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can: length: can_skb_get_frame_len(): introduce function to get data …
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…length of frame in data link layer

This patch adds the function can_skb_get_frame_len() which returns the length
of a CAN frame on the data link layer, including Start-of-frame, Identifier,
various other bits, the actual data, the CRC, the End-of-frame, the Inter frame
spacing.

Co-developed-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Signed-off-by: Arunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Co-developed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Co-developed-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20210111141930.693847-11-mkl@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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Vincent Mailhol authored and Marc Kleine-Budde committed Jan 14, 2021
1 parent 99b7beb commit 85d99c3
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50 changes: 50 additions & 0 deletions drivers/net/can/dev/length.c
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Original file line number Diff line number Diff line change
Expand Up @@ -38,3 +38,53 @@ u8 can_fd_len2dlc(u8 len)
return len2dlc[len];
}
EXPORT_SYMBOL_GPL(can_fd_len2dlc);

/**
* can_skb_get_frame_len() - Calculate the CAN Frame length in bytes
* of a given skb.
* @skb: socket buffer of a CAN message.
*
* Do a rough calculation: bit stuffing is ignored and length in bits
* is rounded up to a length in bytes.
*
* Rationale: this function is to be used for the BQL functions
* (netdev_sent_queue() and netdev_completed_queue()) which expect a
* value in bytes. Just using skb->len is insufficient because it will
* return the constant value of CAN(FD)_MTU. Doing the bit stuffing
* calculation would be too expensive in term of computing resources
* for no noticeable gain.
*
* Remarks: The payload of CAN FD frames with BRS flag are sent at a
* different bitrate. Currently, the can-utils canbusload tool does
* not support CAN-FD yet and so we could not run any benchmark to
* measure the impact. There might be possible improvement here.
*
* Return: length in bytes.
*/
unsigned int can_skb_get_frame_len(const struct sk_buff *skb)
{
const struct canfd_frame *cf = (const struct canfd_frame *)skb->data;
u8 len;

if (can_is_canfd_skb(skb))
len = canfd_sanitize_len(cf->len);
else if (cf->can_id & CAN_RTR_FLAG)
len = 0;
else
len = cf->len;

if (can_is_canfd_skb(skb)) {
if (cf->can_id & CAN_EFF_FLAG)
len += CANFD_FRAME_OVERHEAD_EFF;
else
len += CANFD_FRAME_OVERHEAD_SFF;
} else {
if (cf->can_id & CAN_EFF_FLAG)
len += CAN_FRAME_OVERHEAD_EFF;
else
len += CAN_FRAME_OVERHEAD_SFF;
}

return len;
}
EXPORT_SYMBOL_GPL(can_skb_get_frame_len);
120 changes: 120 additions & 0 deletions include/linux/can/length.h
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Original file line number Diff line number Diff line change
@@ -1,10 +1,127 @@
/* SPDX-License-Identifier: GPL-2.0 */
/* Copyright (C) 2020 Oliver Hartkopp <socketcan@hartkopp.net>
* Copyright (C) 2020 Marc Kleine-Budde <kernel@pengutronix.de>
*/

#ifndef _CAN_LENGTH_H
#define _CAN_LENGTH_H

/*
* Size of a Classical CAN Standard Frame
*
* Name of Field Bits
* ---------------------------------------------------------
* Start-of-frame 1
* Identifier 11
* Remote transmission request (RTR) 1
* Identifier extension bit (IDE) 1
* Reserved bit (r0) 1
* Data length code (DLC) 4
* Data field 0...64
* CRC 15
* CRC delimiter 1
* ACK slot 1
* ACK delimiter 1
* End-of-frame (EOF) 7
* Inter frame spacing 3
*
* rounded up and ignoring bitstuffing
*/
#define CAN_FRAME_OVERHEAD_SFF DIV_ROUND_UP(47, 8)

/*
* Size of a Classical CAN Extended Frame
*
* Name of Field Bits
* ---------------------------------------------------------
* Start-of-frame 1
* Identifier A 11
* Substitute remote request (SRR) 1
* Identifier extension bit (IDE) 1
* Identifier B 18
* Remote transmission request (RTR) 1
* Reserved bits (r1, r0) 2
* Data length code (DLC) 4
* Data field 0...64
* CRC 15
* CRC delimiter 1
* ACK slot 1
* ACK delimiter 1
* End-of-frame (EOF) 7
* Inter frame spacing 3
*
* rounded up and ignoring bitstuffing
*/
#define CAN_FRAME_OVERHEAD_EFF DIV_ROUND_UP(67, 8)

/*
* Size of a CAN-FD Standard Frame
*
* Name of Field Bits
* ---------------------------------------------------------
* Start-of-frame 1
* Identifier 11
* Reserved bit (r1) 1
* Identifier extension bit (IDE) 1
* Flexible data rate format (FDF) 1
* Reserved bit (r0) 1
* Bit Rate Switch (BRS) 1
* Error Status Indicator (ESI) 1
* Data length code (DLC) 4
* Data field 0...512
* Stuff Bit Count (SBC) 0...16: 4 20...64:5
* CRC 0...16: 17 20...64:21
* CRC delimiter (CD) 1
* ACK slot (AS) 1
* ACK delimiter (AD) 1
* End-of-frame (EOF) 7
* Inter frame spacing 3
*
* assuming CRC21, rounded up and ignoring bitstuffing
*/
#define CANFD_FRAME_OVERHEAD_SFF DIV_ROUND_UP(61, 8)

/*
* Size of a CAN-FD Extended Frame
*
* Name of Field Bits
* ---------------------------------------------------------
* Start-of-frame 1
* Identifier A 11
* Substitute remote request (SRR) 1
* Identifier extension bit (IDE) 1
* Identifier B 18
* Reserved bit (r1) 1
* Flexible data rate format (FDF) 1
* Reserved bit (r0) 1
* Bit Rate Switch (BRS) 1
* Error Status Indicator (ESI) 1
* Data length code (DLC) 4
* Data field 0...512
* Stuff Bit Count (SBC) 0...16: 4 20...64:5
* CRC 0...16: 17 20...64:21
* CRC delimiter (CD) 1
* ACK slot (AS) 1
* ACK delimiter (AD) 1
* End-of-frame (EOF) 7
* Inter frame spacing 3
*
* assuming CRC21, rounded up and ignoring bitstuffing
*/
#define CANFD_FRAME_OVERHEAD_EFF DIV_ROUND_UP(80, 8)

/*
* Maximum size of a Classical CAN frame
* (rounded up and ignoring bitstuffing)
*/
#define CAN_FRAME_LEN_MAX (CAN_FRAME_OVERHEAD_EFF + CAN_MAX_DLEN)

/*
* Maximum size of a CAN-FD frame
* (rounded up and ignoring bitstuffing)
*/
#define CANFD_FRAME_LEN_MAX (CANFD_FRAME_OVERHEAD_EFF + CANFD_MAX_DLEN)

/*
* can_cc_dlc2len(value) - convert a given data length code (dlc) of a
* Classical CAN frame into a valid data length of max. 8 bytes.
Expand Down Expand Up @@ -45,6 +162,9 @@ u8 can_fd_dlc2len(u8 dlc);
/* map the sanitized data length to an appropriate data length code */
u8 can_fd_len2dlc(u8 len);

/* calculate the CAN Frame length in bytes of a given skb */
unsigned int can_skb_get_frame_len(const struct sk_buff *skb);

/* map the data length to an appropriate data link layer length */
static inline u8 canfd_sanitize_len(u8 len)
{
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