// SPDX-License-Identifier: GPL-2.0-only /* Copyright (C) 2005 Marc Kleine-Budde, Pengutronix * Copyright (C) 2006 Andrey Volkov, Varma Electronics * Copyright (C) 2008-2009 Wolfgang Grandegger */ #include #ifdef CONFIG_CAN_CALC_BITTIMING #define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */ /* Bit-timing calculation derived from: * * Code based on LinCAN sources and H8S2638 project * Copyright 2004-2006 Pavel Pisa - DCE FELK CVUT cz * Copyright 2005 Stanislav Marek * email: pisa@cmp.felk.cvut.cz * * Calculates proper bit-timing parameters for a specified bit-rate * and sample-point, which can then be used to set the bit-timing * registers of the CAN controller. You can find more information * in the header file linux/can/netlink.h. */ static int can_update_sample_point(const struct can_bittiming_const *btc, unsigned int sample_point_nominal, unsigned int tseg, unsigned int *tseg1_ptr, unsigned int *tseg2_ptr, unsigned int *sample_point_error_ptr) { unsigned int sample_point_error, best_sample_point_error = UINT_MAX; unsigned int sample_point, best_sample_point = 0; unsigned int tseg1, tseg2; int i; for (i = 0; i <= 1; i++) { tseg2 = tseg + CAN_SYNC_SEG - (sample_point_nominal * (tseg + CAN_SYNC_SEG)) / 1000 - i; tseg2 = clamp(tseg2, btc->tseg2_min, btc->tseg2_max); tseg1 = tseg - tseg2; if (tseg1 > btc->tseg1_max) { tseg1 = btc->tseg1_max; tseg2 = tseg - tseg1; } sample_point = 1000 * (tseg + CAN_SYNC_SEG - tseg2) / (tseg + CAN_SYNC_SEG); sample_point_error = abs(sample_point_nominal - sample_point); if (sample_point <= sample_point_nominal && sample_point_error < best_sample_point_error) { best_sample_point = sample_point; best_sample_point_error = sample_point_error; *tseg1_ptr = tseg1; *tseg2_ptr = tseg2; } } if (sample_point_error_ptr) *sample_point_error_ptr = best_sample_point_error; return best_sample_point; } int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt, const struct can_bittiming_const *btc) { struct can_priv *priv = netdev_priv(dev); unsigned int bitrate; /* current bitrate */ unsigned int bitrate_error; /* difference between current and nominal value */ unsigned int best_bitrate_error = UINT_MAX; unsigned int sample_point_error; /* difference between current and nominal value */ unsigned int best_sample_point_error = UINT_MAX; unsigned int sample_point_nominal; /* nominal sample point */ unsigned int best_tseg = 0; /* current best value for tseg */ unsigned int best_brp = 0; /* current best value for brp */ unsigned int brp, tsegall, tseg, tseg1 = 0, tseg2 = 0; u64 v64; /* Use CiA recommended sample points */ if (bt->sample_point) { sample_point_nominal = bt->sample_point; } else { if (bt->bitrate > 800 * CAN_KBPS) sample_point_nominal = 750; else if (bt->bitrate > 500 * CAN_KBPS) sample_point_nominal = 800; else sample_point_nominal = 875; } /* tseg even = round down, odd = round up */ for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1; tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) { tsegall = CAN_SYNC_SEG + tseg / 2; /* Compute all possible tseg choices (tseg=tseg1+tseg2) */ brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2; /* choose brp step which is possible in system */ brp = (brp / btc->brp_inc) * btc->brp_inc; if (brp < btc->brp_min || brp > btc->brp_max) continue; bitrate = priv->clock.freq / (brp * tsegall); bitrate_error = abs(bt->bitrate - bitrate); /* tseg brp biterror */ if (bitrate_error > best_bitrate_error) continue; /* reset sample point error if we have a better bitrate */ if (bitrate_error < best_bitrate_error) best_sample_point_error = UINT_MAX; can_update_sample_point(btc, sample_point_nominal, tseg / 2, &tseg1, &tseg2, &sample_point_error); if (sample_point_error > best_sample_point_error) continue; best_sample_point_error = sample_point_error; best_bitrate_error = bitrate_error; best_tseg = tseg / 2; best_brp = brp; if (bitrate_error == 0 && sample_point_error == 0) break; } if (best_bitrate_error) { /* Error in one-tenth of a percent */ v64 = (u64)best_bitrate_error * 1000; do_div(v64, bt->bitrate); bitrate_error = (u32)v64; if (bitrate_error > CAN_CALC_MAX_ERROR) { netdev_err(dev, "bitrate error %d.