diff options
Diffstat (limited to 'drivers/net/can/dev/calc_bittiming.c')
| -rw-r--r-- | drivers/net/can/dev/calc_bittiming.c | 202 |
1 files changed, 202 insertions, 0 deletions
diff --git a/drivers/net/can/dev/calc_bittiming.c b/drivers/net/can/dev/calc_bittiming.c new file mode 100644 index 000000000000..d3caa040614d --- /dev/null +++ b/drivers/net/can/dev/calc_bittiming.c @@ -0,0 +1,202 @@ +// 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 <wg@grandegger.com> + */ + +#include <linux/units.h> +#include <linux/can/dev.h> + +#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, + const unsigned int sample_point_nominal, const 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(const 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 * KILO /* BPS */) + sample_point_nominal = 750; + else if (bt->bitrate > 500 * KILO /* BPS */) + 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 can_tdc *tdc, const struct can_tdc_const *tdc_const, + const struct can_bittiming *dbt, + u32 *ctrlmode, u32 ctrlmode_supported) + +{ + if (!tdc_const || !(ctrlmode_supported & CAN_CTRLMODE_TDC_AUTO)) + return; + + *ctrlmode &= ~CAN_CTRLMODE_TDC_MASK; + + /* 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) { + /* Sample point in clock periods */ + u32 sample_point_in_tc = (CAN_SYNC_SEG + dbt->prop_seg + + dbt->phase_seg1) * dbt->brp; + + if (sample_point_in_tc < tdc_const->tdco_min) + return; + tdc->tdco = min(sample_point_in_tc, tdc_const->tdco_max); + *ctrlmode |= CAN_CTRLMODE_TDC_AUTO; + } +} |