calc_bittiming.c

  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 * Copyright (C) 2021-2025 Vincent Mailhol <mailhol@kernel.org>
  6 */
  7
  8#include <linux/units.h>
  9#include <linux/can/dev.h>
 10
 11#define CAN_CALC_MAX_ERROR 500 /* max error 5% */
 12
 13/* CiA recommended sample points for Non Return to Zero encoding. */
 14static int can_calc_sample_point_nrz(const struct can_bittiming *bt)
 15{
 16	if (bt->bitrate > 800 * KILO /* BPS */)
 17		return 750;
 18
 19	if (bt->bitrate > 500 * KILO /* BPS */)
 20		return 800;
 21
 22	return 875;
 23}
 24
 25/* Sample points for Pulse-Width Modulation encoding. */
 26static int can_calc_sample_point_pwm(const struct can_bittiming *bt)
 27{
 28	if (bt->bitrate > 15 * MEGA /* BPS */)
 29		return 625;
 30
 31	if (bt->bitrate > 9 * MEGA /* BPS */)
 32		return 600;
 33
 34	if (bt->bitrate > 4 * MEGA /* BPS */)
 35		return 560;
 36
 37	return 520;
 38}
 39
 40/* Bit-timing calculation derived from:
 41 *
 42 * Code based on LinCAN sources and H8S2638 project
 43 * Copyright 2004-2006 Pavel Pisa - DCE FELK CVUT cz
 44 * Copyright 2005      Stanislav Marek
 45 * email: pisa@cmp.felk.cvut.cz
 46 *
 47 * Calculates proper bit-timing parameters for a specified bit-rate
 48 * and sample-point, which can then be used to set the bit-timing
 49 * registers of the CAN controller. You can find more information
 50 * in the header file linux/can/netlink.h.
 51 */
 52static int
 53can_update_sample_point(const struct can_bittiming_const *btc,
 54			const unsigned int sample_point_reference, const unsigned int tseg,
 55			unsigned int *tseg1_ptr, unsigned int *tseg2_ptr,
 56			unsigned int *sample_point_error_ptr)
 57{
 58	unsigned int sample_point_error, best_sample_point_error = UINT_MAX;
 59	unsigned int sample_point, best_sample_point = 0;
 60	unsigned int tseg1, tseg2;
 61	int i;
 62
 63	for (i = 0; i <= 1; i++) {
 64		tseg2 = tseg + CAN_SYNC_SEG -
 65			(sample_point_reference * (tseg + CAN_SYNC_SEG)) /
 66			1000 - i;
 67		tseg2 = clamp(tseg2, btc->tseg2_min, btc->tseg2_max);
 68		tseg1 = tseg - tseg2;
 69		if (tseg1 > btc->tseg1_max) {
 70			tseg1 = btc->tseg1_max;
 71			tseg2 = tseg - tseg1;
 72		}
 73
 74		sample_point = 1000 * (tseg + CAN_SYNC_SEG - tseg2) /
 75			(tseg + CAN_SYNC_SEG);
 76		sample_point_error = abs(sample_point_reference - sample_point);
 77
 78		if (sample_point <= sample_point_reference &&
 79		    sample_point_error < best_sample_point_error) {
 80			best_sample_point = sample_point;
 81			best_sample_point_error = sample_point_error;
 82			*tseg1_ptr = tseg1;
 83			*tseg2_ptr = tseg2;
 84		}
 85	}
 86
 87	if (sample_point_error_ptr)
 88		*sample_point_error_ptr = best_sample_point_error;
 89
 90	return best_sample_point;
 91}
 92
 93int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 94		       const struct can_bittiming_const *btc, struct netlink_ext_ack *extack)
 95{
 96	struct can_priv *priv = netdev_priv(dev);
 97	unsigned int bitrate;			/* current bitrate */
 98	unsigned int bitrate_error;		/* diff between calculated and reference value */
 99	unsigned int best_bitrate_error = UINT_MAX;
100	unsigned int sample_point_error;	/* diff between calculated and reference value */
101	unsigned int best_sample_point_error = UINT_MAX;
102	unsigned int sample_point_reference;	/* reference sample point */
103	unsigned int best_tseg = 0;		/* current best value for tseg */
104	unsigned int best_brp = 0;		/* current best value for brp */
105	unsigned int brp, tsegall, tseg, tseg1 = 0, tseg2 = 0;
106	u64 v64;
107	int err;
108
109	if (bt->sample_point)
110		sample_point_reference = bt->sample_point;
111	else if (btc == priv->xl.data_bittiming_const &&
112		 (priv->ctrlmode & CAN_CTRLMODE_XL_TMS))
113		sample_point_reference = can_calc_sample_point_pwm(bt);
114	else
115		sample_point_reference = can_calc_sample_point_nrz(bt);
116
117	/* tseg even = round down, odd = round up */
118	for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1;
119	     tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) {
120		tsegall = CAN_SYNC_SEG + tseg / 2;
121
122		/* Compute all possible tseg choices (tseg=tseg1+tseg2) */
123		brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2;
124
125		/* choose brp step which is possible in system */
