can: m_can: Reset coalescing during suspend/resume

During resume the interrupts are limited to IR_RF0N and the chip keeps
running. In this case if coalescing is enabled and active we may miss
waterlevel interrupts during suspend. It is safer to reset the
coalescing by stopping the timer and adding IR_RF0N | IR_TEFN to the
interrupts.

This is a theoratical issue and probably extremely rare.

Cc: Martin Hundebøll <martin@geanix.com>
Fixes: 4a94d7e3 ("can: m_can: allow keeping the transceiver running in suspend")
Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Link: https://lore.kernel.org/all/20240805183047.305630-2-msp@baylibre.comSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can.c

@@ -2430,12 +2430,15 @@ int m_can_class_suspend(struct device *dev)
 		netif_device_detach(ndev);
 
 		/* leave the chip running with rx interrupt enabled if it is
-		 * used as a wake-up source.
+		 * used as a wake-up source. Coalescing needs to be reset then,
+		 * the timer is cancelled here, interrupts are done in resume.
 		 */
-		if (cdev->pm_wake_source)
+		if (cdev->pm_wake_source) {
+			hrtimer_cancel(&cdev->hrtimer);
 			m_can_write(cdev, M_CAN_IE, IR_RF0N);
-		else
+		} else {
 			m_can_stop(ndev);
+		}
 
 		m_can_clk_stop(cdev);
 	}
@@ -2465,6 +2468,13 @@ int m_can_class_resume(struct device *dev)
 			return ret;
 
 		if (cdev->pm_wake_source) {
+			/* Restore active interrupts but disable coalescing as
+			 * we may have missed important waterlevel interrupts
+			 * between suspend and resume. Timers are already
+			 * stopped in suspend. Here we enable all interrupts
+			 * again.
+			 */
+			cdev->active_interrupts |= IR_RF0N | IR_TEFN;
 			m_can_write(cdev, M_CAN_IE, cdev->active_interrupts);
 		} else {
 			ret  = m_can_start(ndev);