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: 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>

Author: vincent-mailhol

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;
 }

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 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.