can: m_can: m_can_chip_config(): enable and configure internal timestamps

This is a prerequisite for transitioning the m_can driver to rx-offload,
which works best with TX and RX timestamps.

The timestamps provided by M_CAN are 16-bit, timed according to the
nominal bit timing, and may be prescaled by a multiplier up to 16. We
choose the highest prescalar so that the timestamp wraps every 2^20 bit
times, or 209 ms at a bus speed of 5 Mbit/s. Timestamps will have a
precision of 16 bit times.

Link: https://lore.kernel.org/r/20210308102427.63916-3-torin@maxiluxsystems.com
Signed-off-by: Torin Cooper-Bennun <torin@maxiluxsystems.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can.c

@@ -1135,6 +1135,7 @@ static int m_can_set_bittiming(struct net_device *dev)
  *		- >= v3.1.x: TX FIFO is used
  * - configure mode
  * - setup bittiming
+ * - configure timestamp generation
  */
 static void m_can_chip_config(struct net_device *dev)
 {
@@ -1246,6 +1247,10 @@ static void m_can_chip_config(struct net_device *dev)
 	/* set bittiming params */
 	m_can_set_bittiming(dev);
 
+	/* enable internal timestamp generation, with a prescalar of 16. The
+	 * prescalar is applied to the nominal bit timing */
+	m_can_write(cdev, M_CAN_TSCC, FIELD_PREP(TSCC_TCP_MASK, 0xf));
+
 	m_can_config_endisable(cdev, false);
 
 	if (cdev->ops->init)