drivers/net/can/dev/bittiming.c - linux - Git at Google

 // 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>
  */

 #include <linux/can/dev.h>

 #ifdef CONFIG_CAN_CALC_BITTIMING
 #define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */

 /* 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,
 			unsigned int sample_point_nominal, 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_nominal * (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_nominal - sample_point);

 		if (sample_point <= sample_point_nominal &&
 		    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(struct net_device *dev, struct can_bittiming *bt,
 		       const struct can_bittiming_const *btc)
 {
 	struct can_priv *priv = netdev_priv(dev);
 	unsigned int bitrate;			/* current bitrate */
 	unsigned int bitrate_error;		/* difference between current and nominal value */
 	unsigned int best_bitrate_error = UINT_MAX;
 	unsigned int sample_point_error;	/* difference between current and nominal value */
 	unsigned int best_sample_point_error = UINT_MAX;
 	unsigned int sample_point_nominal;	/* nominal 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;

 	/* Use CiA recommended sample points */
 	if (bt->sample_point) {
 		sample_point_nominal = bt->sample_point;
 	} else {
 		if (bt->bitrate > 800 * CAN_KBPS)
 			sample_point_nominal = 750;
 		else if (bt->bitrate > 500 * CAN_KBPS)
 			sample_point_nominal = 800;
 		else
 			sample_point_nominal = 875;
 	}

 	/* 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_nominal, 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-tenth of a percent */
 		v64 = (u64)best_bitrate_error * 1000;
 		do_div(v64, bt->bitrate);
 		bitrate_error = (u32)v64;
 		if (bitrate_error > CAN_CALC_MAX_ERROR) {
 			netdev_err(dev,
 				   "bitrate error %d.%d%% too high\n",
 				   bitrate_error / 10, bitrate_error % 10);
 			return -EDOM;
 		}
 		netdev_warn(dev, "bitrate error %d.%d%%\n",
 			    bitrate_error / 10, bitrate_error % 10);
 	}

 	/* real sample point */
 	bt->sample_point = can_update_sample_point(btc, sample_point_nominal,
 						   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;

 	/* check for sjw user settings */
 	if (!bt->sjw || !btc->sjw_max) {
 		bt->sjw = 1;
 	} else {
 		/* bt->sjw is at least 1 -> sanitize upper bound to sjw_max */
 		if (bt->sjw > btc->sjw_max)
 			bt->sjw = btc->sjw_max;
 		/* bt->sjw must not be higher than tseg2 */
 		if (tseg2 < bt->sjw)
 			bt->sjw = tseg2;
 	}

 	bt->brp = best_brp;

 	/* real bitrate */
 	bt->bitrate = priv->clock.freq /
 		(bt->brp * (CAN_SYNC_SEG + tseg1 + tseg2));

 	return 0;
 }

 void can_calc_tdco(struct net_device *dev)
 {
 	struct can_priv *priv = netdev_priv(dev);
 	const struct can_bittiming *dbt = &priv->data_bittiming;
 	struct can_tdc *tdc = &priv->tdc;
 	const struct can_tdc_const *tdc_const = priv->tdc_const;

 	if (!tdc_const)
 		return;

 	/* 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) {
 		/* Reuse "normal" sample point and convert it to time quanta */
 		u32 sample_point_in_tq = can_bit_time(dbt) * dbt->sample_point / 1000;

 		tdc->tdco = min(sample_point_in_tq, tdc_const->tdco_max);
 	} else {
 		tdc->tdco = 0;
 	}
 }
 #endif /* CONFIG_CAN_CALC_BITTIMING */

 /* Checks the validity of the specified bit-timing parameters prop_seg,
  * phase_seg1, phase_seg2 and sjw and tries to determine the bitrate
  * prescaler value brp. You can find more information in the header
  * file linux/can/netlink.h.
  */
 static int can_fixup_bittiming(struct net_device *dev, struct can_bittiming *bt,
 			       const struct can_bittiming_const *btc)
 {
 	struct can_priv *priv = netdev_priv(dev);
 	int tseg1, alltseg;
 	u64 brp64;

 	tseg1 = bt->prop_seg + bt->phase_seg1;
 	if (!bt->sjw)
 		bt->sjw = 1;
 	if (bt->sjw > btc->sjw_max ||
 	    tseg1 < btc->tseg1_min || tseg1 > btc->tseg1_max ||
 	    bt->phase_seg2 < btc->tseg2_min || bt->phase_seg2 > btc->tseg2_max)
 		return -ERANGE;

