1 // SPDX-License-Identifier: GPL-2.0 1 // SPDX-License-Identifier: GPL-2.0
2 /* calibrate.c: default delay calibration 2 /* calibrate.c: default delay calibration
3 * 3 *
4 * Excised from init/main.c 4 * Excised from init/main.c
5 * Copyright (C) 1991, 1992 Linus Torvalds 5 * Copyright (C) 1991, 1992 Linus Torvalds
6 */ 6 */
7 7
8 #include <linux/jiffies.h> 8 #include <linux/jiffies.h>
9 #include <linux/delay.h> 9 #include <linux/delay.h>
10 #include <linux/init.h> 10 #include <linux/init.h>
11 #include <linux/timex.h> 11 #include <linux/timex.h>
12 #include <linux/smp.h> 12 #include <linux/smp.h>
13 #include <linux/percpu.h> 13 #include <linux/percpu.h>
14 14
15 unsigned long lpj_fine; 15 unsigned long lpj_fine;
16 unsigned long preset_lpj; 16 unsigned long preset_lpj;
17 static int __init lpj_setup(char *str) 17 static int __init lpj_setup(char *str)
18 { 18 {
19 preset_lpj = simple_strtoul(str,NULL,0 19 preset_lpj = simple_strtoul(str,NULL,0);
20 return 1; 20 return 1;
21 } 21 }
22 22
23 __setup("lpj=", lpj_setup); 23 __setup("lpj=", lpj_setup);
24 24
25 #ifdef ARCH_HAS_READ_CURRENT_TIMER 25 #ifdef ARCH_HAS_READ_CURRENT_TIMER
26 26
27 /* This routine uses the read_current_timer() 27 /* This routine uses the read_current_timer() routine and gets the
28 * loops per jiffy directly, instead of guessi 28 * loops per jiffy directly, instead of guessing it using delay().
29 * Also, this code tries to handle non-maskabl 29 * Also, this code tries to handle non-maskable asynchronous events
30 * (like SMIs) 30 * (like SMIs)
31 */ 31 */
32 #define DELAY_CALIBRATION_TICKS 32 #define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
33 #define MAX_DIRECT_CALIBRATION_RETRIES 33 #define MAX_DIRECT_CALIBRATION_RETRIES 5
34 34
35 static unsigned long calibrate_delay_direct(vo 35 static unsigned long calibrate_delay_direct(void)
36 { 36 {
37 unsigned long pre_start, start, post_s 37 unsigned long pre_start, start, post_start;
38 unsigned long pre_end, end, post_end; 38 unsigned long pre_end, end, post_end;
39 unsigned long start_jiffies; 39 unsigned long start_jiffies;
40 unsigned long timer_rate_min, timer_ra 40 unsigned long timer_rate_min, timer_rate_max;
41 unsigned long good_timer_sum = 0; 41 unsigned long good_timer_sum = 0;
42 unsigned long good_timer_count = 0; 42 unsigned long good_timer_count = 0;
43 unsigned long measured_times[MAX_DIREC 43 unsigned long measured_times[MAX_DIRECT_CALIBRATION_RETRIES];
44 int max = -1; /* index of measured_tim 44 int max = -1; /* index of measured_times with max/min values or not set */
45 int min = -1; 45 int min = -1;
46 int i; 46 int i;
47 47
48 if (read_current_timer(&pre_start) < 0 48 if (read_current_timer(&pre_start) < 0 )
49 return 0; 49 return 0;
50 50
51 /* 51 /*
52 * A simple loop like 52 * A simple loop like
53 * while ( jiffies < start_jiffie 53 * while ( jiffies < start_jiffies+1)
54 * start = read_current_t 54 * start = read_current_timer();
55 * will not do. As we don't really kno 55 * will not do. As we don't really know whether jiffy switch
56 * happened first or timer_value was r 56 * happened first or timer_value was read first. And some asynchronous
57 * event can happen between these two 57 * event can happen between these two events introducing errors in lpj.
