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1// SPDX-License-Identifier: GPL-2.0-only
2/* Copyright (C) 2005 Marc Kleine-Budde, Pengutronix
3 * Copyright (C) 2006 Andrey Volkov, Varma Electronics
4 * Copyright (C) 2008-2009 Wolfgang Grandegger <wg@grandegger.com>
5 */
6
7#include <linux/units.h>
8#include <linux/can/dev.h>
9
10#define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */
11
12/* Bit-timing calculation derived from:
13 *
14 * Code based on LinCAN sources and H8S2638 project
15 * Copyright 2004-2006 Pavel Pisa - DCE FELK CVUT cz
16 * Copyright 2005 Stanislav Marek
17 * email: pisa@cmp.felk.cvut.cz
18 *
19 * Calculates proper bit-timing parameters for a specified bit-rate
20 * and sample-point, which can then be used to set the bit-timing
21 * registers of the CAN controller. You can find more information
22 * in the header file linux/can/netlink.h.
23 */
24static int
25can_update_sample_point(const struct can_bittiming_const *btc,
26 const unsigned int sample_point_nominal, const unsigned int tseg,
27 unsigned int *tseg1_ptr, unsigned int *tseg2_ptr,
28 unsigned int *sample_point_error_ptr)
29{
30 unsigned int sample_point_error, best_sample_point_error = UINT_MAX;
31 unsigned int sample_point, best_sample_point = 0;
32 unsigned int tseg1, tseg2;
33 int i;
34
35 for (i = 0; i <= 1; i++) {
36 tseg2 = tseg + CAN_SYNC_SEG -
37 (sample_point_nominal * (tseg + CAN_SYNC_SEG)) /
38 1000 - i;
39 tseg2 = clamp(tseg2, btc->tseg2_min, btc->tseg2_max);
40 tseg1 = tseg - tseg2;
41 if (tseg1 > btc->tseg1_max) {
42 tseg1 = btc->tseg1_max;
43 tseg2 = tseg - tseg1;
44 }
45
46 sample_point = 1000 * (tseg + CAN_SYNC_SEG - tseg2) /
47 (tseg + CAN_SYNC_SEG);
48 sample_point_error = abs(sample_point_nominal - sample_point);
49
50 if (sample_point <= sample_point_nominal &&
51 sample_point_error < best_sample_point_error) {
52 best_sample_point = sample_point;
53 best_sample_point_error = sample_point_error;
54 *tseg1_ptr = tseg1;
55 *tseg2_ptr = tseg2;
56 }
57 }
58
59 if (sample_point_error_ptr)
60 *sample_point_error_ptr = best_sample_point_error;
61
62 return best_sample_point;
63}
64
65int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
66 const struct can_bittiming_const *btc, struct netlink_ext_ack *extack)
67{
68 struct can_priv *priv = netdev_priv(dev);
69 unsigned int bitrate; /* current bitrate */
70 unsigned int bitrate_error; /* difference between current and nominal value */
71 unsigned int best_bitrate_error = UINT_MAX;
72 unsigned int sample_point_error; /* difference between current and nominal value */
73 unsigned int best_sample_point_error = UINT_MAX;
74 unsigned int sample_point_nominal; /* nominal sample point */
75 unsigned int best_tseg = 0; /* current best value for tseg */
76 unsigned int best_brp = 0; /* current best value for brp */
77 unsigned int brp, tsegall, tseg, tseg1 = 0, tseg2 = 0;
78 u64 v64;
79 int err;
80
81 /* Use CiA recommended sample points */
82 if (bt->sample_point) {
83 sample_point_nominal = bt->sample_point;
