xref: /linux/include/linux/can/length.h (revision cdd5b5a9761fd66d17586e4f4ba6588c70e640ea)
1 /* SPDX-License-Identifier: GPL-2.0 */
2 /* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
3  * Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
4  * Copyright (C) 2020, 2023 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
5  */
6 
7 #ifndef _CAN_LENGTH_H
8 #define _CAN_LENGTH_H
9 
10 #include <linux/bits.h>
11 #include <linux/can.h>
12 #include <linux/can/netlink.h>
13 #include <linux/math.h>
14 
15 /*
16  * Size of a Classical CAN Standard Frame header in bits
17  *
18  * Name of Field				Bits
19  * ---------------------------------------------------------
20  * Start Of Frame (SOF)				1
21  * Arbitration field:
22  *	base ID					11
23  *	Remote Transmission Request (RTR)	1
24  * Control field:
25  *	IDentifier Extension bit (IDE)		1
26  *	FD Format indicator (FDF)		1
27  *	Data Length Code (DLC)			4
28  *
29  * including all fields preceding the data field, ignoring bitstuffing
30  */
31 #define CAN_FRAME_HEADER_SFF_BITS 19
32 
33 /*
34  * Size of a Classical CAN Extended Frame header in bits
35  *
36  * Name of Field				Bits
37  * ---------------------------------------------------------
38  * Start Of Frame (SOF)				1
39  * Arbitration field:
40  *	base ID					11
41  *	Substitute Remote Request (SRR)		1
42  *	IDentifier Extension bit (IDE)		1
43  *	ID extension				18
44  *	Remote Transmission Request (RTR)	1
45  * Control field:
46  *	FD Format indicator (FDF)		1
47  *	Reserved bit (r0)			1
48  *	Data length code (DLC)			4
49  *
50  * including all fields preceding the data field, ignoring bitstuffing
51  */
52 #define CAN_FRAME_HEADER_EFF_BITS 39
53 
54 /*
55  * Size of a CAN-FD Standard Frame in bits
56  *
57  * Name of Field				Bits
58  * ---------------------------------------------------------
59  * Start Of Frame (SOF)				1
60  * Arbitration field:
61  *	base ID					11
62  *	Remote Request Substitution (RRS)	1
63  * Control field:
64  *	IDentifier Extension bit (IDE)		1
65  *	FD Format indicator (FDF)		1
66  *	Reserved bit (res)			1
67  *	Bit Rate Switch (BRS)			1
68  *	Error Status Indicator (ESI)		1
69  *	Data length code (DLC)			4
70  *
71  * including all fields preceding the data field, ignoring bitstuffing
72  */
73 #define CANFD_FRAME_HEADER_SFF_BITS 22
74 
75 /*
76  * Size of a CAN-FD Extended Frame in bits
77  *
78  * Name of Field				Bits
79  * ---------------------------------------------------------
80  * Start Of Frame (SOF)				1
81  * Arbitration field:
82  *	base ID					11
83  *	Substitute Remote Request (SRR)		1
84  *	IDentifier Extension bit (IDE)		1
85  *	ID extension				18
86  *	Remote Request Substitution (RRS)	1
87  * Control field:
88  *	FD Format indicator (FDF)		1
89  *	Reserved bit (res)			1
90  *	Bit Rate Switch (BRS)			1
91  *	Error Status Indicator (ESI)		1
92  *	Data length code (DLC)			4
93  *
94  * including all fields preceding the data field, ignoring bitstuffing
95  */
96 #define CANFD_FRAME_HEADER_EFF_BITS 41
97 
98 /*
99  * Size of a CAN CRC Field in bits
100  *
101  * Name of Field			Bits
102  * ---------------------------------------------------------
103  * CRC sequence (CRC15)			15
104  * CRC Delimiter			1
105  *
106  * ignoring bitstuffing
107  */
108 #define CAN_FRAME_CRC_FIELD_BITS 16
109 
110 /*
111  * Size of a CAN-FD CRC17 Field in bits (length: 0..16)
112  *
113  * Name of Field			Bits
114  * ---------------------------------------------------------
115  * Stuff Count				4
116  * CRC Sequence (CRC17)			17
