can-utils/calc-bit-timing/can-calc-bit-timing-v3_18.c

/* SPDX-License-Identifier: GPL-2.0-only */

/*
 * imported from v3.18-rc1~52^2~248^2~1
 *
 */

/*
 * Copyright (C) 2005 Marc Kleine-Budde, Pengutronix
 * Copyright (C) 2006 Andrey Volkov, Varma Electronics
 * Copyright (C) 2008-2009 Wolfgang Grandegger <wg@grandegger.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the version 2 of the GNU General Public License
 * as published by the Free Software Foundation
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, see <http://www.gnu.org/licenses/>.
 */

/*
 * 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_spt(const struct can_bittiming_const *btc,
			  int sampl_pt, int tseg, int *tseg1, int *tseg2)
{
	*tseg2 = tseg + 1 - (sampl_pt * (tseg + 1)) / 1000;
	if (*tseg2 < btc->tseg2_min)
		*tseg2 = btc->tseg2_min;
	if (*tseg2 > btc->tseg2_max)
		*tseg2 = btc->tseg2_max;
	*tseg1 = tseg - *tseg2;
	if (*tseg1 > btc->tseg1_max) {
		*tseg1 = btc->tseg1_max;
		*tseg2 = tseg - *tseg1;
	}
	return 1000 * (tseg + 1 - *tseg2) / (tseg + 1);
}

static 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);
	long best_error = 1000000000, error = 0;
	int best_tseg = 0, best_brp = 0, brp = 0;
	int tsegall, tseg = 0, tseg1 = 0, tseg2 = 0;
	int spt_error = 1000, spt = 0, sampl_pt;
	long rate;
	u64 v64;

	/* Use CIA recommended sample points */
	if (bt->sample_point) {
		sampl_pt = bt->sample_point;
	} else {
		if (bt->bitrate > 800000)
			sampl_pt = 750;
		else if (bt->bitrate > 500000)
			sampl_pt = 800;
		else
			sampl_pt = 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 = 1 + tseg / 2;
		/* Compute all possible tseg choices (tseg=tseg1+tseg2) */
		brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2;
		/* chose 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;
		rate = priv->clock.freq / (brp * tsegall);
		error = bt->bitrate - rate;
		/* tseg brp biterror */
		if (error < 0)
			error = -error;
		if (error > best_error)
			continue;
		best_error = error;
		if (error == 0) {
			spt = can_update_spt(btc, sampl_pt, tseg / 2,
					     &tseg1, &tseg2);
			error = sampl_pt - spt;
			if (error < 0)
				error = -error;
			if (error > spt_error)
				continue;
			spt_error = error;
		}
		best_tseg = tseg / 2;
		best_brp = brp;
		if (error == 0)
			break;
	}

	if (best_error) {
		/* Error in one-tenth of a percent */
		error = (best_error * 1000) / bt->bitrate;
		if (error > CAN_CALC_MAX_ERROR) {
			netdev_err(dev,
				   "bitrate error %ld.%ld%% too high\n",
				   error / 10, error % 10);
			return -EDOM;
		} else {
			netdev_warn(dev, "bitrate error %ld.%ld%%\n",
				    error / 10, error % 10);
		}
	}

	/* real sample point */
	bt->sample_point = can_update_spt(btc, sampl_pt, best_tseg,
					  &tseg1, &tseg2);

	v64 = (u64)best_brp * 1000000000UL;
	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 bit-rate */
	bt->bitrate = priv->clock.freq / (bt->brp * (tseg1 + tseg2 + 1));

	return 0;
}

/*
 * 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);
	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;
}