126		brp = (brp / btc->brp_inc) * btc->brp_inc;
127		if (brp < btc->brp_min || brp > btc->brp_max)
128			continue;
129
130		bitrate = priv->clock.freq / (brp * tsegall);
131		bitrate_error = abs(bt->bitrate - bitrate);
132
133		/* tseg brp biterror */
134		if (bitrate_error > best_bitrate_error)
135			continue;
136
137		/* reset sample point error if we have a better bitrate */
138		if (bitrate_error < best_bitrate_error)
139			best_sample_point_error = UINT_MAX;
140
141		can_update_sample_point(btc, sample_point_reference, tseg / 2,
142					&tseg1, &tseg2, &sample_point_error);
143		if (sample_point_error >= best_sample_point_error)
144			continue;
145
146		best_sample_point_error = sample_point_error;
147		best_bitrate_error = bitrate_error;
148		best_tseg = tseg / 2;
149		best_brp = brp;
150
151		if (bitrate_error == 0 && sample_point_error == 0)
152			break;
153	}
154
155	if (best_bitrate_error) {
156		/* Error in one-hundredth of a percent */
157		v64 = (u64)best_bitrate_error * 10000;
158		do_div(v64, bt->bitrate);
159		bitrate_error = (u32)v64;
160		/* print at least 0.01% if the error is smaller */
161		bitrate_error = max(bitrate_error, 1U);
162		if (bitrate_error > CAN_CALC_MAX_ERROR) {
163			NL_SET_ERR_MSG_FMT(extack,
164					   "bitrate error: %u.%02u%% too high",
165					   bitrate_error / 100,
166					   bitrate_error % 100);
167			return -EINVAL;
168		}
169		NL_SET_ERR_MSG_FMT(extack,
170				   "bitrate error: %u.%02u%%",
171				   bitrate_error / 100, bitrate_error % 100);
172	}
173
174	/* real sample point */
175	bt->sample_point = can_update_sample_point(btc, sample_point_reference,
176						   best_tseg, &tseg1, &tseg2,
177						   NULL);
178
179	v64 = (u64)best_brp * 1000 * 1000 * 1000;
180	do_div(v64, priv->clock.freq);
181	bt->tq = (u32)v64;
182	bt->prop_seg = tseg1 / 2;
183	bt->phase_seg1 = tseg1 - bt->prop_seg;
184	bt->phase_seg2 = tseg2;
185
186	can_sjw_set_default(bt);
187
188	err = can_sjw_check(dev, bt, btc, extack);
189	if (err)
190		return err;
191
192	bt->brp = best_brp;
193
194	/* real bitrate */
195	bt->bitrate = priv->clock.freq /
196		(bt->brp * can_bit_time(bt));
197
198	return 0;
199}
200
201void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
202		   const struct can_bittiming *dbt,
203		   u32 tdc_mask, u32 *ctrlmode, u32 ctrlmode_supported)
204
205{
206	u32 tdc_auto = tdc_mask & CAN_CTRLMODE_TDC_AUTO_MASK;
207
208	if (!tdc_const || !(ctrlmode_supported & tdc_auto))
209		return;
210
211	*ctrlmode &= ~tdc_mask;
212
213	/* As specified in ISO 11898-1 section 11.3.3 "Transmitter
214	 * delay compensation" (TDC) is only applicable if data BRP is
215	 * one or two.
216	 */
217	if (dbt->brp == 1 || dbt->brp == 2) {
218		/* Sample point in clock periods */
219		u32 sample_point_in_tc = (CAN_SYNC_SEG + dbt->prop_seg +
220					  dbt->phase_seg1) * dbt->brp;
221
222		if (sample_point_in_tc < tdc_const->tdco_min)
223			return;
224		tdc->tdco = min(sample_point_in_tc, tdc_const->tdco_max);
225		*ctrlmode |= tdc_auto;
226	}
227}
228
229int can_calc_pwm(struct net_device *dev, struct netlink_ext_ack *extack)
230{
231	struct can_priv *priv = netdev_priv(dev);
232	const struct can_pwm_const *pwm_const = priv->xl.pwm_const;
233	struct can_pwm *pwm = &priv->xl.pwm;
234	u32 xl_tqmin = can_bit_time_tqmin(&priv->xl.data_bittiming);
235	u32 xl_ns = can_tqmin_to_ns(xl_tqmin, priv->clock.freq);
236	u32 nom_tqmin = can_bit_time_tqmin(&priv->bittiming);
237	int pwm_per_bit_max = xl_tqmin / (pwm_const->pwms_min + pwm_const->pwml_min);
238	int pwm_per_bit;
239	u32 pwm_tqmin;
240
241	/* For 5 MB/s databitrate or greater, xl_ns < CAN_PWM_NS_MAX
242	 * giving us a pwm_per_bit of 1 and the loop immediately breaks
243	 */
244	for (pwm_per_bit = DIV_ROUND_UP(xl_ns, CAN_PWM_NS_MAX);
245	     pwm_per_bit <= pwm_per_bit_max; pwm_per_bit++)
246		if (xl_tqmin % pwm_per_bit == 0)
247			break;
248
249	if (pwm_per_bit > pwm_per_bit_max) {
250		NL_SET_ERR_MSG_FMT(extack,
251				   "Can not divide the XL data phase's bit time: %u tqmin into multiple PWM symbols",
252				   xl_tqmin);
253		return -EINVAL;
254	}
255
256	pwm_tqmin = xl_tqmin / pwm_per_bit;
257	pwm->pwms = DIV_ROUND_UP_POW2(pwm_tqmin, 4);
258	pwm->pwml = pwm_tqmin - pwm->pwms;
259	pwm->pwmo = nom_tqmin % pwm_tqmin;
260
261	return 0;
262}