// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (C) 2005 Marc Kleine-Budde, Pengutronix
 * Copyright (C) 2006 Andrey Volkov, Varma Electronics
 * Copyright (C) 2008-2009 Wolfgang Grandegger <wg@grandegger.com>
 * Copyright (C) 2021-2025 Vincent Mailhol <mailhol@kernel.org>
 */

#include <linux/units.h>
#include <linux/can/dev.h>

#define CAN_CALC_MAX_ERROR 500 /* max error 5% */

/* CiA recommended sample points for Non Return to Zero encoding. */
static int can_calc_sample_point_nrz(const struct can_bittiming *bt)
{
        if (bt->bitrate > 800 * KILO /* BPS */)
                return 750;

        if (bt->bitrate > 500 * KILO /* BPS */)
                return 800;

        return 875;
}

/* Sample points for Pulse-Width Modulation encoding. */
static int can_calc_sample_point_pwm(const struct can_bittiming *bt)
{
        if (bt->bitrate > 15 * MEGA /* BPS */)
                return 625;

        if (bt->bitrate > 9 * MEGA /* BPS */)
                return 600;

        if (bt->bitrate > 4 * MEGA /* BPS */)
                return 560;

        return 520;
}

/* Bit-timing calculation derived from:
 *
 * Code based on LinCAN sources and H8S2638 project
 * Copyright 2004-2006 Pavel Pisa - DCE FELK CVUT cz
 * Copyright 2005      Stanislav Marek
 * email: pisa@cmp.felk.cvut.cz
 *
 * Calculates proper bit-timing parameters for a specified bit-rate
 * and sample-point, which can then be used to set the bit-timing
 * registers of the CAN controller. You can find more information
 * in the header file linux/can/netlink.h.
 */
static int
can_update_sample_point(const struct can_bittiming_const *btc,
                        const unsigned int sample_point_reference, const unsigned int tseg,
                        unsigned int *tseg1_ptr, unsigned int *tseg2_ptr,
                        unsigned int *sample_point_error_ptr)
{
        unsigned int sample_point_error, best_sample_point_error = UINT_MAX;
        unsigned int sample_point, best_sample_point = 0;
        unsigned int tseg1, tseg2;
        int i;

        for (i = 0; i <= 1; i++) {
                tseg2 = tseg + CAN_SYNC_SEG -
                        (sample_point_reference * (tseg + CAN_SYNC_SEG)) /
                        1000 - i;
                tseg2 = clamp(tseg2, btc->tseg2_min, btc->tseg2_max);
                tseg1 = tseg - tseg2;
                if (tseg1 > btc->tseg1_max) {
                        tseg1 = btc->tseg1_max;
                        tseg2 = tseg - tseg1;
                }

                sample_point = 1000 * (tseg + CAN_SYNC_SEG - tseg2) /
                        (tseg + CAN_SYNC_SEG);
                sample_point_error = abs(sample_point_reference - sample_point);

                if (sample_point <= sample_point_reference &&
                    sample_point_error < best_sample_point_error) {
                        best_sample_point = sample_point;
                        best_sample_point_error = sample_point_error;
                        *tseg1_ptr = tseg1;
                        *tseg2_ptr = tseg2;
                }
        }

        if (sample_point_error_ptr)
                *sample_point_error_ptr = best_sample_point_error;

        return best_sample_point;
}

int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
                       const struct can_bittiming_const *btc, struct netlink_ext_ack *extack)
{
        struct can_priv *priv = netdev_priv(dev);
        unsigned int bitrate;                   /* current bitrate */
        unsigned int bitrate_error;             /* diff between calculated and reference value */
        unsigned int best_bitrate_error = UINT_MAX;
        unsigned int sample_point_error;        /* diff between calculated and reference value */
        unsigned int best_sample_point_error = UINT_MAX;
        unsigned int sample_point_reference;    /* reference sample point */
        unsigned int best_tseg = 0;             /* current best value for tseg */
        unsigned int best_brp = 0;              /* current best value for brp */
        unsigned int brp, tsegall, tseg, tseg1 = 0, tseg2 = 0;
        u64 v64;
        int err;

        if (bt->sample_point)
                sample_point_reference = bt->sample_point;
        else if (btc == priv->xl.data_bittiming_const &&
                 (priv->ctrlmode & CAN_CTRLMODE_XL_TMS))
                sample_point_reference = can_calc_sample_point_pwm(bt);
        else
                sample_point_reference = can_calc_sample_point_nrz(bt);

        /* tseg even = round down, odd = round up */
        for (tseg = (btc->tseg1_max + btc->tseg2_max) * 2 + 1;
             tseg >= (btc->tseg1_min + btc->tseg2_min) * 2; tseg--) {
                tsegall = CAN_SYNC_SEG + tseg / 2;

                /* Compute all possible tseg choices (tseg=tseg1+tseg2) */
                brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2;

                /* choose brp step which is possible in system */
                brp = (brp / btc->brp_inc) * btc->brp_inc;
                if (brp < btc->brp_min || brp > btc->brp_max)
                        continue;

                bitrate = priv->clock.freq / (brp * tsegall);
                bitrate_error = abs(bt->bitrate - bitrate);