84 } else {
85 if (bt->bitrate > 800 * KILO /* BPS */)
86 sample_point_nominal = 750;
87 else if (bt->bitrate > 500 * KILO /* BPS */)
88 sample_point_nominal = 800;
89 else
90 sample_point_nominal = 875;
91 }
92
93 /* tseg even = round down, odd = round up */
94 for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1;
95 tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) {
96 tsegall = CAN_SYNC_SEG + tseg / 2;
97
98 /* Compute all possible tseg choices (tseg=tseg1+tseg2) */
99 brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2;
100
101 /* choose brp step which is possible in system */
102 brp = (brp / btc->brp_inc) * btc->brp_inc;
103 if (brp < btc->brp_min || brp > btc->brp_max)
104 continue;
105
106 bitrate = priv->clock.freq / (brp * tsegall);
107 bitrate_error = abs(bt->bitrate - bitrate);
108
109 /* tseg brp biterror */
110 if (bitrate_error > best_bitrate_error)
111 continue;
112
113 /* reset sample point error if we have a better bitrate */
114 if (bitrate_error < best_bitrate_error)
115 best_sample_point_error = UINT_MAX;
116
117 can_update_sample_point(btc, sample_point_nominal, tseg / 2,
118 &tseg1, &tseg2, &sample_point_error);
119 if (sample_point_error >= best_sample_point_error)
120 continue;
121
122 best_sample_point_error = sample_point_error;
123 best_bitrate_error = bitrate_error;
124 best_tseg = tseg / 2;
125 best_brp = brp;
126
127 if (bitrate_error == 0 && sample_point_error == 0)
128 break;
129 }
130
131 if (best_bitrate_error) {
132 /* Error in one-tenth of a percent */
133 v64 = (u64)best_bitrate_error * 1000;
134 do_div(v64, bt->bitrate);
135 bitrate_error = (u32)v64;
136 if (bitrate_error > CAN_CALC_MAX_ERROR) {
137 NL_SET_ERR_MSG_FMT(extack,
138 "bitrate error: %u.%u%% too high",
139 bitrate_error / 10, bitrate_error % 10);
140 return -EINVAL;
141 }
142 NL_SET_ERR_MSG_FMT(extack,
143 "bitrate error: %u.%u%%",
144 bitrate_error / 10, bitrate_error % 10);
145 }
146
147 /* real sample point */
148 bt->sample_point = can_update_sample_point(btc, sample_point_nominal,
149 best_tseg, &tseg1, &tseg2,
150 NULL);
151
152 v64 = (u64)best_brp * 1000 * 1000 * 1000;
153 do_div(v64, priv->clock.freq);
154 bt->tq = (u32)v64;
155 bt->prop_seg = tseg1 / 2;
156 bt->phase_seg1 = tseg1 - bt->prop_seg;
157 bt->phase_seg2 = tseg2;
158
159 can_sjw_set_default(bt);
160
161 err = can_sjw_check(dev, bt, btc, extack);
162 if (err)
163 return err;
164
165 bt->brp = best_brp;
166
167 /* real bitrate */
168 bt->bitrate = priv->clock.freq /
169 (bt->brp * can_bit_time(bt));
170
171 return 0;
172}
173
174void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
175 const struct can_bittiming *dbt,
176 u32 *ctrlmode, u32 ctrlmode_supported)
177
178{
179 if (!tdc_const || !(ctrlmode_supported & CAN_CTRLMODE_TDC_AUTO))
180 return;
181
182 *ctrlmode &= ~CAN_CTRLMODE_TDC_MASK;
183
184 /* As specified in ISO 11898-1 section 11.3.3 "Transmitter
185 * delay compensation" (TDC) is only applicable if data BRP is
186 * one or two.