117  * CRC Delimiter			1
118  * Fixed stuff bits			6
119  */
120 #define CANFD_FRAME_CRC17_FIELD_BITS 28
121 
122 /*
123  * Size of a CAN-FD CRC21 Field in bits (length: 20..64)
124  *
125  * Name of Field			Bits
126  * ---------------------------------------------------------
127  * Stuff Count				4
128  * CRC sequence (CRC21)			21
129  * CRC Delimiter			1
130  * Fixed stuff bits			7
131  */
132 #define CANFD_FRAME_CRC21_FIELD_BITS 33
133 
134 /*
135  * Size of a CAN(-FD) Frame footer in bits
136  *
137  * Name of Field			Bits
138  * ---------------------------------------------------------
139  * ACK slot				1
140  * ACK delimiter			1
141  * End Of Frame (EOF)			7
142  *
143  * including all fields following the CRC field
144  */
145 #define CAN_FRAME_FOOTER_BITS 9
146 
147 /*
148  * First part of the Inter Frame Space
149  * (a.k.a. IMF - intermission field)
150  */
151 #define CAN_INTERMISSION_BITS 3
152 
153 /**
154  * can_bitstuffing_len() - Calculate the maximum length with bitstuffing
155  * @destuffed_len: length of a destuffed bit stream
156  *
157  * The worst bit stuffing case is a sequence in which dominant and
158  * recessive bits alternate every four bits:
159  *
160  *   Destuffed: 1 1111  0000  1111  0000  1111
161  *   Stuffed:   1 1111o 0000i 1111o 0000i 1111o
162  *
163  * Nomenclature
164  *
165  *  - "0": dominant bit
166  *  - "o": dominant stuff bit
167  *  - "1": recessive bit
168  *  - "i": recessive stuff bit
169  *
170  * Aside from the first bit, one stuff bit is added every four bits.
171  *
172  * Return: length of the stuffed bit stream in the worst case scenario.
173  */
174 #define can_bitstuffing_len(destuffed_len)			\
175 	(destuffed_len + (destuffed_len - 1) / 4)
176 
177 #define __can_bitstuffing_len(bitstuffing, destuffed_len)	\
178 	(bitstuffing ? can_bitstuffing_len(destuffed_len) :	\
179 		       destuffed_len)
180 
181 #define __can_cc_frame_bits(is_eff, bitstuffing,		\
182 			    intermission, data_len)		\
183 (								\
184 	__can_bitstuffing_len(bitstuffing,			\
185 		(is_eff ? CAN_FRAME_HEADER_EFF_BITS :		\
186 			  CAN_FRAME_HEADER_SFF_BITS) +		\
187 		(data_len) * BITS_PER_BYTE +			\
188 		CAN_FRAME_CRC_FIELD_BITS) +			\
189 	CAN_FRAME_FOOTER_BITS +					\
190 	(intermission ? CAN_INTERMISSION_BITS : 0)		\
191 )
192 
193 #define __can_fd_frame_bits(is_eff, bitstuffing,		\
194 			    intermission, data_len)		\
195 (								\
196 	__can_bitstuffing_len(bitstuffing,			\
197 		(is_eff ? CANFD_FRAME_HEADER_EFF_BITS :		\
198 			  CANFD_FRAME_HEADER_SFF_BITS) +	\
199 		(data_len) * BITS_PER_BYTE) +			\
200 	((data_len) <= 16 ?					\
201 		CANFD_FRAME_CRC17_FIELD_BITS :			\
202 		CANFD_FRAME_CRC21_FIELD_BITS) +			\
203 	CAN_FRAME_FOOTER_BITS +					\
204 	(intermission ? CAN_INTERMISSION_BITS : 0)		\
205 )
206 
207 /**
208  * can_frame_bits() - Calculate the number of bits on the wire in a
209  *	CAN frame
210  * @is_fd: true: CAN-FD frame; false: Classical CAN frame.
211  * @is_eff: true: Extended frame; false: Standard frame.
212  * @bitstuffing: true: calculate the bitstuffing worst case; false:
213  *	calculate the bitstuffing best case (no dynamic
214  *	bitstuffing). CAN-FD's fixed stuff bits are always included.
215  * @intermission: if and only if true, include the inter frame space
216  *	assuming no bus idle (i.e. only the intermission). Strictly
217  *	speaking, the inter frame space is not part of the
218  *	frame. However, it is needed when calculating the delay
219  *	between the Start Of Frame of two consecutive frames.