 	brp64 = (u64)priv->clock.freq * (u64)bt->tq;
 	if (btc->brp_inc > 1)
 		do_div(brp64, btc->brp_inc);
 	brp64 += 500000000UL - 1;
 	do_div(brp64, 1000000000UL); /* the practicable BRP */
 	if (btc->brp_inc > 1)
 		brp64 *= btc->brp_inc;
 	bt->brp = (u32)brp64;

 	if (bt->brp < btc->brp_min || bt->brp > btc->brp_max)
 		return -EINVAL;

 	alltseg = bt->prop_seg + bt->phase_seg1 + bt->phase_seg2 + 1;
 	bt->bitrate = priv->clock.freq / (bt->brp * alltseg);
 	bt->sample_point = ((tseg1 + 1) * 1000) / alltseg;

 	return 0;
 }

 /* Checks the validity of predefined bitrate settings */
 static int
 can_validate_bitrate(struct net_device *dev, struct can_bittiming *bt,
 		     const u32 *bitrate_const,
 		     const unsigned int bitrate_const_cnt)
 {
 	struct can_priv *priv = netdev_priv(dev);
 	unsigned int i;

 	for (i = 0; i < bitrate_const_cnt; i++) {
 		if (bt->bitrate == bitrate_const[i])
 			break;
 	}

 	if (i >= priv->bitrate_const_cnt)
 		return -EINVAL;

 	return 0;
 }

 int can_get_bittiming(struct net_device *dev, struct can_bittiming *bt,
 		      const struct can_bittiming_const *btc,
 		      const u32 *bitrate_const,
 		      const unsigned int bitrate_const_cnt)
 {
 	int err;

 	/* Depending on the given can_bittiming parameter structure the CAN
 	 * timing parameters are calculated based on the provided bitrate OR
 	 * alternatively the CAN timing parameters (tq, prop_seg, etc.) are
 	 * provided directly which are then checked and fixed up.
 	 */
 	if (!bt->tq && bt->bitrate && btc)
 		err = can_calc_bittiming(dev, bt, btc);
 	else if (bt->tq && !bt->bitrate && btc)
 		err = can_fixup_bittiming(dev, bt, btc);
 	else if (!bt->tq && bt->bitrate && bitrate_const)
 		err = can_validate_bitrate(dev, bt, bitrate_const,
 					   bitrate_const_cnt);
 	else
 		err = -EINVAL;

 	return err;
 }
	// 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>
	*/

	#include <linux/can/dev.h>

	#ifdef CONFIG_CAN_CALC_BITTIMING
	#define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */

	/* 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,
	unsigned int sample_point_nominal, 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_nominal * (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_nominal - sample_point);

	if (sample_point <= sample_point_nominal &&
	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(struct net_device dev, struct can_bittiming bt,
	const struct can_bittiming_const *btc)
	{
	struct can_priv *priv = netdev_priv(dev);
	unsigned int bitrate; /* current bitrate */
	unsigned int bitrate_error; /* difference between current and nominal value */
	unsigned int best_bitrate_error = UINT_MAX;
	unsigned int sample_point_error; /* difference between current and nominal value */
	unsigned int best_sample_point_error = UINT_MAX;
	unsigned int sample_point_nominal; /* nominal 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;

	/* Use CiA recommended sample points */
	if (bt->sample_point) {
	sample_point_nominal = bt->sample_point;
	} else {
	if (bt->bitrate > 800 * CAN_KBPS)
	sample_point_nominal = 750;
	else if (bt->bitrate > 500 * CAN_KBPS)
	sample_point_nominal = 800;
	else
	sample_point_nominal = 875;
	}

	/* 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_nominal, 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-tenth of a percent */
	v64 = (u64)best_bitrate_error * 1000;
	do_div(v64, bt->bitrate);
	bitrate_error = (u32)v64;
	if (bitrate_error > CAN_CALC_MAX_ERROR) {
	netdev_err(dev,
	"bitrate error %d.%d%% too high\n",
	bitrate_error / 10, bitrate_error % 10);
	return -EDOM;
	}
	netdev_warn(dev, "bitrate error %d.%d%%\n",
	bitrate_error / 10, bitrate_error % 10);
	}

	/* real sample point */
	bt->sample_point = can_update_sample_point(btc, sample_point_nominal,
	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;

