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  */
24 static int
25 can_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 
65 int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
66 		       const struct can_bittiming_const *btc)
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 
80 	/* Use CiA recommended sample points */
81 	if (bt->sample_point) {
82 		sample_point_nominal = bt->sample_point;
83 	} else {
84 		if (bt->bitrate > 800 * KILO /* BPS */)
85 			sample_point_nominal = 750;
86 		else if (bt->bitrate > 500 * KILO /* BPS */)
87 			sample_point_nominal = 800;
88 		else
89 			sample_point_nominal = 875;
90 	}
91 
92 	/* tseg even = round down, odd = round up */
93 	for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1;
94 	     tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) {
95 		tsegall = CAN_SYNC_SEG + tseg / 2;
96 
97 		/* Compute all possible tseg choices (tseg=tseg1+tseg2) */
98 		brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2;
99 
100 		/* choose brp step which is possible in system */
101 		brp = (brp / btc->brp_inc) * btc->brp_inc;
102 		if (brp < btc->brp_min || brp > btc->brp_max)
103 			continue;
104 
105 		bitrate = priv->clock.freq / (brp * tsegall);
106 		bitrate_error = abs(bt->bitrate - bitrate);
107 
108 		/* tseg brp biterror */
109 		if (bitrate_error > best_bitrate_error)
110 			continue;
111 
112 		/* reset sample point error if we have a better bitrate */
113 		if (bitrate_error < best_bitrate_error)
114 			best_sample_point_error = UINT_MAX;
115 
116 		can_update_sample_point(btc, sample_point_nominal, tseg / 2,
117 					&tseg1, &tseg2, &sample_point_error);
118 		if (sample_point_error >= best_sample_point_error)
119 			continue;
120 
121 		best_sample_point_error = sample_point_error;
122 		best_bitrate_error = bitrate_error;
123 		best_tseg = tseg / 2;
124 		best_brp = brp;
125 
126 		if (bitrate_error == 0 && sample_point_error == 0)
127 			break;
128 	}
129 
130 	if (best_bitrate_error) {
131 		/* Error in one-tenth of a percent */
132 		v64 = (u64)best_bitrate_error * 1000;
133 		do_div(v64, bt->bitrate);
134 		bitrate_error = (u32)v64;
135 		if (bitrate_error > CAN_CALC_MAX_ERROR) {
136 			netdev_err(dev,
137 				   "bitrate error %d.%d%% too high\n",
138 				   bitrate_error / 10, bitrate_error % 10);
139 			return -EDOM;
140 		}
141 		netdev_warn(dev, "bitrate error %d.%d%%\n",
142 			    bitrate_error / 10, bitrate_error % 10);
143 	}
144 
145 	/* real sample point */
146 	bt->sample_point = can_update_sample_point(btc, sample_point_nominal,
147 						   best_tseg, &tseg1, &tseg2,
148 						   NULL);
149 
150 	v64 = (u64)best_brp * 1000 * 1000 * 1000;
151 	do_div(v64, priv->clock.freq);
152 	bt->tq = (u32)v64;
153 	bt->prop_seg = tseg1 / 2;
154 	bt->phase_seg1 = tseg1 - bt->prop_seg;
155 	bt->phase_seg2 = tseg2;
156 
157 	/* check for sjw user settings */
158 	if (!bt->sjw || !btc->sjw_max) {
159 		bt->sjw = 1;
160 	} else {
161 		/* bt->sjw is at least 1 -> sanitize upper bound to sjw_max */
162 		if (bt->sjw > btc->sjw_max)
163 			bt->sjw = btc->sjw_max;
164 		/* bt->sjw must not be higher than tseg2 */
165 		if (tseg2 < bt->sjw)
166 			bt->sjw = tseg2;
167 	}
168 
169 	bt->brp = best_brp;
170 
171 	/* real bitrate */
172 	bt->bitrate = priv->clock.freq /
173 		(bt->brp * (CAN_SYNC_SEG + tseg1 + tseg2));
174 
175 	return 0;
176 }
177 
178 void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
179 		   const struct can_bittiming *dbt,
180 		   u32 *ctrlmode, u32 ctrlmode_supported)
181 
182 {
183 	if (!tdc_const || !(ctrlmode_supported & CAN_CTRLMODE_TDC_AUTO))
184 		return;
185 
186 	*ctrlmode &= ~CAN_CTRLMODE_TDC_MASK;
187 
188 	/* As specified in ISO 11898-1 section 11.3.3 "Transmitter
189 	 * delay compensation" (TDC) is only applicable if data BRP is
190 	 * one or two.
191 	 */
192 	if (dbt->brp == 1 || dbt->brp == 2) {
193 		/* Sample point in clock periods */
194 		u32 sample_point_in_tc = (CAN_SYNC_SEG + dbt->prop_seg +
195 					  dbt->phase_seg1) * dbt->brp;
196 
197 		if (sample_point_in_tc < tdc_const->tdco_min)
198 			return;
199 		tdc->tdco = min(sample_point_in_tc, tdc_const->tdco_max);
200 		*ctrlmode |= CAN_CTRLMODE_TDC_AUTO;
201 	}
202 }
203