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 #ifdef CONFIG_CAN_CALC_BITTIMING
11 #define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */
12
13 /* Bit-timing calculation derived from:
14 *
15 * Code based on LinCAN sources and H8S2638 project
16 * Copyright 2004-2006 Pavel Pisa - DCE FELK CVUT cz
17 * Copyright 2005 Stanislav Marek
18 * email: pisa@cmp.felk.cvut.cz
19 *
20 * Calculates proper bit-timing parameters for a specified bit-rate
21 * and sample-point, which can then be used to set the bit-timing
22 * registers of the CAN controller. You can find more information
23 * in the header file linux/can/netlink.h.
24 */
25 static int
can_update_sample_point(const struct can_bittiming_const * btc,const unsigned int sample_point_nominal,const unsigned int tseg,unsigned int * tseg1_ptr,unsigned int * tseg2_ptr,unsigned int * sample_point_error_ptr)26 can_update_sample_point(const struct can_bittiming_const *btc,
27 const unsigned int sample_point_nominal, const unsigned int tseg,
28 unsigned int *tseg1_ptr, unsigned int *tseg2_ptr,
29 unsigned int *sample_point_error_ptr)
30 {
31 unsigned int sample_point_error, best_sample_point_error = UINT_MAX;
32 unsigned int sample_point, best_sample_point = 0;
33 unsigned int tseg1, tseg2;
34 int i;
35
36 for (i = 0; i <= 1; i++) {
37 tseg2 = tseg + CAN_SYNC_SEG -
38 (sample_point_nominal * (tseg + CAN_SYNC_SEG)) /
39 1000 - i;
40 tseg2 = clamp(tseg2, btc->tseg2_min, btc->tseg2_max);
41 tseg1 = tseg - tseg2;
42 if (tseg1 > btc->tseg1_max) {
43 tseg1 = btc->tseg1_max;
44 tseg2 = tseg - tseg1;
45 }
46
47 sample_point = 1000 * (tseg + CAN_SYNC_SEG - tseg2) /
48 (tseg + CAN_SYNC_SEG);
49 sample_point_error = abs(sample_point_nominal - sample_point);
50
51 if (sample_point <= sample_point_nominal &&
52 sample_point_error < best_sample_point_error) {
53 best_sample_point = sample_point;
54 best_sample_point_error = sample_point_error;
55 *tseg1_ptr = tseg1;
56 *tseg2_ptr = tseg2;
57 }
58 }
59
60 if (sample_point_error_ptr)
61 *sample_point_error_ptr = best_sample_point_error;
62
63 return best_sample_point;
64 }
65
can_calc_bittiming(const struct net_device * dev,struct can_bittiming * bt,const struct can_bittiming_const * btc)66 int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
67 const struct can_bittiming_const *btc)
68 {
69 struct can_priv *priv = netdev_priv(dev);
70 unsigned int bitrate; /* current bitrate */
71 unsigned int bitrate_error; /* difference between current and nominal value */
72 unsigned int best_bitrate_error = UINT_MAX;
73 unsigned int sample_point_error; /* difference between current and nominal value */
74 unsigned int best_sample_point_error = UINT_MAX;
75 unsigned int sample_point_nominal; /* nominal sample point */
76 unsigned int best_tseg = 0; /* current best value for tseg */
77 unsigned int best_brp = 0; /* current best value for brp */
78 unsigned int brp, tsegall, tseg, tseg1 = 0, tseg2 = 0;
79 u64 v64;
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 netdev_err(dev,
138 "bitrate error %d.%d%% too high\n",
139 bitrate_error / 10, bitrate_error % 10);
140 return -EDOM;
141 }
142 netdev_warn(dev, "bitrate error %d.%d%%\n",
143 bitrate_error / 10, bitrate_error % 10);
144 }
145
146 /* real sample point */
147 bt->sample_point = can_update_sample_point(btc, sample_point_nominal,
148 best_tseg, &tseg1, &tseg2,
149 NULL);
150
151 v64 = (u64)best_brp * 1000 * 1000 * 1000;
152 do_div(v64, priv->clock.freq);
153 bt->tq = (u32)v64;
154 bt->prop_seg = tseg1 / 2;
155 bt->phase_seg1 = tseg1 - bt->prop_seg;
156 bt->phase_seg2 = tseg2;
157
158 /* check for sjw user settings */
159 if (!bt->sjw || !btc->sjw_max) {
160 bt->sjw = 1;
161 } else {
162 /* bt->sjw is at least 1 -> sanitize upper bound to sjw_max */
163 if (bt->sjw > btc->sjw_max)
164 bt->sjw = btc->sjw_max;
165 /* bt->sjw must not be higher than tseg2 */
166 if (tseg2 < bt->sjw)
167 bt->sjw = tseg2;
168 }
169
170 bt->brp = best_brp;
171
172 /* real bitrate */
173 bt->bitrate = priv->clock.freq /
174 (bt->brp * (CAN_SYNC_SEG + tseg1 + tseg2));
175
176 return 0;
177 }
178
can_calc_tdco(struct can_tdc * tdc,const struct can_tdc_const * tdc_const,const struct can_bittiming * dbt,u32 * ctrlmode,u32 ctrlmode_supported)179 void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
180 const struct can_bittiming *dbt,
181 u32 *ctrlmode, u32 ctrlmode_supported)
182
183 {
184 if (!tdc_const || !(ctrlmode_supported & CAN_CTRLMODE_TDC_AUTO))
185 return;
186
187 *ctrlmode &= ~CAN_CTRLMODE_TDC_MASK;
188
189 /* As specified in ISO 11898-1 section 11.3.3 "Transmitter
190 * delay compensation" (TDC) is only applicable if data BRP is
191 * one or two.