	/* check for sjw user settings */
	if (!bt->sjw \|\| !btc->sjw_max) {
	bt->sjw = 1;
	} else {
	/* bt->sjw is at least 1 -> sanitize upper bound to sjw_max */
	if (bt->sjw > btc->sjw_max)
	bt->sjw = btc->sjw_max;
	/* bt->sjw must not be higher than tseg2 */
	if (tseg2 < bt->sjw)
	bt->sjw = tseg2;
	}

	bt->brp = best_brp;

	/* real bitrate */
	bt->bitrate = priv->clock.freq /
	(bt->brp * (CAN_SYNC_SEG + tseg1 + tseg2));

	return 0;
	}

	void can_calc_tdco(struct net_device *dev)
	{
	struct can_priv *priv = netdev_priv(dev);
	const struct can_bittiming *dbt = &priv->data_bittiming;
	struct can_tdc *tdc = &priv->tdc;
	const struct can_tdc_const *tdc_const = priv->tdc_const;

	if (!tdc_const)
	return;

	/* 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) {
	/* Reuse "normal" sample point and convert it to time quanta */
	u32 sample_point_in_tq = can_bit_time(dbt) * dbt->sample_point / 1000;

	tdc->tdco = min(sample_point_in_tq, tdc_const->tdco_max);
	} else {
	tdc->tdco = 0;
	}
	}
	#endif /* CONFIG_CAN_CALC_BITTIMING */

	/* Checks the validity of the specified bit-timing parameters prop_seg,
	* phase_seg1, phase_seg2 and sjw and tries to determine the bitrate
	* prescaler value brp. You can find more information in the header
	* file linux/can/netlink.h.
	*/
	static int can_fixup_bittiming(struct net_device dev, struct can_bittiming bt,
	const struct can_bittiming_const *btc)
	{
	struct can_priv *priv = netdev_priv(dev);
	int tseg1, alltseg;
	u64 brp64;

	tseg1 = bt->prop_seg + bt->phase_seg1;
	if (!bt->sjw)
	bt->sjw = 1;
	if (bt->sjw > btc->sjw_max \|\|
	tseg1 < btc->tseg1_min \|\| tseg1 > btc->tseg1_max \|\|
	bt->phase_seg2 < btc->tseg2_min \|\| bt->phase_seg2 > btc->tseg2_max)
	return -ERANGE;

	brp64 = (u64)priv->clock.freq * (u64)bt->tq;
	if (btc->brp_inc > 1)
	do_div(brp64, btc->brp_inc);
	brp64 += 500000000UL - 1;
	do_div(brp64, 1000000000UL); /* the practicable BRP */
	if (btc->brp_inc > 1)
	brp64 *= btc->brp_inc;
	bt->brp = (u32)brp64;

	if (bt->brp < btc->brp_min \|\| bt->brp > btc->brp_max)
	return -EINVAL;

	alltseg = bt->prop_seg + bt->phase_seg1 + bt->phase_seg2 + 1;
	bt->bitrate = priv->clock.freq / (bt->brp * alltseg);
	bt->sample_point = ((tseg1 + 1) * 1000) / alltseg;

	return 0;
	}

	/* Checks the validity of predefined bitrate settings */
	static int
	can_validate_bitrate(struct net_device dev, struct can_bittiming bt,
	const u32 *bitrate_const,
	const unsigned int bitrate_const_cnt)
	{
	struct can_priv *priv = netdev_priv(dev);
	unsigned int i;

	for (i = 0; i < bitrate_const_cnt; i++) {
	if (bt->bitrate == bitrate_const[i])
	break;
	}

	if (i >= priv->bitrate_const_cnt)
	return -EINVAL;

	return 0;
	}

	int can_get_bittiming(struct net_device dev, struct can_bittiming bt,
	const struct can_bittiming_const *btc,
	const u32 *bitrate_const,
	const unsigned int bitrate_const_cnt)
	{
	int err;

	/* Depending on the given can_bittiming parameter structure the CAN
	* timing parameters are calculated based on the provided bitrate OR
	* alternatively the CAN timing parameters (tq, prop_seg, etc.) are
	* provided directly which are then checked and fixed up.
	*/
	if (!bt->tq && bt->bitrate && btc)
	err = can_calc_bittiming(dev, bt, btc);
	else if (bt->tq && !bt->bitrate && btc)
	err = can_fixup_bittiming(dev, bt, btc);
	else if (!bt->tq && bt->bitrate && bitrate_const)
	err = can_validate_bitrate(dev, bt, bitrate_const,
	bitrate_const_cnt);
	else
	err = -EINVAL;

	return err;
	}