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 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 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 } 177 178 void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const, 179 const struct can_bittiming *dbt, 180 u32 *ctrlmode, u32 ctrlmode_supported) 181 182 { 183 if (!tdc_const || !(ctrlmode_supported & CAN_CTRLMODE_TDC_AUTO)) 184 return; 185 186 *ctrlmode &= ~CAN_CTRLMODE_TDC_MASK; 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 /* Sample point in clock periods */ 194 u32 sample_point_in_tc = (CAN_SYNC_SEG + dbt->prop_seg + 195 dbt->phase_seg1) * dbt->brp; 196 197 if (sample_point_in_tc < tdc_const->tdco_min) 198 return; 199 tdc->tdco = min(sample_point_in_tc, tdc_const->tdco_max); 200 *ctrlmode |= CAN_CTRLMODE_TDC_AUTO; 201 } 202 } 203 #endif /* CONFIG_CAN_CALC_BITTIMING */ 204 205 /* Checks the validity of the specified bit-timing parameters prop_seg, 206 * phase_seg1, phase_seg2 and sjw and tries to determine the bitrate 207 * prescaler value brp. You can find more information in the header 208 * file linux/can/netlink.h. 209 */ 210 static int can_fixup_bittiming(struct net_device *dev, struct can_bittiming *bt, 211 const struct can_bittiming_const *btc) 212 { 213 struct can_priv *priv = netdev_priv(dev); 214 unsigned int tseg1, alltseg; 215 u64 brp64; 216 217 tseg1 = bt->prop_seg + bt->phase_seg1; 218 if (!bt->sjw) 219 bt->sjw = 1; 220 if (bt->sjw > btc->sjw_max || 221 tseg1 < btc->tseg1_min || tseg1 > btc->tseg1_max || 222 bt->phase_seg2 < btc->tseg2_min || bt->phase_seg2 > btc->tseg2_max) 223 return -ERANGE; 224 225 brp64 = (u64)priv->clock.freq * (u64)bt->tq; 226 if (btc->brp_inc > 1) 227 do_div(brp64, btc->brp_inc); 228 brp64 += 500000000UL - 1; 229 do_div(brp64, 1000000000UL); /* the practicable BRP */ 230 if (btc->brp_inc > 1) 231 brp64 *= btc->brp_inc; 232 bt->brp = (u32)brp64; 233 234 if (bt->brp < btc->brp_min || bt->brp > btc->brp_max) 235 return -EINVAL; 236 237 alltseg = bt->prop_seg + bt->phase_seg1 + bt->phase_seg2 + 1; 238 bt->bitrate = priv->clock.freq / (bt->brp * alltseg); 239 bt->sample_point = ((tseg1 + 1) * 1000) / alltseg; 240 241 return 0; 242 } 243 244 /* Checks the validity of predefined bitrate settings */ 245 static int 246 can_validate_bitrate(struct net_device *dev, struct can_bittiming *bt, 247 const u32 *bitrate_const, 248 const unsigned int bitrate_const_cnt) 249 { 250 struct can_priv *priv = netdev_priv(dev); 251 unsigned int i; 252 253 for (i = 0; i < bitrate_const_cnt; i++) { 254 if (bt->bitrate == bitrate_const[i]) 255 break; 256 } 257 258 if (i >= priv->bitrate_const_cnt) 259 return -EINVAL; 260 261 return 0; 262 } 263 264 int can_get_bittiming(struct net_device *dev, struct can_bittiming *bt, 265 const struct can_bittiming_const *btc, 266 const u32 *bitrate_const, 267 const unsigned int bitrate_const_cnt) 268 { 269 int err; 270 271 /* Depending on the given can_bittiming parameter structure the CAN 272 * timing parameters are calculated based on the provided bitrate OR 273 * alternatively the CAN timing parameters (tq, prop_seg, etc.) are 274 * provided directly which are then checked and fixed up. 275 */ 276 if (!bt->tq && bt->bitrate && btc) 277 err = can_calc_bittiming(dev, bt, btc); 278 else if (bt->tq && !bt->bitrate && btc) 279 err = can_fixup_bittiming(dev, bt, btc); 280 else if (!bt->tq && bt->bitrate && bitrate_const) 281 err = can_validate_bitrate(dev, bt, bitrate_const, 282 bitrate_const_cnt); 283 else 284 err = -EINVAL; 285 286 return err; 287 } 288