58 * 58 *
59 * So, we do 59 * So, we do
60 * 1. pre_start <- When we are sure th 60 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
61 * 2. check jiffy switch 61 * 2. check jiffy switch
62 * 3. start <- timer value before or a 62 * 3. start <- timer value before or after jiffy switch
63 * 4. post_start <- When we are sure t 63 * 4. post_start <- When we are sure that jiffy switch has happened
64 * 64 *
65 * Note, we don't know anything about 65 * Note, we don't know anything about order of 2 and 3.
66 * Now, by looking at post_start and p 66 * Now, by looking at post_start and pre_start difference, we can
67 * check whether any asynchronous even 67 * check whether any asynchronous event happened or not
68 */ 68 */
69 69
70 for (i = 0; i < MAX_DIRECT_CALIBRATION 70 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
71 pre_start = 0; 71 pre_start = 0;
72 read_current_timer(&start); 72 read_current_timer(&start);
73 start_jiffies = jiffies; 73 start_jiffies = jiffies;
74 while (time_before_eq(jiffies, 74 while (time_before_eq(jiffies, start_jiffies + 1)) {
75 pre_start = start; 75 pre_start = start;
76 read_current_timer(&st 76 read_current_timer(&start);
77 } 77 }
78 read_current_timer(&post_start 78 read_current_timer(&post_start);
79 79
80 pre_end = 0; 80 pre_end = 0;
81 end = post_start; 81 end = post_start;
82 while (time_before_eq(jiffies, 82 while (time_before_eq(jiffies, start_jiffies + 1 +
83 83 DELAY_CALIBRATION_TICKS)) {
84 pre_end = end; 84 pre_end = end;
85 read_current_timer(&en 85 read_current_timer(&end);
86 } 86 }
87 read_current_timer(&post_end); 87 read_current_timer(&post_end);
88 88
89 timer_rate_max = (post_end - p 89 timer_rate_max = (post_end - pre_start) /
90 DELAY_ 90 DELAY_CALIBRATION_TICKS;
91 timer_rate_min = (pre_end - po 91 timer_rate_min = (pre_end - post_start) /
92 DELAY_ 92 DELAY_CALIBRATION_TICKS;
93 93
94 /* 94 /*
95 * If the upper limit and lowe 95 * If the upper limit and lower limit of the timer_rate is
96 * >= 12.5% apart, redo calibr 96 * >= 12.5% apart, redo calibration.
97 */ 97 */
98 if (start >= post_end) 98 if (start >= post_end)
99 printk(KERN_NOTICE "ca 99 printk(KERN_NOTICE "calibrate_delay_direct() ignoring "
100 "timer 100 "timer_rate as we had a TSC wrap around"
101 " star 101 " start=%lu >=post_end=%lu\n",
102 start, post_en 102 start, post_end);
103 if (start < post_end && pre_st 103 if (start < post_end && pre_start != 0 && pre_end != 0 &&
104 (timer_rate_max - timer_ra 104 (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
105 good_timer_count++; 105 good_timer_count++;
106 good_timer_sum += time 106 good_timer_sum += timer_rate_max;
107 measured_times[i] = ti 107 measured_times[i] = timer_rate_max;
108 if (max < 0 || timer_r 108 if (max < 0 || timer_rate_max > measured_times[max])
109 max = i; 109 max = i;
110 if (min < 0 || timer_r 110 if (min < 0 || timer_rate_max < measured_times[min])
111 min = i; 111 min = i;
112 } else 112 } else
113 measured_times[i] = 0; 113 measured_times[i] = 0;
114 114
115 } 115 }
116 116
117 /* 117 /*
118 * Find the maximum & minimum - if the 118 * Find the maximum & minimum - if they differ too much throw out the
119 * one with the largest difference fro 119 * one with the largest difference from the mean and try again...
