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

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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: Vincent 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: Marc Kleine-Budde <mkl@pengutronix.de>
This commit is contained in:
Vincent Mailhol 2020-10-03 00:41:49 +09:00 committed by Marc Kleine-Budde
parent f55a52bb2c
commit 1c47fa6b31
2 changed files with 21 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
drivers/net/can/dev.c
View File

@ -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;
}

15
include/linux/can/dev.h
View File

@ -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.