192 */
193 if (dbt->brp == 1 || dbt->brp == 2) {
194 /* Sample point in clock periods */
195 u32 sample_point_in_tc = (CAN_SYNC_SEG + dbt->prop_seg +
196 dbt->phase_seg1) * dbt->brp;
197
198 if (sample_point_in_tc < tdc_const->tdco_min)
199 return;
200 tdc->tdco = min(sample_point_in_tc, tdc_const->tdco_max);
201 *ctrlmode |= CAN_CTRLMODE_TDC_AUTO;
202 }
203 }
204 #endif /* CONFIG_CAN_CALC_BITTIMING */
205
206 /* Checks the validity of the specified bit-timing parameters prop_seg,
207 * phase_seg1, phase_seg2 and sjw and tries to determine the bitrate
208 * prescaler value brp. You can find more information in the header
209 * file linux/can/netlink.h.
210 */
can_fixup_bittiming(const struct net_device * dev,struct can_bittiming * bt,const struct can_bittiming_const * btc)211 static int can_fixup_bittiming(const struct net_device *dev, struct can_bittiming *bt,
212 const struct can_bittiming_const *btc)
213 {
214 const struct can_priv *priv = netdev_priv(dev);
215 unsigned int tseg1, alltseg;
216 u64 brp64;
217
218 tseg1 = bt->prop_seg + bt->phase_seg1;
219 if (!bt->sjw)
220 bt->sjw = 1;
221 if (bt->sjw > btc->sjw_max ||
222 tseg1 < btc->tseg1_min || tseg1 > btc->tseg1_max ||
223 bt->phase_seg2 < btc->tseg2_min || bt->phase_seg2 > btc->tseg2_max)
224 return -ERANGE;
225
226 brp64 = (u64)priv->clock.freq * (u64)bt->tq;
227 if (btc->brp_inc > 1)
228 do_div(brp64, btc->brp_inc);
229 brp64 += 500000000UL - 1;
230 do_div(brp64, 1000000000UL); /* the practicable BRP */
231 if (btc->brp_inc > 1)
232 brp64 *= btc->brp_inc;
233 bt->brp = (u32)brp64;
234
235 if (bt->brp < btc->brp_min || bt->brp > btc->brp_max)
236 return -EINVAL;
237
238 alltseg = bt->prop_seg + bt->phase_seg1 + bt->phase_seg2 + 1;
239 bt->bitrate = priv->clock.freq / (bt->brp * alltseg);
240 bt->sample_point = ((tseg1 + 1) * 1000) / alltseg;
241
242 return 0;
243 }
244
245 /* Checks the validity of predefined bitrate settings */
246 static int
can_validate_bitrate(const struct net_device * dev,const struct can_bittiming * bt,const u32 * bitrate_const,const unsigned int bitrate_const_cnt)247 can_validate_bitrate(const struct net_device *dev, const struct can_bittiming *bt,
248 const u32 *bitrate_const,
249 const unsigned int bitrate_const_cnt)
250 {
251 unsigned int i;
252
253 for (i = 0; i < bitrate_const_cnt; i++) {
254 if (bt->bitrate == bitrate_const[i])
255 return 0;
256 }
257
258 return -EINVAL;
259 }
260
can_get_bittiming(const struct net_device * dev,struct can_bittiming * bt,const struct can_bittiming_const * btc,const u32 * bitrate_const,const unsigned int bitrate_const_cnt)261 int can_get_bittiming(const struct net_device *dev, struct can_bittiming *bt,
262 const struct can_bittiming_const *btc,
263 const u32 *bitrate_const,
264 const unsigned int bitrate_const_cnt)
265 {
266 int err;
267
268 /* Depending on the given can_bittiming parameter structure the CAN
269 * timing parameters are calculated based on the provided bitrate OR
270 * alternatively the CAN timing parameters (tq, prop_seg, etc.) are
271 * provided directly which are then checked and fixed up.
272 */
273 if (!bt->tq && bt->bitrate && btc)
274 err = can_calc_bittiming(dev, bt, btc);
275 else if (bt->tq && !bt->bitrate && btc)
276 err = can_fixup_bittiming(dev, bt, btc);
277 else if (!bt->tq && bt->bitrate && bitrate_const)
278 err = can_validate_bitrate(dev, bt, bitrate_const,
279 bitrate_const_cnt);
280 else
281 err = -EINVAL;
282
283 return err;
284 }
285