120 */ 120 */
121 while (good_timer_count > 1) { 121 while (good_timer_count > 1) {
122 unsigned long estimate; 122 unsigned long estimate;
123 unsigned long maxdiff; 123 unsigned long maxdiff;
124 124
125 /* compute the estimate */ 125 /* compute the estimate */
126 estimate = (good_timer_sum/goo 126 estimate = (good_timer_sum/good_timer_count);
127 maxdiff = estimate >> 3; 127 maxdiff = estimate >> 3;
128 128
129 /* if range is within 12% let' 129 /* if range is within 12% let's take it */
130 if ((measured_times[max] - mea 130 if ((measured_times[max] - measured_times[min]) < maxdiff)
131 return estimate; 131 return estimate;
132 132
133 /* ok - drop the worse value a 133 /* ok - drop the worse value and try again... */
134 good_timer_sum = 0; 134 good_timer_sum = 0;
135 good_timer_count = 0; 135 good_timer_count = 0;
136 if ((measured_times[max] - est 136 if ((measured_times[max] - estimate) <
137 (estimate - me 137 (estimate - measured_times[min])) {
138 printk(KERN_NOTICE "ca 138 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
139 "min b 139 "min bogoMips estimate %d = %lu\n",
140 min, measured_ 140 min, measured_times[min]);
141 measured_times[min] = 141 measured_times[min] = 0;
142 min = max; 142 min = max;
143 } else { 143 } else {
144 printk(KERN_NOTICE "ca 144 printk(KERN_NOTICE "calibrate_delay_direct() dropping "
145 "max b 145 "max bogoMips estimate %d = %lu\n",
146 max, measured_ 146 max, measured_times[max]);
147 measured_times[max] = 147 measured_times[max] = 0;
148 max = min; 148 max = min;
149 } 149 }
150 150
151 for (i = 0; i < MAX_DIRECT_CAL 151 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
152 if (measured_times[i] 152 if (measured_times[i] == 0)
153 continue; 153 continue;
154 good_timer_count++; 154 good_timer_count++;
155 good_timer_sum += meas 155 good_timer_sum += measured_times[i];
156 if (measured_times[i] 156 if (measured_times[i] < measured_times[min])
157 min = i; 157 min = i;
158 if (measured_times[i] 158 if (measured_times[i] > measured_times[max])
159 max = i; 159 max = i;
160 } 160 }
161 161
162 } 162 }
163 163
164 printk(KERN_NOTICE "calibrate_delay_di 164 printk(KERN_NOTICE "calibrate_delay_direct() failed to get a good "
165 "estimate for loops_per_jiffy.\ 165 "estimate for loops_per_jiffy.\nProbably due to long platform "
166 "interrupts. Consider using \" 166 "interrupts. Consider using \"lpj=\" boot option.\n");
167 return 0; 167 return 0;
168 } 168 }
169 #else 169 #else
170 static unsigned long calibrate_delay_direct(vo 170 static unsigned long calibrate_delay_direct(void)
171 { 171 {
172 return 0; 172 return 0;
173 } 173 }
174 #endif 174 #endif
175 175
176 /* 176 /*
177 * This is the number of bits of precision for 177 * This is the number of bits of precision for the loops_per_jiffy. Each
178 * time we refine our estimate after the first 178 * time we refine our estimate after the first takes 1.5/HZ seconds, so try
179 * to start with a good estimate. 179 * to start with a good estimate.
180 * For the boot cpu we can skip the delay cali 180 * For the boot cpu we can skip the delay calibration and assign it a value
181 * calculated based on the timer frequency. 181 * calculated based on the timer frequency.
182 * For the rest of the CPUs we cannot assume t 182 * For the rest of the CPUs we cannot assume that the timer frequency is same as
183 * the cpu frequency, hence do the calibration 183 * the cpu frequency, hence do the calibration for those.
