include/linux/can/bittiming.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /* Copyright (c) 2020 Pengutronix, Marc Kleine-Budde <kernel@pengutronix.de>
   3  * Copyright (c) 2021 Vincent Mailhol <mailhol.vincent@wanadoo.fr>
   4  */
   5
   6 #ifndef _CAN_BITTIMING_H
   7 #define _CAN_BITTIMING_H
   8
   9 #include <linux/netdevice.h>
  10 #include <linux/can/netlink.h>
  11
  12 #define CAN_SYNC_SEG 1
  13
  14 #define CAN_BITRATE_UNSET 0
  15 #define CAN_BITRATE_UNKNOWN (-1U)
  16
  17 #define CAN_CTRLMODE_TDC_MASK                                   \
  18         (CAN_CTRLMODE_TDC_AUTO | CAN_CTRLMODE_TDC_MANUAL)
  19
  20 /*
  21  * struct can_tdc - CAN FD Transmission Delay Compensation parameters
  22  *
  23  * At high bit rates, the propagation delay from the TX pin to the RX
  24  * pin of the transceiver causes measurement errors: the sample point
  25  * on the RX pin might occur on the previous bit.
  26  *
  27  * To solve this issue, ISO 11898-1 introduces in section 11.3.3
  28  * "Transmitter delay compensation" a SSP (Secondary Sample Point)
  29  * equal to the distance from the start of the bit time on the TX pin
  30  * to the actual measurement on the RX pin.
  31  *
  32  * This structure contains the parameters to calculate that SSP.
  33  *
  34  * -+----------- one bit ----------+-- TX pin
  35  *  |<--- Sample Point --->|
  36  *
  37  *                         --+----------- one bit ----------+-- RX pin
  38  *  |<-------- TDCV -------->|
  39  *                           |<------- TDCO ------->|
  40  *  |<----------- Secondary Sample Point ---------->|
  41  *
  42  * To increase precision, contrary to the other bittiming parameters
  43  * which are measured in time quanta, the TDC parameters are measured
  44  * in clock periods (also referred as "minimum time quantum" in ISO
  45  * 11898-1).
  46  *
  47  * @tdcv: Transmitter Delay Compensation Value. The time needed for
  48  *      the signal to propagate, i.e. the distance, in clock periods,
  49  *      from the start of the bit on the TX pin to when it is received
  50  *      on the RX pin. @tdcv depends on the controller modes:
  51  *
  52  *        CAN_CTRLMODE_TDC_AUTO is set: The transceiver dynamically
  53  *        measures @tdcv for each transmitted CAN FD frame and the
  54  *        value provided here should be ignored.
  55  *
  56  *        CAN_CTRLMODE_TDC_MANUAL is set: use the fixed provided @tdcv
  57  *        value.
  58  *
  59  *      N.B. CAN_CTRLMODE_TDC_AUTO and CAN_CTRLMODE_TDC_MANUAL are
  60  *      mutually exclusive. Only one can be set at a time. If both
  61  *      CAN_TDC_CTRLMODE_AUTO and CAN_TDC_CTRLMODE_MANUAL are unset,
  62  *      TDC is disabled and all the values of this structure should be
  63  *      ignored.
  64  *
  65  * @tdco: Transmitter Delay Compensation Offset. Offset value, in
  66  *      clock periods, defining the distance between the start of the
  67  *      bit reception on the RX pin of the transceiver and the SSP
  68  *      position such that SSP = @tdcv + @tdco.
  69  *
  70  * @tdcf: Transmitter Delay Compensation Filter window. Defines the
  71  *      minimum value for the SSP position in clock periods. If the
  72  *      SSP position is less than @tdcf, then no delay compensations
  73  *      occur and the normal sampling point is used instead. The
  74  *      feature is enabled if and only if @tdcv is set to zero
  75  *      (automatic mode) and @tdcf is configured to a value greater
  76  *      than @tdco.
  77  */
  78 struct can_tdc {
  79         u32 tdcv;
  80         u32 tdco;
  81         u32 tdcf;
  82 };
  83
  84 /*
  85  * struct can_tdc_const - CAN hardware-dependent constant for
  86  *      Transmission Delay Compensation
  87  *
  88  * @tdcv_min: Transmitter Delay Compensation Value minimum value. If
  89  *      the controller does not support manual mode for tdcv
  90  *      (c.f. flag CAN_CTRLMODE_TDC_MANUAL) then this value is
  91  *      ignored.
  92  * @tdcv_max: Transmitter Delay Compensation Value maximum value. If
  93  *      the controller does not support manual mode for tdcv
  94  *      (c.f. flag CAN_CTRLMODE_TDC_MANUAL) then this value is
  95  *      ignored.
  96  *
  97  * @tdco_min: Transmitter Delay Compensation Offset minimum value.
  98  * @tdco_max: Transmitter Delay Compensation Offset maximum value.
  99  *      Should not be zero. If the controller does not support TDC,
 100  *      then the pointer to this structure should be NULL.
 101  *
 102  * @tdcf_min: Transmitter Delay Compensation Filter window minimum
 103  *      value. If @tdcf_max is zero, this value is ignored.
 104  * @tdcf_max: Transmitter Delay Compensation Filter window maximum
 105  *      value. Should be set to zero if the controller does not
 106  *      support this feature.
 107  */
 108 struct can_tdc_const {
 109         u32 tdcv_min;
 110         u32 tdcv_max;
 111         u32 tdco_min;
 112         u32 tdco_max;
 113         u32 tdcf_min;
 114         u32 tdcf_max;
 115 };
 116
 117 #ifdef CONFIG_CAN_CALC_BITTIMING
 118 int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 119                        const struct can_bittiming_const *btc, struct netlink_ext_ack *extack);
 120
 121 void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
 122                    const struct can_bittiming *dbt,
 123                    u32 *ctrlmode, u32 ctrlmode_supported);
 124 #else /* !CONFIG_CAN_CALC_BITTIMING */
 125 static inline int
 126 can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 127                    const struct can_bittiming_const *btc, struct netlink_ext_ack *extack)
 128 {
 129         netdev_err(dev, "bit-timing calculation not available\n");
 130         return -EINVAL;
 131 }
 132
 133 static inline void
 134 can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
 135               const struct can_bittiming *dbt,
 136               u32 *ctrlmode, u32 ctrlmode_supported)
 137 {
 138 }
 139 #endif /* CONFIG_CAN_CALC_BITTIMING */
 140
 141 void can_sjw_set_default(struct can_bittiming *bt);
 142
 143 int can_sjw_check(const struct net_device *dev, const struct can_bittiming *bt,
 144                   const struct can_bittiming_const *btc, struct netlink_ext_ack *extack);
 145
 146 int can_get_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 147                       const struct can_bittiming_const *btc,
 148                       const u32 *bitrate_const,
 149                       const unsigned int bitrate_const_cnt,
 150                       struct netlink_ext_ack *extack);
 151
 152 /*
 153  * can_bit_time() - Duration of one bit
 154  *
 155  * Please refer to ISO 11898-1:2015, section 11.3.1.1 "Bit time" for
 156  * additional information.
 157  *
 158  * Return: the number of time quanta in one bit.
 159  */
 160 static inline unsigned int can_bit_time(const struct can_bittiming *bt)
 161 {
 162         return CAN_SYNC_SEG + bt->prop_seg + bt->phase_seg1 + bt->phase_seg2;
 163 }
 164
 165 #endif /* !_CAN_BITTIMING_H */