can: calc_bittiming: add PWM calculation

Perform the PWM calculation according to CiA recommendations.

Note that for databitrates greater than 5 MBPS, tqmin is less than
CAN_PWM_NS_MAX (which is defined to 200 nano seconds), consequently,
the result of the division:

  DIV_ROUND_UP(xl_ns, CAN_PWM_NS_MAX)

is one and thus the for loop automatically stops on the first
iteration giving a single PWM symbol per bit as expected. Because of
that, there is no actual need for a separate conditional branch for
when the databitrate is greater than 5 MBPS.

Signed-off-by: Vincent Mailhol <mailhol@kernel.org>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://patch.msgid.link/20251126-canxl-v8-10-e7e3eb74f889@pengutronix.de
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

1 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/can/bittiming.h b/include/linux/can/bittiming.h
index 2504fafc72e4..726d909e87ce 100644
--- a/include/linux/can/bittiming.h
+++ b/include/linux/can/bittiming.h
@@ -180,6 +180,8 @@ int can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
 void can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
 		   const struct can_bittiming *dbt,
 		   u32 tdc_mask, u32 *ctrlmode, u32 ctrlmode_supported);
+
+int can_calc_pwm(struct net_device *dev, struct netlink_ext_ack *extack);
 #else /* !CONFIG_CAN_CALC_BITTIMING */
 static inline int
 can_calc_bittiming(const struct net_device *dev, struct can_bittiming *bt,
@@ -195,6 +197,14 @@ can_calc_tdco(struct can_tdc *tdc, const struct can_tdc_const *tdc_const,
 	      u32 tdc_mask, u32 *ctrlmode, u32 ctrlmode_supported)
 {
 }
+
+static inline int
+can_calc_pwm(struct net_device *dev, struct netlink_ext_ack *extack)
+{
+	NL_SET_ERR_MSG(extack,
+		       "bit-timing calculation not available: manually provide PWML and PWMS\n");
+	return -EINVAL;
+}
 #endif /* CONFIG_CAN_CALC_BITTIMING */
 
 void can_sjw_set_default(struct can_bittiming *bt);