220  * @data_len: length of the data field in bytes. Correspond to
221  *	can(fd)_frame->len. Should be zero for remote frames. No
222  *	sanitization is done on @data_len and it shall have no side
223  *	effects.
224  *
225  * Return: the numbers of bits on the wire of a CAN frame.
226  */
227 #define can_frame_bits(is_fd, is_eff, bitstuffing,		\
228 		       intermission, data_len)			\
229 (								\
230 	is_fd ? __can_fd_frame_bits(is_eff, bitstuffing,	\
231 				    intermission, data_len) :	\
232 		__can_cc_frame_bits(is_eff, bitstuffing,	\
233 				    intermission, data_len)	\
234 )
235 
236 /*
237  * Number of bytes in a CAN frame
238  * (rounded up, including intermission)
239  */
240 #define can_frame_bytes(is_fd, is_eff, bitstuffing, data_len)	\
241 	DIV_ROUND_UP(can_frame_bits(is_fd, is_eff, bitstuffing,	\
242 				    true, data_len),		\
243 		     BITS_PER_BYTE)
244 
245 /*
246  * Maximum size of a Classical CAN frame
247  * (rounded up, ignoring bitstuffing but including intermission)
248  */
249 #define CAN_FRAME_LEN_MAX can_frame_bytes(false, true, false, CAN_MAX_DLEN)
250 
251 /*
252  * Maximum size of a CAN-FD frame
253  * (rounded up, ignoring dynamic bitstuffing but including intermission)
254  */
255 #define CANFD_FRAME_LEN_MAX can_frame_bytes(true, true, false, CANFD_MAX_DLEN)
256 
257 /*
258  * can_cc_dlc2len(value) - convert a given data length code (dlc) of a
259  * Classical CAN frame into a valid data length of max. 8 bytes.
260  *
261  * To be used in the CAN netdriver receive path to ensure conformance with
262  * ISO 11898-1 Chapter 8.4.2.3 (DLC field)
263  */
264 #define can_cc_dlc2len(dlc)	(min_t(u8, (dlc), CAN_MAX_DLEN))
265 
266 /* helper to get the data length code (DLC) for Classical CAN raw DLC access */
can_get_cc_dlc(const struct can_frame * cf,const u32 ctrlmode)267 static inline u8 can_get_cc_dlc(const struct can_frame *cf, const u32 ctrlmode)
268 {
269 	/* return len8_dlc as dlc value only if all conditions apply */
270 	if ((ctrlmode & CAN_CTRLMODE_CC_LEN8_DLC) &&
271 	    (cf->len == CAN_MAX_DLEN) &&
272 	    (cf->len8_dlc > CAN_MAX_DLEN && cf->len8_dlc <= CAN_MAX_RAW_DLC))
273 		return cf->len8_dlc;
274 
275 	/* return the payload length as dlc value */
276 	return cf->len;
277 }
278 
279 /* helper to set len and len8_dlc value for Classical CAN raw DLC access */
can_frame_set_cc_len(struct can_frame * cf,const u8 dlc,const u32 ctrlmode)280 static inline void can_frame_set_cc_len(struct can_frame *cf, const u8 dlc,
281 					const u32 ctrlmode)
282 {
283 	/* the caller already ensured that dlc is a value from 0 .. 15 */
284 	if (ctrlmode & CAN_CTRLMODE_CC_LEN8_DLC && dlc > CAN_MAX_DLEN)
285 		cf->len8_dlc = dlc;
286 
287 	/* limit the payload length 'len' to CAN_MAX_DLEN */
288 	cf->len = can_cc_dlc2len(dlc);
289 }
290 
291 /* get data length from raw data length code (DLC) */
292 u8 can_fd_dlc2len(u8 dlc);
293 
294 /* map the sanitized data length to an appropriate data length code */
295 u8 can_fd_len2dlc(u8 len);
296 
297 /* calculate the CAN Frame length in bytes of a given skb */
298 unsigned int can_skb_get_frame_len(const struct sk_buff *skb);
299 
300 /* map the data length to an appropriate data link layer length */
canfd_sanitize_len(u8 len)301 static inline u8 canfd_sanitize_len(u8 len)
302 {
303 	return can_fd_dlc2len(can_fd_len2dlc(len));
304 }
305 
306 #endif /* !_CAN_LENGTH_H */
307