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can: add new CAN FD bittiming parameters: Transmitter Delay Compensation (TDC)

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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: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
This commit is contained in:
Vincent Mailhol 2021-02-24 09:20:04 +09:00 committed by Marc Kleine-Budde
parent f318482a1c
commit 289ea9e4ae
2 changed files with 68 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

65
include/linux/can/bittiming.h
View file

@ -1,5 +1,6 @@
/* 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);

3
include/linux/can/dev.h
View file

@ -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;