Commit 289ea9e4 authored by Vincent Mailhol's avatar Vincent Mailhol Committed by Marc Kleine-Budde
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can: add new CAN FD bittiming parameters: Transmitter Delay Compensation (TDC) 

At high bit rates, the propagation delay from the TX pin to the RX pin
of the transceiver causes measurement errors: the sample point on the
RX pin might occur on the previous bit.

This issue is addressed in ISO 11898-1 section 11.3.3 "Transmitter
delay compensation" (TDC).

This patch adds two new structures: can_tdc and can_tdc_const in order
to implement this TDC.

The structures are then added to can_priv.

A controller supports TDC if an only if can_priv::tdc_const is not
NULL.

TDC is active if and only if:
  - fd flag is on
  - can_priv::tdc.tdco is not zero.
It is the driver responsibility to check those two conditions are met.

No new controller modes are introduced (i.e. no CAN_CTRL_MODE_TDC) in
order not to be redundant with above logic.

The names of the parameters are chosen to match existing CAN
controllers specification. References:
  - Bosch C_CAN FD8:
https://www.bosch-semiconductors.com/media/ip_modules/pdf_2/c_can_fd8/users_manual_c_can_fd8_r210_1.pdf
  - Microchip CAN FD Controller Module:
http://ww1.microchip.com/downloads/en/DeviceDoc/MCP251XXFD-CAN-FD-Controller-Module-Family-Reference-Manual-20005678B.pdf
  - SAM E701/S70/V70/V71 Family:
https://www.mouser.com/datasheet/2/268/60001527A-1284321.pdf

Link: https://lore.kernel.org/r/20210224002008.4158-2-mailhol.vincent@wanadoo.fr


Signed-off-by: default avatarVincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
parent f318482a

include/linux/can/bittiming.h

+65 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0-only */

/* Copyright (c) 2020 Pengutronix, Marc Kleine-Budde <kernel@pengutronix.de>

 * Copyright (c) 2021 Vincent Mailhol <mailhol.vincent@wanadoo.fr>

 */



#ifndef _CAN_BITTIMING_H
@@ -10,6 +11,70 @@ 


#define CAN_SYNC_SEG 1



/*

 * struct can_tdc - CAN FD Transmission Delay Compensation parameters

 *

 * At high bit rates, the propagation delay from the TX pin to the RX

 * pin of the transceiver causes measurement errors: the sample point

 * on the RX pin might occur on the previous bit.

 *

 * To solve this issue, ISO 11898-1 introduces in section 11.3.3

 * "Transmitter delay compensation" a SSP (Secondary Sample Point)

 * equal to the distance, in time quanta, from the start of the bit

 * time on the TX pin to the actual measurement on the RX pin.

 *

 * This structure contains the parameters to calculate that SSP.

 *

 * @tdcv: Transmitter Delay Compensation Value. Distance, in time

 *	quanta, from when the bit is sent on the TX pin to when it is

 *	received on the RX pin of the transmitter. Possible options:

 *

 *	  O: automatic mode. The controller dynamically measure @tdcv

 *	  for each transmitted CAN FD frame.

 *

 *	  Other values: manual mode. Use the fixed provided value.

 *

 * @tdco: Transmitter Delay Compensation Offset. Offset value, in time

 *	quanta, defining the distance between the start of the bit

 *	reception on the RX pin of the transceiver and the SSP

 *	position such as SSP = @tdcv + @tdco.

 *

 *	If @tdco is zero, then TDC is disabled and both @tdcv and

 *	@tdcf should be ignored.

 *

 * @tdcf: Transmitter Delay Compensation Filter window. Defines the

 *	minimum value for the SSP position in time quanta. If SSP is

 *	less than @tdcf, then no delay compensations occur and the

 *	normal sampling point is used instead. The feature is enabled

 *	if and only if @tdcv is set to zero (automatic mode) and @tdcf

 *	is configured to a value greater than @tdco.

 */

struct can_tdc {

	u32 tdcv;

	u32 tdco;

	u32 tdcf;

};



/*

 * struct can_tdc_const - CAN hardware-dependent constant for

 *	Transmission Delay Compensation

 *

 * @tdcv_max: Transmitter Delay Compensation Value maximum value.

 *	Should be set to zero if the controller does not support

 *	manual mode for tdcv.

 * @tdco_max: Transmitter Delay Compensation Offset maximum value.

 *	Should not be zero. If the controller does not support TDC,

 *	then the pointer to this structure should be NULL.

 * @tdcf_max: Transmitter Delay Compensation Filter window maximum

 *	value. Should be set to zero if the controller does not

 *	support this feature.

 */

struct can_tdc_const {

	u32 tdcv_max;

	u32 tdco_max;

	u32 tdcf_max;

};



#ifdef CONFIG_CAN_CALC_BITTIMING

int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt,

		       const struct can_bittiming_const *btc);

include/linux/can/dev.h

+3 −0
Original line number Diff line number Diff line
@@ -42,6 +42,9 @@ struct can_priv { 
	struct can_bittiming bittiming, data_bittiming;

	const struct can_bittiming_const *bittiming_const,

		*data_bittiming_const;

	struct can_tdc tdc;

	const struct can_tdc_const *tdc_const;



	const u16 *termination_const;

	unsigned int termination_const_cnt;

	u16 termination;