1 // SPDX-License-Identifier: GPL-2.0-only
2 /* Copyright (C) 2012, 2020 Oliver Hartkopp <socketcan@hartkopp.net>
3  */
4 
5 #include <linux/can/dev.h>
6 
7 /* CAN DLC to real data length conversion helpers */
8 
9 static const u8 dlc2len[] = {
10 	0, 1, 2, 3, 4, 5, 6, 7,
11 	8, 12, 16, 20, 24, 32, 48, 64
12 };
13 
14 /* get data length from raw data length code (DLC) */
can_fd_dlc2len(u8 dlc)15 u8 can_fd_dlc2len(u8 dlc)
16 {
17 	return dlc2len[dlc & 0x0F];
18 }
19 EXPORT_SYMBOL_GPL(can_fd_dlc2len);
20 
21 static const u8 len2dlc[] = {
22 	0, 1, 2, 3, 4, 5, 6, 7, 8,	/* 0 - 8 */
23 	9, 9, 9, 9,			/* 9 - 12 */
24 	10, 10, 10, 10,			/* 13 - 16 */
25 	11, 11, 11, 11,			/* 17 - 20 */
26 	12, 12, 12, 12,			/* 21 - 24 */
27 	13, 13, 13, 13, 13, 13, 13, 13,	/* 25 - 32 */
28 	14, 14, 14, 14, 14, 14, 14, 14,	/* 33 - 40 */
29 	14, 14, 14, 14, 14, 14, 14, 14,	/* 41 - 48 */
30 	15, 15, 15, 15, 15, 15, 15, 15,	/* 49 - 56 */
31 	15, 15, 15, 15, 15, 15, 15, 15	/* 57 - 64 */
32 };
33 
34 /* map the sanitized data length to an appropriate data length code */
can_fd_len2dlc(u8 len)35 u8 can_fd_len2dlc(u8 len)
36 {
37 	/* check for length mapping table size at build time */
38 	BUILD_BUG_ON(ARRAY_SIZE(len2dlc) != CANFD_MAX_DLEN + 1);
39 
40 	if (unlikely(len > CANFD_MAX_DLEN))
41 		return CANFD_MAX_DLC;
42 
43 	return len2dlc[len];
44 }
45 EXPORT_SYMBOL_GPL(can_fd_len2dlc);
46 
47 /**
48  * can_skb_get_frame_len() - Calculate the CAN Frame length in bytes
49  * 	of a given skb.
50  * @skb: socket buffer of a CAN message.
51  *
52  * Do a rough calculation: bit stuffing is ignored and length in bits
53  * is rounded up to a length in bytes.
54  *
55  * Rationale: this function is to be used for the BQL functions
56  * (netdev_sent_queue() and netdev_completed_queue()) which expect a
57  * value in bytes. Just using skb->len is insufficient because it will
58  * return the constant value of CAN(FD)_MTU. Doing the bit stuffing
59  * calculation would be too expensive in term of computing resources
60  * for no noticeable gain.
61  *
62  * Remarks: The payload of CAN FD frames with BRS flag are sent at a
63  * different bitrate. Currently, the can-utils canbusload tool does
64  * not support CAN-FD yet and so we could not run any benchmark to
65  * measure the impact. There might be possible improvement here.
66  *
67  * Return: length in bytes.
68  */
can_skb_get_frame_len(const struct sk_buff * skb)69 unsigned int can_skb_get_frame_len(const struct sk_buff *skb)
70 {
71 	const struct canfd_frame *cf = (const struct canfd_frame *)skb->data;
72 	u8 len;
73 
74 	if (can_is_canfd_skb(skb))
75 		len = canfd_sanitize_len(cf->len);
76 	else if (cf->can_id & CAN_RTR_FLAG)
77 		len = 0;
78 	else
79 		len = cf->len;
80 
81 	if (can_is_canfd_skb(skb)) {
82 		if (cf->can_id & CAN_EFF_FLAG)
83 			len += CANFD_FRAME_OVERHEAD_EFF;
84 		else
85 			len += CANFD_FRAME_OVERHEAD_SFF;
86 	} else {
87 		if (cf->can_id & CAN_EFF_FLAG)
88 			len += CAN_FRAME_OVERHEAD_EFF;
89 		else
90 			len += CAN_FRAME_OVERHEAD_SFF;
91 	}
92 
93 	return len;
94 }
95 EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
96