drivers/net/can/dev/length.c

   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) */
  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 */
  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  */
  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         return can_frame_bytes(can_is_canfd_skb(skb), cf->can_id & CAN_EFF_FLAG,
  82                                false, len);
  83 }
  84 EXPORT_SYMBOL_GPL(can_skb_get_frame_len);