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 */ 24 static int 25 can_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 65 int 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 } 173 174 void 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 } 199