Commit 85d99c3e authored by Vincent Mailhol's avatar Vincent Mailhol Committed by Marc Kleine-Budde
Browse files

can: length: can_skb_get_frame_len(): introduce function to get data length of... 


can: length: can_skb_get_frame_len(): introduce function to get data 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: default avatarArunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Signed-off-by: default avatarArunachalam Santhanam <arunachalam.santhanam@in.bosch.com>
Co-developed-by: default avatarVincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: default avatarVincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: default avatarVincent Mailhol <mailhol.vincent@wanadoo.fr>
Reviewed-by: default avatarVincent Mailhol <mailhol.vincent@wanadoo.fr>
Co-developed-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20210111141930.693847-11-mkl@pengutronix.de


Signed-off-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
parent 99b7beb0

drivers/net/can/dev/length.c

+50 −0
Original line number Diff line number Diff line
@@ -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);

include/linux/can/length.h

+120 −0
Original line number Diff line number Diff line 
/* 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.
@@ -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)

{