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>

diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index 3c40bba71d5b6e16396eae455d3f2ae993f74718..b70ded3760f28cdb65d9372b4b0cf26f3afdc567 100644 (file)
--- 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 f8975d0b90bb8cb9520769e59d39fa28e6002366..41ff317953201d5cac941ece2a72273c745570ca 100644 (file)
--- 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 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.