199 lines · c
1// SPDX-License-Identifier: GPL-2.0-only2/* Copyright (C) 2005 Marc Kleine-Budde, Pengutronix3 * Copyright (C) 2006 Andrey Volkov, Varma Electronics4 * 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 project15 * Copyright 2004-2006 Pavel Pisa - DCE FELK CVUT cz16 * Copyright 2005 Stanislav Marek17 * email: pisa@cmp.felk.cvut.cz18 *19 * Calculates proper bit-timing parameters for a specified bit-rate20 * and sample-point, which can then be used to set the bit-timing21 * registers of the CAN controller. You can find more information22 * in the header file linux/can/netlink.h.23 */24static int25can_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 65int 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 else90 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 174void 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 "Transmitter185 * delay compensation" (TDC) is only applicable if data BRP is186 * 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