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SubjectRe: [PATCH v3 5/7] can: dev: add a helper function to calculate the duration of one bit
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On 10/2/20 5:41 PM, Vincent Mailhol wrote:
> 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>
> ---
>
> Changes in v3: None
>
> Changes in v2: None
> ---
> 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 791c452d98e1..77c3ea49b8fb 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)

make it return an unsigned int
make the bt pointer const

> +{
> + 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.
>

tnx,
Marc

--
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Embedded Linux | https://www.pengutronix.de |
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