%d%% too high\n", bitrate_error / 10, bitrate_error % 10); return -EDOM; } netdev_warn(dev, "bitrate error %d.%d%%\n", bitrate_error / 10, bitrate_error % 10); } /* real sample point */ bt->sample_point = can_update_sample_point(btc, sample_point_nominal, best_tseg, &tseg1, &tseg2, NULL); v64 = (u64)best_brp * 1000 * 1000 * 1000; do_div(v64, priv->clock.freq); bt->tq = (u32)v64; bt->prop_seg = tseg1 / 2; bt->phase_seg1 = tseg1 - bt->prop_seg; bt->phase_seg2 = tseg2; /* check for sjw user settings */ if (!bt->sjw || !btc->sjw_max) { bt->sjw = 1; } else { /* bt->sjw is at least 1 -> sanitize upper bound to sjw_max */ if (bt->sjw > btc->sjw_max) bt->sjw = btc->sjw_max; /* bt->sjw must not be higher than tseg2 */ if (tseg2 < bt->sjw) bt->sjw = tseg2; } bt->brp = best_brp; /* real bitrate */ bt->bitrate = priv->clock.freq / (bt->brp * (CAN_SYNC_SEG + tseg1 + tseg2)); return 0; } void can_calc_tdco(struct net_device *dev) { struct can_priv *priv = netdev_priv(dev); const struct can_bittiming *dbt = &priv->data_bittiming; struct can_tdc *tdc = &priv->tdc; const struct can_tdc_const *tdc_const = priv->tdc_const; if (!tdc_const) return; /* As specified in ISO 11898-1 section 11.3.3 "Transmitter * delay compensation" (TDC) is only applicable if data BRP is * one or two. */ if (dbt->brp == 1 || dbt->brp == 2) { /* Reuse "normal" sample point and convert it to time quanta */ u32 sample_point_in_tq = can_bit_time(dbt) * dbt->sample_point / 1000; tdc->tdco = min(sample_point_in_tq, tdc_const->tdco_max); } else { tdc->tdco = 0; } } #endif /* CONFIG_CAN_CALC_BITTIMING */ /* Checks the validity of the specified bit-timing parameters prop_seg, * phase_seg1, phase_seg2 and sjw and tries to determine the bitrate * prescaler value brp. You can find more information in the header * file linux/can/netlink.h. */ static int can_fixup_bittiming(struct net_device *dev, struct can_bittiming *bt, const struct can_bittiming_const *btc) { struct can_priv *priv = netdev_priv(dev); unsigned int tseg1, alltseg; u64 brp64; tseg1 = bt->prop_seg + bt->phase_seg1; if (!bt->sjw) bt->sjw = 1; if (bt->sjw > btc->sjw_max || tseg1 < btc->tseg1_min || tseg1 > btc->tseg1_max || bt->phase_seg2 < btc->tseg2_min || bt->phase_seg2 > btc->tseg2_max) return -ERANGE; brp64 = (u64)priv->clock.freq * (u64)bt->tq; if (btc->brp_inc > 1) do_div(brp64, btc->brp_inc); brp64 += 500000000UL - 1; do_div(brp64, 1000000000UL); /* the practicable BRP */ if (btc->brp_inc > 1) brp64 *= btc->brp_inc; bt->brp = (u32)brp64; if (bt->brp < btc->brp_min || bt->brp > btc->brp_max) return -EINVAL; alltseg = bt->prop_seg + bt->phase_seg1 + bt->phase_seg2 + 1; bt->bitrate = priv->clock.freq / (bt->brp * alltseg); bt->sample_point = ((tseg1 + 1) * 1000) / alltseg; return 0; } /* Checks the validity of predefined bitrate settings */ static int can_validate_bitrate(struct net_device *dev, struct can_bittiming *bt, const u32 *bitrate_const, const unsigned int bitrate_const_cnt) { struct can_priv *priv = netdev_priv(dev); unsigned int i; for (i = 0; i < bitrate_const_cnt; i++) { if (bt->bitrate == bitrate_const[i]) break; } if (i >= priv->bitrate_const_cnt) return -EINVAL; return 0; } int can_get_bittiming(struct net_device *dev, struct can_bittiming *bt, const struct can_bittiming_const *btc, const u32 *bitrate_const, const unsigned int bitrate_const_cnt) { int err; /* Depending on the given can_bittiming parameter structure the CAN * timing parameters are calculated based on the provided bitrate OR * alternatively the CAN timing parameters (tq, prop_seg, etc.) are * provided directly which are then checked and fixed up. */ if (!bt->tq && bt->bitrate && btc) err = can_calc_bittiming(dev, bt, btc); else if (bt->tq && !bt->bitrate && btc) err = can_fixup_bittiming(dev, bt, btc); else if (!bt->tq && bt->bitrate && bitrate_const) err = can_validate_bitrate(dev, bt, bitrate_const, bitrate_const_cnt); else err = -EINVAL; return err; }