media: tegra: Tegra videobuf2
[linux-2.6.git] / kernel / time / timecompare.c
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/slab.h>
23 #include <linux/math64.h>
24 #include <linux/kernel.h>
25
26 /*
27  * fixed point arithmetic scale factor for skew
28  *
29  * Usually one would measure skew in ppb (parts per billion, 1e9), but
30  * using a factor of 2 simplifies the math.
31  */
32 #define TIMECOMPARE_SKEW_RESOLUTION (((s64)1)<<30)
33
34 ktime_t timecompare_transform(struct timecompare *sync,
35                               u64 source_tstamp)
36 {
37         u64 nsec;
38
39         nsec = source_tstamp + sync->offset;
40         nsec += (s64)(source_tstamp - sync->last_update) * sync->skew /
41                 TIMECOMPARE_SKEW_RESOLUTION;
42
43         return ns_to_ktime(nsec);
44 }
45 EXPORT_SYMBOL_GPL(timecompare_transform);
46
47 int timecompare_offset(struct timecompare *sync,
48                        s64 *offset,
49                        u64 *source_tstamp)
50 {
51         u64 start_source = 0, end_source = 0;
52         struct {
53                 s64 offset;
54                 s64 duration_target;
55         } buffer[10], sample, *samples;
56         int counter = 0, i;
57         int used;
58         int index;
59         int num_samples = sync->num_samples;
60
61         if (num_samples > ARRAY_SIZE(buffer)) {
62                 samples = kmalloc(sizeof(*samples) * num_samples, GFP_ATOMIC);
63                 if (!samples) {
64                         samples = buffer;
65                         num_samples = ARRAY_SIZE(buffer);
66                 }
67         } else {
68                 samples = buffer;
69         }
70
71         /* run until we have enough valid samples, but do not try forever */
72         i = 0;
73         counter = 0;
74         while (1) {
75                 u64 ts;
76                 ktime_t start, end;
77
78                 start = sync->target();
79                 ts = timecounter_read(sync->source);
80                 end = sync->target();
81
82                 if (!i)
83                         start_source = ts;
84
85                 /* ignore negative durations */
86                 sample.duration_target = ktime_to_ns(ktime_sub(end, start));
87                 if (sample.duration_target >= 0) {
88                         /*
89                          * assume symetric delay to and from source:
90                          * average target time corresponds to measured
91                          * source time
92                          */
93                         sample.offset =
94                                 (ktime_to_ns(end) + ktime_to_ns(start)) / 2 -
95                                 ts;
96
97                         /* simple insertion sort based on duration */
98                         index = counter - 1;
99                         while (index >= 0) {
100                                 if (samples[index].duration_target <
101                                     sample.duration_target)
102                                         break;
103                                 samples[index + 1] = samples[index];
104                                 index--;
105                         }
106                         samples[index + 1] = sample;
107                         counter++;
108                 }
109
110                 i++;
111                 if (counter >= num_samples || i >= 100000) {
112                         end_source = ts;
113                         break;
114                 }
115         }
116
117         *source_tstamp = (end_source + start_source) / 2;
118
119         /* remove outliers by only using 75% of the samples */
120         used = counter * 3 / 4;
121         if (!used)
122                 used = counter;
123         if (used) {
124                 /* calculate average */
125                 s64 off = 0;
126                 for (index = 0; index < used; index++)
127                         off += samples[index].offset;
128                 *offset = div_s64(off, used);
129         }
130
131         if (samples && samples != buffer)
132                 kfree(samples);
133
134         return used;
135 }
136 EXPORT_SYMBOL_GPL(timecompare_offset);
137
138 void __timecompare_update(struct timecompare *sync,
139                           u64 source_tstamp)
140 {
141         s64 offset;
142         u64 average_time;
143
144         if (!timecompare_offset(sync, &offset, &average_time))
145                 return;
146
147         if (!sync->last_update) {
148                 sync->last_update = average_time;
149                 sync->offset = offset;
150                 sync->skew = 0;
151         } else {
152                 s64 delta_nsec = average_time - sync->last_update;
153
154                 /* avoid division by negative or small deltas */
155                 if (delta_nsec >= 10000) {
156                         s64 delta_offset_nsec = offset - sync->offset;
157                         s64 skew; /* delta_offset_nsec *
158                                      TIMECOMPARE_SKEW_RESOLUTION /
159                                      delta_nsec */
160                         u64 divisor;
161
162                         /* div_s64() is limited to 32 bit divisor */
163                         skew = delta_offset_nsec * TIMECOMPARE_SKEW_RESOLUTION;
164                         divisor = delta_nsec;
165                         while (unlikely(divisor >= ((s64)1) << 32)) {
166                                 /* divide both by 2; beware, right shift
167                                    of negative value has undefined
168                                    behavior and can only be used for
169                                    the positive divisor */
170                                 skew = div_s64(skew, 2);
171                                 divisor >>= 1;
172                         }
173                         skew = div_s64(skew, divisor);
174
175                         /*
176                          * Calculate new overall skew as 4/16 the
177                          * old value and 12/16 the new one. This is
178                          * a rather arbitrary tradeoff between
179                          * only using the latest measurement (0/16 and
180                          * 16/16) and even more weight on past measurements.
181                          */
182 #define TIMECOMPARE_NEW_SKEW_PER_16 12
183                         sync->skew =
184                                 div_s64((16 - TIMECOMPARE_NEW_SKEW_PER_16) *
185                                         sync->skew +
186                                         TIMECOMPARE_NEW_SKEW_PER_16 * skew,
187                                         16);
188                         sync->last_update = average_time;
189                         sync->offset = offset;
190                 }
191         }
192 }
193 EXPORT_SYMBOL_GPL(__timecompare_update);