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Subject[PATCH 4/6] can: dev: add a helper function to calculate the duration of one bit
Date
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>
---
drivers/net/can/dev.c | 13 ++++++-------
include/linux/can/dev.h | 15 +++++++++++++++
2 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 8c3e11820e03..6070b4ab3bd8 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -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;
}
diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 72a8a60c0094..30b327f1a4bd 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -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 int can_bit_time(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.
--
2.26.2
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