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a75244c3 PO |
1 | /* |
2 | * Copyright (C) 2009 Intel Corporation. | |
3 | * Author: Patrick Ohly <patrick.ohly@intel.com> | |
4 | * | |
5 | * This program is free software; you can redistribute it and/or modify | |
6 | * it under the terms of the GNU General Public License as published by | |
7 | * the Free Software Foundation; either version 2 of the License, or | |
8 | * (at your option) any later version. | |
9 | * | |
10 | * This program is distributed in the hope that it will be useful, | |
11 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | * GNU General Public License for more details. | |
14 | * | |
15 | * You should have received a copy of the GNU General Public License | |
16 | * along with this program; if not, write to the Free Software | |
17 | * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. | |
18 | */ | |
19 | ||
20 | #include <linux/timecompare.h> | |
21 | #include <linux/module.h> | |
22 | #include <linux/math64.h> | |
23 | ||
24 | /* | |
25 | * fixed point arithmetic scale factor for skew | |
26 | * | |
27 | * Usually one would measure skew in ppb (parts per billion, 1e9), but | |
28 | * using a factor of 2 simplifies the math. | |
29 | */ | |
30 | #define TIMECOMPARE_SKEW_RESOLUTION (((s64)1)<<30) | |
31 | ||
32 | ktime_t timecompare_transform(struct timecompare *sync, | |
33 | u64 source_tstamp) | |
34 | { | |
35 | u64 nsec; | |
36 | ||
37 | nsec = source_tstamp + sync->offset; | |
38 | nsec += (s64)(source_tstamp - sync->last_update) * sync->skew / | |
39 | TIMECOMPARE_SKEW_RESOLUTION; | |
40 | ||
41 | return ns_to_ktime(nsec); | |
42 | } | |
3586e0a9 | 43 | EXPORT_SYMBOL_GPL(timecompare_transform); |
a75244c3 PO |
44 | |
45 | int timecompare_offset(struct timecompare *sync, | |
46 | s64 *offset, | |
47 | u64 *source_tstamp) | |
48 | { | |
49 | u64 start_source = 0, end_source = 0; | |
50 | struct { | |
51 | s64 offset; | |
52 | s64 duration_target; | |
53 | } buffer[10], sample, *samples; | |
54 | int counter = 0, i; | |
55 | int used; | |
56 | int index; | |
57 | int num_samples = sync->num_samples; | |
58 | ||
59 | if (num_samples > sizeof(buffer)/sizeof(buffer[0])) { | |
60 | samples = kmalloc(sizeof(*samples) * num_samples, GFP_ATOMIC); | |
61 | if (!samples) { | |
62 | samples = buffer; | |
63 | num_samples = sizeof(buffer)/sizeof(buffer[0]); | |
64 | } | |
65 | } else { | |
66 | samples = buffer; | |
67 | } | |
68 | ||
69 | /* run until we have enough valid samples, but do not try forever */ | |
70 | i = 0; | |
71 | counter = 0; | |
72 | while (1) { | |
73 | u64 ts; | |
74 | ktime_t start, end; | |
75 | ||
76 | start = sync->target(); | |
77 | ts = timecounter_read(sync->source); | |
78 | end = sync->target(); | |
79 | ||
80 | if (!i) | |
81 | start_source = ts; | |
82 | ||
83 | /* ignore negative durations */ | |
84 | sample.duration_target = ktime_to_ns(ktime_sub(end, start)); | |
85 | if (sample.duration_target >= 0) { | |
86 | /* | |
87 | * assume symetric delay to and from source: | |
88 | * average target time corresponds to measured | |
89 | * source time | |
90 | */ | |
91 | sample.offset = | |
f065f41f | 92 | (ktime_to_ns(end) + ktime_to_ns(start)) / 2 - |
a75244c3 PO |
93 | ts; |
94 | ||
95 | /* simple insertion sort based on duration */ | |
96 | index = counter - 1; | |
97 | while (index >= 0) { | |
98 | if (samples[index].duration_target < | |
99 | sample.duration_target) | |
100 | break; | |
101 | samples[index + 1] = samples[index]; | |
102 | index--; | |
103 | } | |
104 | samples[index + 1] = sample; | |
105 | counter++; | |
106 | } | |
107 | ||
108 | i++; | |
109 | if (counter >= num_samples || i >= 100000) { | |
110 | end_source = ts; | |
111 | break; | |
112 | } | |
113 | } | |
114 | ||
115 | *source_tstamp = (end_source + start_source) / 2; | |
116 | ||
117 | /* remove outliers by only using 75% of the samples */ | |
118 | used = counter * 3 / 4; | |
119 | if (!used) | |
120 | used = counter; | |
121 | if (used) { | |
122 | /* calculate average */ | |
123 | s64 off = 0; | |
124 | for (index = 0; index < used; index++) | |
125 | off += samples[index].offset; | |
126 | *offset = div_s64(off, used); | |
127 | } | |
128 | ||
129 | if (samples && samples != buffer) | |
130 | kfree(samples); | |
131 | ||
132 | return used; | |
133 | } | |
3586e0a9 | 134 | EXPORT_SYMBOL_GPL(timecompare_offset); |
a75244c3 PO |
135 | |
136 | void __timecompare_update(struct timecompare *sync, | |
137 | u64 source_tstamp) | |
138 | { | |
139 | s64 offset; | |
140 | u64 average_time; | |
141 | ||
142 | if (!timecompare_offset(sync, &offset, &average_time)) | |
143 | return; | |
144 | ||
145 | if (!sync->last_update) { | |
146 | sync->last_update = average_time; | |
147 | sync->offset = offset; | |
148 | sync->skew = 0; | |
149 | } else { | |
150 | s64 delta_nsec = average_time - sync->last_update; | |
151 | ||
152 | /* avoid division by negative or small deltas */ | |
153 | if (delta_nsec >= 10000) { | |
154 | s64 delta_offset_nsec = offset - sync->offset; | |
155 | s64 skew; /* delta_offset_nsec * | |
156 | TIMECOMPARE_SKEW_RESOLUTION / | |
157 | delta_nsec */ | |
158 | u64 divisor; | |
159 | ||
160 | /* div_s64() is limited to 32 bit divisor */ | |
161 | skew = delta_offset_nsec * TIMECOMPARE_SKEW_RESOLUTION; | |
162 | divisor = delta_nsec; | |
163 | while (unlikely(divisor >= ((s64)1) << 32)) { | |
164 | /* divide both by 2; beware, right shift | |
165 | of negative value has undefined | |
166 | behavior and can only be used for | |
167 | the positive divisor */ | |
168 | skew = div_s64(skew, 2); | |
169 | divisor >>= 1; | |
170 | } | |
171 | skew = div_s64(skew, divisor); | |
172 | ||
173 | /* | |
174 | * Calculate new overall skew as 4/16 the | |
175 | * old value and 12/16 the new one. This is | |
176 | * a rather arbitrary tradeoff between | |
177 | * only using the latest measurement (0/16 and | |
178 | * 16/16) and even more weight on past measurements. | |
179 | */ | |
180 | #define TIMECOMPARE_NEW_SKEW_PER_16 12 | |
181 | sync->skew = | |
182 | div_s64((16 - TIMECOMPARE_NEW_SKEW_PER_16) * | |
183 | sync->skew + | |
184 | TIMECOMPARE_NEW_SKEW_PER_16 * skew, | |
185 | 16); | |
186 | sync->last_update = average_time; | |
187 | sync->offset = offset; | |
188 | } | |
189 | } | |
190 | } | |
3586e0a9 | 191 | EXPORT_SYMBOL_GPL(__timecompare_update); |