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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/* calibrate.c: default delay calibration
2 *
3 * Excised from init/main.c
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
Tim Schmielaucd354f12007-02-14 00:33:14 -08007#include <linux/jiffies.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -07008#include <linux/delay.h>
9#include <linux/init.h>
Andrew Morton941e4922008-02-06 01:36:42 -080010#include <linux/timex.h>
Alok Kataria3da757d2008-06-20 15:06:33 -070011#include <linux/smp.h>
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070012
Alok Katariaf3f31492008-06-23 18:21:56 -070013unsigned long lpj_fine;
Randy Dunlapbfe8df32007-10-16 01:23:46 -070014unsigned long preset_lpj;
Linus Torvalds1da177e2005-04-16 15:20:36 -070015static int __init lpj_setup(char *str)
16{
17 preset_lpj = simple_strtoul(str,NULL,0);
18 return 1;
19}
20
21__setup("lpj=", lpj_setup);
22
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070023#ifdef ARCH_HAS_READ_CURRENT_TIMER
24
25/* This routine uses the read_current_timer() routine and gets the
26 * loops per jiffy directly, instead of guessing it using delay().
27 * Also, this code tries to handle non-maskable asynchronous events
28 * (like SMIs)
29 */
30#define DELAY_CALIBRATION_TICKS ((HZ < 100) ? 1 : (HZ/100))
31#define MAX_DIRECT_CALIBRATION_RETRIES 5
32
Adrian Bunk6c81c322008-02-06 01:37:51 -080033static unsigned long __cpuinit calibrate_delay_direct(void)
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070034{
35 unsigned long pre_start, start, post_start;
36 unsigned long pre_end, end, post_end;
37 unsigned long start_jiffies;
Alok Katariaf3f31492008-06-23 18:21:56 -070038 unsigned long timer_rate_min, timer_rate_max;
39 unsigned long good_timer_sum = 0;
40 unsigned long good_timer_count = 0;
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070041 int i;
42
43 if (read_current_timer(&pre_start) < 0 )
44 return 0;
45
46 /*
47 * A simple loop like
48 * while ( jiffies < start_jiffies+1)
49 * start = read_current_timer();
50 * will not do. As we don't really know whether jiffy switch
51 * happened first or timer_value was read first. And some asynchronous
52 * event can happen between these two events introducing errors in lpj.
53 *
54 * So, we do
55 * 1. pre_start <- When we are sure that jiffy switch hasn't happened
56 * 2. check jiffy switch
57 * 3. start <- timer value before or after jiffy switch
58 * 4. post_start <- When we are sure that jiffy switch has happened
59 *
60 * Note, we don't know anything about order of 2 and 3.
61 * Now, by looking at post_start and pre_start difference, we can
62 * check whether any asynchronous event happened or not
63 */
64
65 for (i = 0; i < MAX_DIRECT_CALIBRATION_RETRIES; i++) {
66 pre_start = 0;
67 read_current_timer(&start);
68 start_jiffies = jiffies;
Tim Deegan70a06222011-02-10 08:50:41 +000069 while (time_before_eq(jiffies, start_jiffies + 1)) {
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070070 pre_start = start;
71 read_current_timer(&start);
72 }
73 read_current_timer(&post_start);
74
75 pre_end = 0;
76 end = post_start;
Tim Deegan70a06222011-02-10 08:50:41 +000077 while (time_before_eq(jiffies, start_jiffies + 1 +
78 DELAY_CALIBRATION_TICKS)) {
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070079 pre_end = end;
80 read_current_timer(&end);
81 }
82 read_current_timer(&post_end);
83
Alok Katariaf3f31492008-06-23 18:21:56 -070084 timer_rate_max = (post_end - pre_start) /
85 DELAY_CALIBRATION_TICKS;
86 timer_rate_min = (pre_end - post_start) /
87 DELAY_CALIBRATION_TICKS;
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070088
89 /*
Alok Katariaf3f31492008-06-23 18:21:56 -070090 * If the upper limit and lower limit of the timer_rate is
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070091 * >= 12.5% apart, redo calibration.
92 */
93 if (pre_start != 0 && pre_end != 0 &&
Alok Katariaf3f31492008-06-23 18:21:56 -070094 (timer_rate_max - timer_rate_min) < (timer_rate_max >> 3)) {
95 good_timer_count++;
96 good_timer_sum += timer_rate_max;
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -070097 }
98 }
99
Alok Katariaf3f31492008-06-23 18:21:56 -0700100 if (good_timer_count)
101 return (good_timer_sum/good_timer_count);
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700102
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");
105 return 0;
106}
107#else
Adrian Bunk6c81c322008-02-06 01:37:51 -0800108static unsigned long __cpuinit calibrate_delay_direct(void) {return 0;}
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700109#endif
110
Linus Torvalds1da177e2005-04-16 15:20:36 -0700111/*
112 * This is the number of bits of precision for the loops_per_jiffy. Each
Phil Carmody191e5682011-03-22 16:34:13 -0700113 * time we refine our estimate after the first takes 1.5/HZ seconds, so try
114 * to start with a good estimate.
