the largest likely undershoot. This <<
212 */ <<
213 trials -= band; <<
214 loopadd_base = lpj * band; <<
215 lpj_base = lpj * trials; <<
216 <<
217 recalibrate: <<
218 lpj = lpj_base; <<
219 loopadd = loopadd_base; <<
220 <<
221 /* <<
222 * Do a binary approximation to get lp <<
223 * equal one clock (up to LPS_PREC bit <<
224 */ <<
225 chop_limit = lpj >> LPS_PREC; <<
226 while (loopadd > chop_limit) { <<
227 lpj += loopadd; <<
228 ticks = jiffies; <<
229 while (ticks == jiffies) <<
230 ; /* nothing */ <<
231 ticks = jiffies; <<
232 __delay(lpj); <<
233 if (jiffies != ticks) /* lon <<
234 lpj -= loopadd; <<
235 loopadd >>= 1; <<
236 } <<
237 /* <<
238 * If we incremented every single time <<
239 * massively underestimated initially, <<
240 * start, and larger range. (Only seen <<
241 */ <<
242 if (lpj + loopadd * 2 == lpj_base + lo <<
243 lpj_base = lpj; <<
244 loopadd_base <<= 2; <<
245 goto recalibrate; <<
246 } <<
247 <<
248 return lpj; <<
249 } <<
250 <<
251 static DEFINE_PER_CPU(unsigned long, cpu_loops <<
252 <<
253 /* <<
254 * Check if cpu calibration delay is already k <<
255 * some processors with multi-core sockets may <<
256 * with the same calibration delay. <<
257 * <<
258 * Architectures should override this function <<
259 * method is available. <<
260 */ <<
261 unsigned long __attribute__((weak)) calibrate_ <<
262 { <<
263 return 0; <<
264 } <<
265 <<
266 /* <<
267 * Indicate the cpu delay calibration is done. <<
268 * architectures to stop accepting delay timer <<
269 */ <<
270 <<
271 void __attribute__((weak)) calibration_delay_d <<
272 { 123 {
273 } !! 124 unsigned long ticks, loopbit;
274 !! 125 int lps_precision = LPS_PREC;
275 void calibrate_delay(void) <<
276 { <<
277 unsigned long lpj; <<
278 static bool printed; 126 static bool printed;
279 int this_cpu = smp_processor_id(); <<
280 127
281 if (per_cpu(cpu_loops_per_jiffy, this_ !! 128 if (preset_lpj) {
282 lpj = per_cpu(cpu_loops_per_ji !! 129 loops_per_jiffy = preset_lpj;
283 if (!printed) <<
284 pr_info("Calibrating d <<
285 "already calib <<
286 } else if (preset_lpj) { <<
287 lpj = preset_lpj; <<
288 if (!printed) 130 if (!printed)
289 pr_info("Calibrating d 131 pr_info("Calibrating delay loop (skipped) "
290 "preset value. 132 "preset value.. ");
291 } else if ((!printed) && lpj_fine) { 133 } else if ((!printed) && lpj_fine) {
292 lpj = lpj_fine; !! 134 loops_per_jiffy = lpj_fine;
293 pr_info("Calibrating delay loo 135 pr_info("Calibrating delay loop (skipped), "
294 "value calculated usin 136 "value calculated using timer frequency.. ");
295 } else if ((lpj = calibrate_delay_is_k !! 137 } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
296 ; <<
297 } else if ((lpj = calibrate_delay_dire <<
298 if (!printed) 138 if (!printed)
299 pr_info("Calibrating d 139 pr_info("Calibrating delay using timer "
300 "specific rout 140 "specific routine.. ");
301 } else { 141 } else {
>> 142 loops_per_jiffy = (1<<12);
>> 143
302 if (!printed) 144 if (!printed)
303 pr_info("Calibrating d 145 pr_info("Calibrating delay loop... ");
304 lpj = calibrate_delay_converge !! 146 while ((loops_per_jiffy <<= 1) != 0) {
>> 147 /* wait for "start of" clock tick */
>> 148 ticks = jiffies;
>> 149 while (ticks == jiffies)
>> 150 /* nothing */;
>> 151 /* Go .. */
>> 152 ticks = jiffies;
>> 153 __delay(loops_per_jiffy);
>> 154 ticks = jiffies - ticks;
>> 155 if (ticks)
>> 156 break;
>> 157 }
>> 158
>> 159 /*
>> 160 * Do a binary approximation to get loops_per_jiffy set to
>> 161 * equal one clock (up to lps_precision bits)
>> 162 */
>> 163 loops_per_jiffy >>= 1;
>> 164 loopbit = loops_per_jiffy;
>> 165 while (lps_precision-- && (loopbit >>= 1)) {
>> 166 loops_per_jiffy |= loopbit;
>> 167 ticks = jiffies;
>> 168 while (ticks == jiffies)
>> 169 /* nothing */;
>> 170 ticks = jiffies;
>> 171 __delay(loops_per_jiffy);
>> 172 if (jiffies != ticks) /* longer than 1 tick */
>> 173 loops_per_jiffy &= ~loopbit;
>> 174 }
305 } 175 }
306 per_cpu(cpu_loops_per_jiffy, this_cpu) <<
307 if (!printed) 176 if (!printed)
308 pr_cont("%lu.%02lu BogoMIPS (l 177 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
309 lpj/(500000/HZ), !! 178 loops_per_jiffy/(500000/HZ),
310 (lpj/(5000/HZ)) % 100, !! 179 (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
311 180
312 loops_per_jiffy = lpj; <<
313 printed = true; 181 printed = true;
314 <<
315 calibration_delay_done(); <<
316 } 182 }
317 183
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.