Commit 1c47fa6b authored by Vincent Mailhol's avatar Vincent Mailhol Committed by Marc Kleine-Budde
Browse files

can: dev: add a helper function to calculate the duration of one bit 



Rename macro CAN_CALC_SYNC_SEG to CAN_SYNC_SEG and make it available
through include/linux/can/dev.h

Add an helper function can_bit_time() which returns the duration (in
time quanta) of one CAN bit.

Rationale for this patch: the sync segment and the bit time are two
concepts which are defined in the CAN ISO standard. Device drivers for
CAN might need those.

Please refer to ISO 11898-1:2015, section 11.3.1.1 "Bit time" for
additional information.

Signed-off-by: default avatarVincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/r/20201002154219.4887-6-mailhol.vincent@wanadoo.fr


[mkl: Let can_bit_time() return an unsinged int, make argument const]
Signed-off-by: default avatarMarc Kleine-Budde <mkl@pengutronix.de>
parent f55a52bb

drivers/net/can/dev.c

+6 −7
Original line number Diff line number Diff line
@@ -60,7 +60,6 @@ EXPORT_SYMBOL_GPL(can_len2dlc); 


#ifdef CONFIG_CAN_CALC_BITTIMING

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

#define CAN_CALC_SYNC_SEG 1



/* Bit-timing calculation derived from:

 *
@@ -86,8 +85,8 @@ can_update_sample_point(const struct can_bittiming_const *btc, 
	int i;



	for (i = 0; i <= 1; i++) {

		tseg2 = tseg + CAN_CALC_SYNC_SEG -

			(sample_point_nominal * (tseg + CAN_CALC_SYNC_SEG)) /

		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;
@@ -96,8 +95,8 @@ can_update_sample_point(const struct can_bittiming_const *btc, 
			tseg2 = tseg - tseg1;

		}



		sample_point = 1000 * (tseg + CAN_CALC_SYNC_SEG - tseg2) /

			(tseg + CAN_CALC_SYNC_SEG);

		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 &&
@@ -145,7 +144,7 @@ static int can_calc_bittiming(struct net_device *dev, struct can_bittiming *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_CALC_SYNC_SEG + tseg / 2;

		tsegall = CAN_SYNC_SEG + tseg / 2;



		/* Compute all possible tseg choices (tseg=tseg1+tseg2) */

		brp = priv->clock.freq / (tsegall * bt->bitrate) + tseg % 2;
@@ -223,7 +222,7 @@ static int can_calc_bittiming(struct net_device *dev, struct can_bittiming *bt, 


	/* real bitrate */

	bt->bitrate = priv->clock.freq /

		(bt->brp * (CAN_CALC_SYNC_SEG + tseg1 + tseg2));

		(bt->brp * (CAN_SYNC_SEG + tseg1 + tseg2));



	return 0;

}

include/linux/can/dev.h

+15 −0
Original line number Diff line number Diff line
@@ -82,6 +82,21 @@ struct can_priv { 
#endif

};



#define CAN_SYNC_SEG 1



/*

 * can_bit_time() - Duration of one bit

 *

 * Please refer to ISO 11898-1:2015, section 11.3.1.1 "Bit time" for

 * additional information.

 *

 * Return: the number of time quanta in one bit.

 */

static inline unsigned int can_bit_time(const struct can_bittiming *bt)

{

	return CAN_SYNC_SEG + bt->prop_seg + bt->phase_seg1 + bt->phase_seg2;

}



/*

 * get_can_dlc(value) - helper macro to cast a given data length code (dlc)

 * to u8 and ensure the dlc value to be max. 8 bytes.