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 Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> --- include/linux/can/bittiming.h | 65 +++++++++++++++++++++++++++++++++++ include/linux/can/dev.h | 3 ++ 2 files changed, 68 insertions(+) diff --git a/include/linux/can/bittiming.h b/include/linux/can/bittiming.h index 707575c668f4..91bf9f8926a7 100644 --- a/include/linux/can/bittiming.h +++ b/include/linux/can/bittiming.h @@ -1,5 +1,6 @@ /* SPDX-License-Identifier: GPL-2.0-only */ /* Copyright (c) 2020 Pengutronix, Marc Kleine-Budde <kernel@xxxxxxxxxxxxxx> + * Copyright (c) 2021 Vincent Mailhol <mailhol.vincent@xxxxxxxxxx> */ #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 transmited 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); diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h index ac4d83a1ab81..4795da0eb949 100644 --- a/include/linux/can/dev.h +++ b/include/linux/can/dev.h @@ -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; -- 2.26.2