187 */
188 if (dbt->brp == 1 || dbt->brp == 2) {
189 /* Sample point in clock periods */
190 u32 sample_point_in_tc = (CAN_SYNC_SEG + dbt->prop_seg +
191 dbt->phase_seg1) * dbt->brp;
192
193 if (sample_point_in_tc < tdc_const->tdco_min)
194 return;
195 tdc->tdco = min(sample_point_in_tc, tdc_const->tdco_max);
196 *ctrlmode |= CAN_CTRLMODE_TDC_AUTO;
197 }
198}
1// SPDX-License-Identifier: GPL-2.0-only
2/* Copyright (C) 2005 Marc Kleine-Budde, Pengutronix
3 * Copyright (C) 2006 Andrey Volkov, Varma Electronics
4 * Copyright (C) 2008-2009 Wolfgang Grandegger <wg@grandegger.com>
5 */
6
7#include <linux/units.h>
8#include <linux/can/dev.h>
9
10#define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */
11
12/* Bit-timing calculation derived from:
13 *
14 * Code based on LinCAN sources and H8S2638 project
15 * Copyright 2004-2006 Pavel Pisa - DCE FELK CVUT cz
16 * Copyright 2005 Stanislav Marek
17 * email: pisa@cmp.felk.cvut.cz
18 *
19 * Calculates proper bit-timing parameters for a specified bit-rate
20 * and sample-point, which can then be used to set the bit-timing
21 * registers of the CAN controller. You can find more information
22 * in the header file linux/can/netlink.h.
23 */
24static int
25can_update_sample_point(const struct can_bittiming_const *btc,
26 const unsigned int sample_point_nominal, const unsigned int tseg,
27 unsigned int *tseg1_ptr, unsigned int *tseg2_ptr,
28 unsigned int *sample_point_error_ptr)
29{
30 unsigned int sample_point_error, best_sample_point_error = UINT_MAX;
31 unsigned int sample_point, best_sample_point = 0;
32 unsigned int tseg1, tseg2;
33 int i;
34
35 for (i = 0; i <= 1; i++) {
36 tseg2 = tseg + CAN_SYNC_SEG -
37 (sample_point_nominal * (tseg + CAN_SYNC_SEG)) /
38 1000 - i;
39 tseg2 = clamp(tseg2, btc->tseg2_min, btc->tseg2_max);
40 tseg1 = tseg - tseg2;
41 if (tseg1 > btc->tseg1_max) {
42 tseg1 = btc->tseg1_max;
43 tseg2 = tseg - tseg1;
44 }
45
46 sample_point = 1000 * (tseg + CAN_SYNC_SEG - tseg2) /
47 (tseg + CAN_SYNC_SEG);
48 sample_point_error = abs(sample_point_nominal - sample_point);
49
50 if (sample_point <= sample_point_nominal &&
51 sample_point_error < best_sample_point_error) {
52 best_sample_point = sample_point;
53 best_sample_point_error = sample_point_error;
54 *tseg1_ptr = tseg1;
55 *tseg2_ptr = tseg2;
56 }
57 }
58
59 if (sample_point_error_ptr)
60 *sample_point_error_ptr = best_sample_point_error;
61
62 return best_sample_point;
63}
64
65int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
66 const struct can_bittiming_const *btc, struct netlink_ext_ack *extack)
67{
68 struct can_priv *priv = netdev_priv(dev);
69 unsigned int bitrate; /* current bitrate */
70 unsigned int bitrate_error; /* difference between current and nominal value */
71 unsigned int best_bitrate_error = UINT_MAX;
72 unsigned int sample_point_error; /* difference between current and nominal value */
73 unsigned int best_sample_point_error = UINT_MAX;
74 unsigned int sample_point_nominal; /* nominal sample point */
75 unsigned int best_tseg = 0; /* current best value for tseg */
76 unsigned int best_brp = 0; /* current best value for brp */
77 unsigned int brp, tsegall, tseg, tseg1 = 0, tseg2 = 0;
78 u64 v64;
79 int err;
80
81 /* Use CiA recommended sample points */
82 if (bt->sample_point) {
83 sample_point_nominal = bt->sample_point;
84 } else {