                /* tseg brp biterror */
                if (bitrate_error > best_bitrate_error)
                        continue;

                /* reset sample point error if we have a better bitrate */
                if (bitrate_error < best_bitrate_error)
                        best_sample_point_error = UINT_MAX;

                can_update_sample_point(btc, sample_point_reference, tseg / 2,
                                        &tseg1, &tseg2, &sample_point_error);
                if (sample_point_error >= best_sample_point_error)
                        continue;

                best_sample_point_error = sample_point_error;
                best_bitrate_error = bitrate_error;
                best_tseg = tseg / 2;
                best_brp = brp;

                if (bitrate_error == 0 && sample_point_error == 0)
                        break;
        }

        if (best_bitrate_error) {
                /* Error in one-hundredth of a percent */
                v64 = (u64)best_bitrate_error * 10000;
                do_div(v64, bt->bitrate);
                bitrate_error = (u32)v64;
                /* print at least 0.01% if the error is smaller */
                bitrate_error = max(bitrate_error, 1U);
                if (bitrate_error > CAN_CALC_MAX_ERROR) {
                        NL_SET_ERR_MSG_FMT(extack,
                                           "bitrate error: %u.%02u%% too high",
                                           bitrate_error / 100,
                                           bitrate_error % 100);
                        return -EINVAL;
                }
                NL_SET_ERR_MSG_FMT(extack,
                                   "bitrate error: %u.%02u%%",
                                   bitrate_error / 100, bitrate_error % 100);
        }

        /* real sample point */
        bt->sample_point = can_update_sample_point(btc, sample_point_reference,
                                                   best_tseg, &tseg1, &tseg2,
                                                   NULL);

        v64 = (u64)best_brp * 1000 * 1000 * 1000;
        do_div(v64, priv->clock.freq);
        bt->tq = (u32)v64;
        bt->prop_seg = tseg1 / 2;
        bt->phase_seg1 = tseg1 - bt->prop_seg;
        bt->phase_seg2 = tseg2;

        can_sjw_set_default(bt);

        err = can_sjw_check(dev, bt, btc, extack);
        if (err)
                return err;

        bt->brp = best_brp;

        /* real bitrate */
        bt->bitrate = priv->clock.freq /
                (bt->brp * can_bit_time(bt));

        return 0;
}

void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
                   const struct can_bittiming *dbt,
                   u32 tdc_mask, u32 *ctrlmode, u32 ctrlmode_supported)

{
        u32 tdc_auto = tdc_mask & CAN_CTRLMODE_TDC_AUTO_MASK;

        if (!tdc_const || !(ctrlmode_supported & tdc_auto))
                return;

        *ctrlmode &= ~tdc_mask;

        /* As specified in ISO 11898-1 section 11.3.3 "Transmitter
         * delay compensation" (TDC) is only applicable if data BRP is
         * one or two.
         */
        if (dbt->brp == 1 || dbt->brp == 2) {
                /* Sample point in clock periods */
                u32 sample_point_in_tc = (CAN_SYNC_SEG + dbt->prop_seg +
                                          dbt->phase_seg1) * dbt->brp;

                if (sample_point_in_tc < tdc_const->tdco_min)
                        return;
                tdc->tdco = min(sample_point_in_tc, tdc_const->tdco_max);
                *ctrlmode |= tdc_auto;
        }
}

int can_calc_pwm(struct net_device *dev, struct netlink_ext_ack *extack)
{
        struct can_priv *priv = netdev_priv(dev);
        const struct can_pwm_const *pwm_const = priv->xl.pwm_const;
        struct can_pwm *pwm = &priv->xl.pwm;
        u32 xl_tqmin = can_bit_time_tqmin(&priv->xl.data_bittiming);
        u32 xl_ns = can_tqmin_to_ns(xl_tqmin, priv->clock.freq);
        u32 nom_tqmin = can_bit_time_tqmin(&priv->bittiming);
        int pwm_per_bit_max = xl_tqmin / (pwm_const->pwms_min + pwm_const->pwml_min);
        int pwm_per_bit;
        u32 pwm_tqmin;

        /* For 5 MB/s databitrate or greater, xl_ns < CAN_PWM_NS_MAX
         * giving us a pwm_per_bit of 1 and the loop immediately breaks
         */
        for (pwm_per_bit = DIV_ROUND_UP(xl_ns, CAN_PWM_NS_MAX);
             pwm_per_bit <= pwm_per_bit_max; pwm_per_bit++)
                if (xl_tqmin % pwm_per_bit == 0)
                        break;

        if (pwm_per_bit > pwm_per_bit_max) {
                NL_SET_ERR_MSG_FMT(extack,
                                   "Can not divide the XL data phase's bit time: %u tqmin into multiple PWM symbols",
                                   xl_tqmin);
                return -EINVAL;
        }

        pwm_tqmin = xl_tqmin / pwm_per_bit;
        pwm->pwms = DIV_ROUND_UP_POW2(pwm_tqmin, 4);
        pwm->pwml = pwm_tqmin - pwm->pwms;
        pwm->pwmo = nom_tqmin % pwm_tqmin;

        return 0;
}