184 */ 184 */
185 #define LPS_PREC 8 185 #define LPS_PREC 8
186 186
187 static unsigned long calibrate_delay_converge( 187 static unsigned long calibrate_delay_converge(void)
188 { 188 {
189 /* First stage - slowly accelerate to 189 /* First stage - slowly accelerate to find initial bounds */
190 unsigned long lpj, lpj_base, ticks, lo 190 unsigned long lpj, lpj_base, ticks, loopadd, loopadd_base, chop_limit;
191 int trials = 0, band = 0, trial_in_ban 191 int trials = 0, band = 0, trial_in_band = 0;
192 192
193 lpj = (1<<12); 193 lpj = (1<<12);
194 194
195 /* wait for "start of" clock tick */ 195 /* wait for "start of" clock tick */
196 ticks = jiffies; 196 ticks = jiffies;
197 while (ticks == jiffies) 197 while (ticks == jiffies)
198 ; /* nothing */ 198 ; /* nothing */
199 /* Go .. */ 199 /* Go .. */
200 ticks = jiffies; 200 ticks = jiffies;
201 do { 201 do {
202 if (++trial_in_band == (1<<ban 202 if (++trial_in_band == (1<<band)) {
203 ++band; 203 ++band;
204 trial_in_band = 0; 204 trial_in_band = 0;
205 } 205 }
206 __delay(lpj * band); 206 __delay(lpj * band);
207 trials += band; 207 trials += band;
208 } while (ticks == jiffies); 208 } while (ticks == jiffies);
209 /* 209 /*
210 * We overshot, so retreat to a clear 210 * We overshot, so retreat to a clear underestimate. Then estimate
211 * the largest likely undershoot. This 211 * the largest likely undershoot. This defines our chop bounds.
212 */ 212 */
213 trials -= band; 213 trials -= band;
214 loopadd_base = lpj * band; 214 loopadd_base = lpj * band;
215 lpj_base = lpj * trials; 215 lpj_base = lpj * trials;
216 216
217 recalibrate: 217 recalibrate:
218 lpj = lpj_base; 218 lpj = lpj_base;
219 loopadd = loopadd_base; 219 loopadd = loopadd_base;
220 220
221 /* 221 /*
222 * Do a binary approximation to get lp 222 * Do a binary approximation to get lpj set to
223 * equal one clock (up to LPS_PREC bit 223 * equal one clock (up to LPS_PREC bits)
224 */ 224 */
225 chop_limit = lpj >> LPS_PREC; 225 chop_limit = lpj >> LPS_PREC;
226 while (loopadd > chop_limit) { 226 while (loopadd > chop_limit) {
227 lpj += loopadd; 227 lpj += loopadd;
228 ticks = jiffies; 228 ticks = jiffies;
229 while (ticks == jiffies) 229 while (ticks == jiffies)
230 ; /* nothing */ 230 ; /* nothing */
231 ticks = jiffies; 231 ticks = jiffies;
232 __delay(lpj); 232 __delay(lpj);
233 if (jiffies != ticks) /* lon 233 if (jiffies != ticks) /* longer than 1 tick */
234 lpj -= loopadd; 234 lpj -= loopadd;
235 loopadd >>= 1; 235 loopadd >>= 1;
236 } 236 }
237 /* 237 /*
238 * If we incremented every single time 238 * If we incremented every single time possible, presume we've
239 * massively underestimated initially, 239 * massively underestimated initially, and retry with a higher
240 * start, and larger range. (Only seen 240 * start, and larger range. (Only seen on x86_64, due to SMIs)
241 */ 241 */
242 if (lpj + loopadd * 2 == lpj_base + lo 242 if (lpj + loopadd * 2 == lpj_base + loopadd_base * 2) {
243 lpj_base = lpj; 243 lpj_base = lpj;
244 loopadd_base <<= 2; 244 loopadd_base <<= 2;
245 goto recalibrate; 245 goto recalibrate;
246 } 246 }
247 247
248 return lpj; 248 return lpj;
249 } 249 }
250 250
251 static DEFINE_PER_CPU(unsigned long, cpu_loops 251 static DEFINE_PER_CPU(unsigned long, cpu_loops_per_jiffy) = { 0 };
252 252
253 /* 253 /*
254 * Check if cpu calibration delay is already k 254 * Check if cpu calibration delay is already known. For example,
255 * some processors with multi-core sockets may 255 * some processors with multi-core sockets may have all cores
256 * with the same calibration delay. 256 * with the same calibration delay.