Alok Kataria3da757d2008-06-20 15:06:33 -0700115 * For the boot cpu we can skip the delay calibration and assign it a value
Alok Katariaf3f31492008-06-23 18:21:56 -0700116 * calculated based on the timer frequency.
117 * For the rest of the CPUs we cannot assume that the timer frequency is same as
Alok Kataria3da757d2008-06-20 15:06:33 -0700118 * the cpu frequency, hence do the calibration for those.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119 */
120#define LPS_PREC 8
121
Phil Carmody71c696b2011-03-22 16:34:12 -0700122static unsigned long __cpuinit calibrate_delay_converge(void)
123{
Phil Carmody191e5682011-03-22 16:34:13 -0700124 /* First stage - slowly accelerate to find initial bounds */
125 unsigned long lpj, ticks, loopadd, chop_limit;
126 int trials = 0, band = 0, trial_in_band = 0;
Phil Carmody71c696b2011-03-22 16:34:12 -0700127
128 lpj = (1<<12);
Phil Carmody191e5682011-03-22 16:34:13 -0700129
130 /* wait for "start of" clock tick */
131 ticks = jiffies;
132 while (ticks == jiffies)
133 ; /* nothing */
134 /* Go .. */
135 ticks = jiffies;
136 do {
137 if (++trial_in_band == (1<<band)) {
138 ++band;
139 trial_in_band = 0;
140 }
141 __delay(lpj * band);
142 trials += band;
143 } while (ticks == jiffies);
144 /*
145 * We overshot, so retreat to a clear underestimate. Then estimate
146 * the largest likely undershoot. This defines our chop bounds.
147 */
148 trials -= band;
149 loopadd = lpj * band;
150 lpj *= trials;
151 chop_limit = lpj >> (LPS_PREC + 1);
Phil Carmody71c696b2011-03-22 16:34:12 -0700152
153 /*
154 * Do a binary approximation to get lpj set to
Phil Carmody191e5682011-03-22 16:34:13 -0700155 * equal one clock (up to LPS_PREC bits)
Phil Carmody71c696b2011-03-22 16:34:12 -0700156 */
Phil Carmody191e5682011-03-22 16:34:13 -0700157 while (loopadd > chop_limit) {
158 lpj += loopadd;
Phil Carmody71c696b2011-03-22 16:34:12 -0700159 ticks = jiffies;
160 while (ticks == jiffies)
Phil Carmody191e5682011-03-22 16:34:13 -0700161 ; /* nothing */
Phil Carmody71c696b2011-03-22 16:34:12 -0700162 ticks = jiffies;
163 __delay(lpj);
164 if (jiffies != ticks) /* longer than 1 tick */
Phil Carmody191e5682011-03-22 16:34:13 -0700165 lpj -= loopadd;
166 loopadd >>= 1;
Phil Carmody71c696b2011-03-22 16:34:12 -0700167 }
168
169 return lpj;
170}
171
Adrian Bunk6c81c322008-02-06 01:37:51 -0800172void __cpuinit calibrate_delay(void)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700173{
Mike Travisfeae3202009-11-17 18:22:13 -0600174 static bool printed;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700175
176 if (preset_lpj) {
177 loops_per_jiffy = preset_lpj;
Mike Travisfeae3202009-11-17 18:22:13 -0600178 if (!printed)
179 pr_info("Calibrating delay loop (skipped) "
180 "preset value.. ");
181 } else if ((!printed) && lpj_fine) {
Alok Katariaf3f31492008-06-23 18:21:56 -0700182 loops_per_jiffy = lpj_fine;
Mike Travisfeae3202009-11-17 18:22:13 -0600183 pr_info("Calibrating delay loop (skipped), "
Alok Katariaf3f31492008-06-23 18:21:56 -0700184 "value calculated using timer frequency.. ");
Venkatesh Pallipadi8a9e1b02005-06-23 00:08:13 -0700185 } else if ((loops_per_jiffy = calibrate_delay_direct()) != 0) {
Mike Travisfeae3202009-11-17 18:22:13 -0600186 if (!printed)
187 pr_info("Calibrating delay using timer "
188 "specific routine.. ");
Linus Torvalds1da177e2005-04-16 15:20:36 -0700189 } else {
Mike Travisfeae3202009-11-17 18:22:13 -0600190 if (!printed)
191 pr_info("Calibrating delay loop... ");
Phil Carmody71c696b2011-03-22 16:34:12 -0700192 loops_per_jiffy = calibrate_delay_converge();
Linus Torvalds1da177e2005-04-16 15:20:36 -0700193 }
Mike Travisfeae3202009-11-17 18:22:13 -0600194 if (!printed)
195 pr_cont("%lu.%02lu BogoMIPS (lpj=%lu)\n",
Alok Kataria3da757d2008-06-20 15:06:33 -0700196 loops_per_jiffy/(500000/HZ),
197 (loops_per_jiffy/(5000/HZ)) % 100, loops_per_jiffy);
Mike Travisfeae3202009-11-17 18:22:13 -0600198
199 printed = true;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700200}