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 */
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 project
15 * Copyright 2004-2006 Pavel Pisa - DCE FELK CVUT cz
16 * Copyright 2005      Stanislav Marek
17 * email: pisa@cmp.felk.cvut.cz
18 *
19 * Calculates proper bit-timing parameters for a specified bit-rate
20 * and sample-point, which can then be used to set the bit-timing
21 * registers of the CAN controller. You can find more information
22 * in the header file linux/can/netlink.h.
23 */
24static int
25can_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		else
90			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 "Transmitter
185	 * delay compensation" (TDC) is only applicable if data BRP is
186	 * 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