257 * 257 *
258 * Architectures should override this function 258 * Architectures should override this function if a faster calibration
259 * method is available. 259 * method is available.
260 */ 260 */
261 unsigned long __attribute__((weak)) calibrate_ 261 unsigned long __attribute__((weak)) calibrate_delay_is_known(void)
262 { 262 {
263 return 0; 263 return 0;
264 } 264 }
265 265
266 /* 266 /*
267 * Indicate the cpu delay calibration is done. 267 * Indicate the cpu delay calibration is done. This can be used by
268 * architectures to stop accepting delay timer 268 * architectures to stop accepting delay timer registrations after this point.
269 */ 269 */
270 270
271 void __attribute__((weak)) calibration_delay_d 271 void __attribute__((weak)) calibration_delay_done(void)
272 { 272 {
273 } 273 }
274 274
275 void calibrate_delay(void) 275 void calibrate_delay(void)
276 { 276 {
277 unsigned long lpj; 277 unsigned long lpj;
278 static bool printed; 278 static bool printed;
279 int this_cpu = smp_processor_id(); 279 int this_cpu = smp_processor_id();
280 280
281 if (per_cpu(cpu_loops_per_jiffy, this_ 281 if (per_cpu(cpu_loops_per_jiffy, this_cpu)) {
282 lpj = per_cpu(cpu_loops_per_ji 282 lpj = per_cpu(cpu_loops_per_jiffy, this_cpu);
283 if (!printed) 283 if (!printed)
284 pr_info("Calibrating d 284 pr_info("Calibrating delay loop (skipped) "
285 "already calib 285 "already calibrated this CPU");
286 } else if (preset_lpj) { 286 } else if (preset_lpj) {
287 lpj = preset_lpj; 287 lpj = preset_lpj;
288 if (!printed) 288 if (!printed)
289 pr_info("Calibrating d 289 pr_info("Calibrating delay loop (skipped) "
290 "preset value. 290 "preset value.. ");
291 } else if ((!printed) && lpj_fine) { 291 } else if ((!printed) && lpj_fine) {
292 lpj = lpj_fine; 292 lpj = lpj_fine;
293 pr_info("Calibrating delay loo 293 pr_info("Calibrating delay loop (skipped), "
294 "value calculated usin 294 "value calculated using timer frequency.. ");
295 } else if ((lpj = calibrate_delay_is_k 295 } else if ((lpj = calibrate_delay_is_known())) {
296 ; 296 ;
297 } else if ((lpj = calibrate_delay_dire 297 } else if ((lpj = calibrate_delay_direct()) != 0) {
298 if (!printed) 298 if (!printed)
299 pr_info("Calibrating d 299 pr_info("Calibrating delay using timer "
300 "specific rout 300 "specific routine.. ");
301 } else { 301 } else {
302 if (!printed) 302 if (!printed)
303 pr_info("Calibrating d 303 pr_info("Calibrating delay loop... ");
304 lpj = calibrate_delay_converge 304 lpj = calibrate_delay_converge();
305 } 305 }
306 per_cpu(cpu_loops_per_jiffy, this_cpu) 306 per_cpu(cpu_loops_per_jiffy, this_cpu) = lpj;
307 if (!printed) 307 if (!printed)
308 pr_cont("%lu.%02lu BogoMIPS (l 308 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
309 lpj/(500000/HZ), 309 lpj/(500000/HZ),
310 (lpj/(5000/HZ)) % 100, 310 (lpj/(5000/HZ)) % 100, lpj);
311 311
312 loops_per_jiffy = lpj; 312 loops_per_jiffy = lpj;
313 printed = true; 313 printed = true;
314 314
315 calibration_delay_done(); 315 calibration_delay_done();
316 } 316 }
317 317
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