xref: /openbmc/linux/include/linux/can/bittiming.h (revision 65db3d8b)
1 /* SPDX-License-Identifier: GPL-2.0-only */
2 /* Copyright (c) 2020 Pengutronix, Marc Kleine-Budde <kernel@pengutronix.de>
3  * Copyright (c) 2021 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
4  */
5 
6 #ifndef _CAN_BITTIMING_H
7 #define _CAN_BITTIMING_H
8 
9 #include <linux/netdevice.h>
10 #include <linux/can/netlink.h>
11 
12 #define CAN_SYNC_SEG 1
13 
14 #define CAN_BITRATE_UNSET 0
15 #define CAN_BITRATE_UNKNOWN (-1U)
16 
17 #define CAN_CTRLMODE_TDC_MASK					\
18 	(CAN_CTRLMODE_TDC_AUTO | CAN_CTRLMODE_TDC_MANUAL)
19 
20 /*
21  * struct can_tdc - CAN FD Transmission Delay Compensation parameters
22  *
23  * At high bit rates, the propagation delay from the TX pin to the RX
24  * pin of the transceiver causes measurement errors: the sample point
25  * on the RX pin might occur on the previous bit.
26  *
27  * To solve this issue, ISO 11898-1 introduces in section 11.3.3
28  * "Transmitter delay compensation" a SSP (Secondary Sample Point)
29  * equal to the distance from the start of the bit time on the TX pin
30  * to the actual measurement on the RX pin.
31  *
32  * This structure contains the parameters to calculate that SSP.
33  *
34  * -+----------- one bit ----------+-- TX pin
35  *  |<--- Sample Point --->|
36  *
37  *                         --+----------- one bit ----------+-- RX pin
38  *  |<-------- TDCV -------->|
39  *                           |<------- TDCO ------->|
40  *  |<----------- Secondary Sample Point ---------->|
41  *
42  * To increase precision, contrary to the other bittiming parameters
43  * which are measured in time quanta, the TDC parameters are measured
44  * in clock periods (also referred as "minimum time quantum" in ISO
45  * 11898-1).
46  *
47  * @tdcv: Transmitter Delay Compensation Value. The time needed for
48  *	the signal to propagate, i.e. the distance, in clock periods,
49  *	from the start of the bit on the TX pin to when it is received
50  *	on the RX pin. @tdcv depends on the controller modes:
51  *
52  *	  CAN_CTRLMODE_TDC_AUTO is set: The transceiver dynamically
53  *	  measures @tdcv for each transmitted CAN FD frame and the
54  *	  value provided here should be ignored.
55  *
56  *	  CAN_CTRLMODE_TDC_MANUAL is set: use the fixed provided @tdcv
57  *	  value.
58  *
59  *	N.B. CAN_CTRLMODE_TDC_AUTO and CAN_CTRLMODE_TDC_MANUAL are
60  *	mutually exclusive. Only one can be set at a time. If both
61  *	CAN_TDC_CTRLMODE_AUTO and CAN_TDC_CTRLMODE_MANUAL are unset,
62  *	TDC is disabled and all the values of this structure should be
63  *	ignored.
64  *
65  * @tdco: Transmitter Delay Compensation Offset. Offset value, in
66  *	clock periods, defining the distance between the start of the
67  *	bit reception on the RX pin of the transceiver and the SSP
68  *	position such that SSP = @tdcv + @tdco.
69  *
70  * @tdcf: Transmitter Delay Compensation Filter window. Defines the
71  *	minimum value for the SSP position in clock periods. If the
72  *	SSP position is less than @tdcf, then no delay compensations
73  *	occur and the normal sampling point is used instead. The
74  *	feature is enabled if and only if @tdcv is set to zero
75  *	(automatic mode) and @tdcf is configured to a value greater
76  *	than @tdco.
77  */
78 struct can_tdc {
79 	u32 tdcv;
80 	u32 tdco;
81 	u32 tdcf;
82 };
83 
84 /*
85  * struct can_tdc_const - CAN hardware-dependent constant for
86  *	Transmission Delay Compensation
87  *
88  * @tdcv_min: Transmitter Delay Compensation Value minimum value. If
89  *	the controller does not support manual mode for tdcv
90  *	(c.f. flag CAN_CTRLMODE_TDC_MANUAL) then this value is
91  *	ignored.
92  * @tdcv_max: Transmitter Delay Compensation Value maximum value. If
93  *	the controller does not support manual mode for tdcv
94  *	(c.f. flag CAN_CTRLMODE_TDC_MANUAL) then this value is
95  *	ignored.
96  *
97  * @tdco_min: Transmitter Delay Compensation Offset minimum value.
98  * @tdco_max: Transmitter Delay Compensation Offset maximum value.
99  *	Should not be zero. If the controller does not support TDC,
100  *	then the pointer to this structure should be NULL.
101  *
102  * @tdcf_min: Transmitter Delay Compensation Filter window minimum
103  *	value. If @tdcf_max is zero, this value is ignored.
104  * @tdcf_max: Transmitter Delay Compensation Filter window maximum
105  *	value. Should be set to zero if the controller does not
106  *	support this feature.
107  */
108 struct can_tdc_const {
109 	u32 tdcv_min;
110 	u32 tdcv_max;
111 	u32 tdco_min;
112 	u32 tdco_max;
113 	u32 tdcf_min;
114 	u32 tdcf_max;
115 };
116 
117 #ifdef CONFIG_CAN_CALC_BITTIMING
118 int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
119 		       const struct can_bittiming_const *btc, struct netlink_ext_ack *extack);
120 
121 void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
122 		   const struct can_bittiming *dbt,
123 		   u32 *ctrlmode, u32 ctrlmode_supported);
124 #else /* !CONFIG_CAN_CALC_BITTIMING */
125 static inline int
can_calc_bittiming(const struct net_device * dev,struct can_bittiming * bt,const struct can_bittiming_const * btc,struct netlink_ext_ack * extack)126 can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
127 		   const struct can_bittiming_const *btc, struct netlink_ext_ack *extack)
128 {
129 	netdev_err(dev, "bit-timing calculation not available\n");
130 	return -EINVAL;
131 }
132 
133 static inline 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)134 can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
135 	      const struct can_bittiming *dbt,
136 	      u32 *ctrlmode, u32 ctrlmode_supported)
137 {
138 }
139 #endif /* CONFIG_CAN_CALC_BITTIMING */
140 
141 void can_sjw_set_default(struct can_bittiming *bt);
142 
143 int can_sjw_check(const struct net_device *dev, const struct can_bittiming *bt,
144 		  const struct can_bittiming_const *btc, struct netlink_ext_ack *extack);
145 
146 int can_get_bittiming(const struct net_device *dev, struct can_bittiming *bt,
147 		      const struct can_bittiming_const *btc,
148 		      const u32 *bitrate_const,
149 		      const unsigned int bitrate_const_cnt,
150 		      struct netlink_ext_ack *extack);
151 
152 /*
153  * can_bit_time() - Duration of one bit
154  *
155  * Please refer to ISO 11898-1:2015, section 11.3.1.1 "Bit time" for
156  * additional information.
157  *
158  * Return: the number of time quanta in one bit.
159  */
can_bit_time(const struct can_bittiming * bt)160 static inline unsigned int can_bit_time(const struct can_bittiming *bt)
161 {
162 	return CAN_SYNC_SEG + bt->prop_seg + bt->phase_seg1 + bt->phase_seg2;
163 }
164 
165 #endif /* !_CAN_BITTIMING_H */
166