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/can/dev.h>
8
9 #ifdef CONFIG_CAN_CALC_BITTIMING
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 */
24 static int
can_update_sample_point(const struct can_bittiming_const * btc,unsigned int sample_point_nominal,unsigned int tseg,unsigned int * tseg1_ptr,unsigned int * tseg2_ptr,unsigned int * sample_point_error_ptr)25 can_update_sample_point(const struct can_bittiming_const *btc,
26 unsigned int sample_point_nominal, 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
can_calc_bittiming(struct net_device * dev,struct can_bittiming * bt,const struct can_bittiming_const * btc)65 int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt,
66 const struct can_bittiming_const *btc)
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
80 /* Use CiA recommended sample points */
81 if (bt->sample_point) {
82 sample_point_nominal = bt->sample_point;
83 } else {
84 if (bt->bitrate > 800 * CAN_KBPS)
85 sample_point_nominal = 750;
86 else if (bt->bitrate > 500 * CAN_KBPS)
87 sample_point_nominal = 800;
88 else
89 sample_point_nominal = 875;
90 }
91
92 /* tseg even = round down, odd = round up */
93 for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1;
94 tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) {
95 tsegall = CAN_SYNC_SEG + tseg / 2;
96
97 /* Compute all possible tseg choices (tseg=tseg1+tseg2) */
98 brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2;
99
100 /* choose brp step which is possible in system */
101 brp = (brp / btc->brp_inc) * btc->brp_inc;
102 if (brp < btc->brp_min || brp > btc->brp_max)
103 continue;
104
105 bitrate = priv->clock.freq / (brp * tsegall);
106 bitrate_error = abs(bt->bitrate - bitrate);
107
108 /* tseg brp biterror */
109 if (bitrate_error > best_bitrate_error)
110 continue;
111
112 /* reset sample point error if we have a better bitrate */
113 if (bitrate_error < best_bitrate_error)
114 best_sample_point_error = UINT_MAX;
115
116 can_update_sample_point(btc, sample_point_nominal, tseg / 2,
117 &tseg1, &tseg2, &sample_point_error);
118 if (sample_point_error > best_sample_point_error)
119 continue;
120
121 best_sample_point_error = sample_point_error;
122 best_bitrate_error = bitrate_error;
123 best_tseg = tseg / 2;
124 best_brp = brp;
125
126 if (bitrate_error == 0 && sample_point_error == 0)
127 break;
128 }
129
130 if (best_bitrate_error) {
131 /* Error in one-tenth of a percent */
132 v64 = (u64)best_bitrate_error * 1000;
133 do_div(v64, bt->bitrate);
134 bitrate_error = (u32)v64;
135 if (bitrate_error > CAN_CALC_MAX_ERROR) {
136 netdev_err(dev,
137 "bitrate error %d.%d%% too high\n",
138 bitrate_error / 10, bitrate_error % 10);
139 return -EDOM;
140 }
141 netdev_warn(dev, "bitrate error %d.%d%%\n",
142 bitrate_error / 10, bitrate_error % 10);
143 }
144
145 /* real sample point */
146 bt->sample_point = can_update_sample_point(btc, sample_point_nominal,
147 best_tseg, &tseg1, &tseg2,
148 NULL);
149
150 v64 = (u64)best_brp * 1000 * 1000 * 1000;
151 do_div(v64, priv->clock.freq);
152 bt->tq = (u32)v64;
153 bt->prop_seg = tseg1 / 2;
154 bt->phase_seg1 = tseg1 - bt->prop_seg;
155 bt->phase_seg2 = tseg2;
156
157 /* check for sjw user settings */
158 if (!bt->sjw || !btc->sjw_max) {
159 bt->sjw = 1;
160 } else {
161 /* bt->sjw is at least 1 -> sanitize upper bound to sjw_max */
162 if (bt->sjw > btc->sjw_max)
163 bt->sjw = btc->sjw_max;
164 /* bt->sjw must not be higher than tseg2 */
165 if (tseg2 < bt->sjw)
166 bt->sjw = tseg2;
167 }
168
169 bt->brp = best_brp;
170
171 /* real bitrate */
172 bt->bitrate = priv->clock.freq /
173 (bt->brp * (CAN_SYNC_SEG + tseg1 + tseg2));
174
175 return 0;
176 }
177
can_calc_tdco(struct net_device * dev)178 void can_calc_tdco(struct net_device *dev)
179 {
180 struct can_priv *priv = netdev_priv(dev);
181 const struct can_bittiming *dbt = &priv->data_bittiming;
182 struct can_tdc *tdc = &priv->tdc;
183 const struct can_tdc_const *tdc_const = priv->tdc_const;
184
185 if (!tdc_const)
186 return;
187
188 /* As specified in ISO 11898-1 section 11.3.3 "Transmitter
189 * delay compensation" (TDC) is only applicable if data BRP is
190 * one or two.