85 if (bt->bitrate > 800 * KILO /* BPS */)
86 sample_point_nominal = 750;
87 else if (bt->bitrate > 500 * KILO /* BPS */)
88 sample_point_nominal = 800;
89 else
90 sample_point_nominal = 875;
91 }
92
93 /* tseg even = round down, odd = round up */
94 for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1;
95 tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) {
96 tsegall = CAN_SYNC_SEG + tseg / 2;
97
98 /* Compute all possible tseg choices (tseg=tseg1+tseg2) */
99 brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2;
100
101 /* choose brp step which is possible in system */
102 brp = (brp / btc->brp_inc) * btc->brp_inc;
103 if (brp < btc->brp_min || brp > btc->brp_max)
104 continue;
105
106 bitrate = priv->clock.freq / (brp * tsegall);
107 bitrate_error = abs(bt->bitrate - bitrate);
108
109 /* tseg brp biterror */
110 if (bitrate_error > best_bitrate_error)
111 continue;
112
113 /* reset sample point error if we have a better bitrate */
114 if (bitrate_error < best_bitrate_error)
115 best_sample_point_error = UINT_MAX;
116
117 can_update_sample_point(btc, sample_point_nominal, tseg / 2,
118 &tseg1, &tseg2, &sample_point_error);
119 if (sample_point_error >= best_sample_point_error)
120 continue;
121
122 best_sample_point_error = sample_point_error;
123 best_bitrate_error = bitrate_error;
124 best_tseg = tseg / 2;
125 best_brp = brp;
126
127 if (bitrate_error == 0 && sample_point_error == 0)
128 break;
129 }
130
131 if (best_bitrate_error) {
132 /* Error in one-tenth of a percent */
133 v64 = (u64)best_bitrate_error * 1000;
134 do_div(v64, bt->bitrate);
135 bitrate_error = (u32)v64;
136 if (bitrate_error > CAN_CALC_MAX_ERROR) {
137 NL_SET_ERR_MSG_FMT(extack,
138 "bitrate error: %u.%u%% too high",
139 bitrate_error / 10, bitrate_error % 10);
140 return -EINVAL;
141 }
142 NL_SET_ERR_MSG_FMT(extack,
143 "bitrate error: %u.%u%%",
144 bitrate_error / 10, bitrate_error % 10);
145 }
146
147 /* real sample point */
148 bt->sample_point = can_update_sample_point(btc, sample_point_nominal,
149 best_tseg, &tseg1, &tseg2,
150 NULL);
151
152 v64 = (u64)best_brp * 1000 * 1000 * 1000;
153 do_div(v64, priv->clock.freq);
154 bt->tq = (u32)v64;
155 bt->prop_seg = tseg1 / 2;
156 bt->phase_seg1 = tseg1 - bt->prop_seg;
157 bt->phase_seg2 = tseg2;
158
159 can_sjw_set_default(bt);
160
161 err = can_sjw_check(dev, bt, btc, extack);
162 if (err)
163 return err;
164
165 bt->brp = best_brp;
166
167 /* real bitrate */
168 bt->bitrate = priv->clock.freq /
169 (bt->brp * can_bit_time(bt));
170
171 return 0;
172}
173
174void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
175 const struct can_bittiming *dbt,
176 u32 *ctrlmode, u32 ctrlmode_supported)
177
178{
179 if (!tdc_const || !(ctrlmode_supported & CAN_CTRLMODE_TDC_AUTO))
180 return;
181
182 *ctrlmode &= ~CAN_CTRLMODE_TDC_MASK;
183
184 /* As specified in ISO 11898-1 section 11.3.3 "Transmitter
185 * delay compensation" (TDC) is only applicable if data BRP is
186 * one or two.
187 */
188 if (dbt->brp == 1 || dbt->brp == 2) {
189 /* Sample point in clock periods */
190 u32 sample_point_in_tc = (CAN_SYNC_SEG + dbt->prop_seg +
191 dbt->phase_seg1) * dbt->brp;
192
193 if (sample_point_in_tc < tdc_const->tdco_min)
194 return;
195 tdc->tdco = min(sample_point_in_tc, tdc_const->tdco_max);
196 *ctrlmode |= CAN_CTRLMODE_TDC_AUTO;
197 }
198}