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
9static 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) */
15u8 can_fd_dlc2len(u8 dlc)
16{
17 return dlc2len[dlc & 0x0F];
18}
19EXPORT_SYMBOL_GPL(can_fd_dlc2len);
20
21static 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 */
35u8 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}
45EXPORT_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 */
69unsigned 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(len: cf->len);
76 else if (cf->can_id & CAN_RTR_FLAG)
77 len = 0;
78 else
79 len = cf->len;
80
81 return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id & CAN_EFF_FLAG,
82 false, len);
83}
84EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
85

source code of linux/drivers/net/can/dev/length.c