191 */
192 if (dbt->brp == 1 || dbt->brp == 2) {
193 /* Reuse "normal" sample point and convert it to time quanta */
194 u32 sample_point_in_tq = can_bit_time(dbt) * dbt->sample_point / 1000;
195
196 tdc->tdco = min(sample_point_in_tq, tdc_const->tdco_max);
197 } else {
198 tdc->tdco = 0;
199 }
200 }
201 #endif /* CONFIG_CAN_CALC_BITTIMING */
202
203 /* Checks the validity of the specified bit-timing parameters prop_seg,
204 * phase_seg1, phase_seg2 and sjw and tries to determine the bitrate
205 * prescaler value brp. You can find more information in the header
206 * file linux/can/netlink.h.
207 */
can_fixup_bittiming(struct net_device * dev,struct can_bittiming * bt,const struct can_bittiming_const * btc)208 static int can_fixup_bittiming(struct net_device *dev, struct can_bittiming *bt,
209 const struct can_bittiming_const *btc)
210 {
211 struct can_priv *priv = netdev_priv(dev);
212 int tseg1, alltseg;
213 u64 brp64;
214
215 tseg1 = bt->prop_seg + bt->phase_seg1;
216 if (!bt->sjw)
217 bt->sjw = 1;
218 if (bt->sjw > btc->sjw_max ||
219 tseg1 < btc->tseg1_min || tseg1 > btc->tseg1_max ||
220 bt->phase_seg2 < btc->tseg2_min || bt->phase_seg2 > btc->tseg2_max)
221 return -ERANGE;
222
223 brp64 = (u64)priv->clock.freq * (u64)bt->tq;
224 if (btc->brp_inc > 1)
225 do_div(brp64, btc->brp_inc);
226 brp64 += 500000000UL - 1;
227 do_div(brp64, 1000000000UL); /* the practicable BRP */
228 if (btc->brp_inc > 1)
229 brp64 *= btc->brp_inc;
230 bt->brp = (u32)brp64;
231
232 if (bt->brp < btc->brp_min || bt->brp > btc->brp_max)
233 return -EINVAL;
234
235 alltseg = bt->prop_seg + bt->phase_seg1 + bt->phase_seg2 + 1;
236 bt->bitrate = priv->clock.freq / (bt->brp * alltseg);
237 bt->sample_point = ((tseg1 + 1) * 1000) / alltseg;
238
239 return 0;
240 }
241
242 /* Checks the validity of predefined bitrate settings */
243 static int
can_validate_bitrate(struct net_device * dev,struct can_bittiming * bt,const u32 * bitrate_const,const unsigned int bitrate_const_cnt)244 can_validate_bitrate(struct net_device *dev, struct can_bittiming *bt,
245 const u32 *bitrate_const,
246 const unsigned int bitrate_const_cnt)
247 {
248 struct can_priv *priv = netdev_priv(dev);
249 unsigned int i;
250
251 for (i = 0; i < bitrate_const_cnt; i++) {
252 if (bt->bitrate == bitrate_const[i])
253 break;
254 }
255
256 if (i >= priv->bitrate_const_cnt)
257 return -EINVAL;
258
259 return 0;
260 }
261
can_get_bittiming(struct net_device * dev,struct can_bittiming * bt,const struct can_bittiming_const * btc,const u32 * bitrate_const,const unsigned int bitrate_const_cnt)262 int can_get_bittiming(struct net_device *dev, struct can_bittiming *bt,
263 const struct can_bittiming_const *btc,
264 const u32 *bitrate_const,
265 const unsigned int bitrate_const_cnt)
266 {
267 int err;
268
269 /* Depending on the given can_bittiming parameter structure the CAN
270 * timing parameters are calculated based on the provided bitrate OR
271 * alternatively the CAN timing parameters (tq, prop_seg, etc.) are
272 * provided directly which are then checked and fixed up.
273 */
274 if (!bt->tq && bt->bitrate && btc)
275 err = can_calc_bittiming(dev, bt, btc);
276 else if (bt->tq && !bt->bitrate && btc)
277 err = can_fixup_bittiming(dev, bt, btc);
278 else if (!bt->tq && bt->bitrate && bitrate_const)
279 err = can_validate_bitrate(dev, bt, bitrate_const,
280 bitrate_const_cnt);
281 else
282 err = -EINVAL;
283
284 return err;
285 }
286
