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 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 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 } 178 179 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 */ 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 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 } 260 261 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