can: m_can: is_lec_err(): clean up LEC error handling

The PSR register contains among other the error for the CAN
arbitration phase (LEC bits) and CAN data phase (DLEC bits).

Prepare is_lec_err() to be called with the (D)LEC value only instead
of the whole PSR register. While there rename LEC_UNUSED to
LEC_NO_CHANGE to match the latest M_CAN reference manual.

Link: https://lore.kernel.org/all/20221019211611.1605764-1-mkl@pengutronix.de
Reviewed-by: Chandrasekar Ramakrishnan <rcsekar@samsung.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/m_can/m_can.c

@@ -816,11 +816,9 @@ static void m_can_handle_other_err(struct net_device *dev, u32 irqstatus)
 		netdev_err(dev, "Message RAM access failure occurred\n");
 }
 
-static inline bool is_lec_err(u32 psr)
+static inline bool is_lec_err(u8 lec)
 {
-	psr &= LEC_UNUSED;
-
-	return psr && (psr != LEC_UNUSED);
+	return lec != LEC_NO_ERROR && lec != LEC_NO_CHANGE;
 }
 
 static inline bool m_can_is_protocol_err(u32 irqstatus)
@@ -875,9 +873,12 @@ static int m_can_handle_bus_errors(struct net_device *dev, u32 irqstatus,
 		work_done += m_can_handle_lost_msg(dev);
 
 	/* handle lec errors on the bus */
-	if ((cdev->can.ctrlmode & CAN_CTRLMODE_BERR_REPORTING) &&
-	    is_lec_err(psr))
-		work_done += m_can_handle_lec_err(dev, psr & LEC_UNUSED);
+	if (cdev->can.ctrlmode & CAN_CTRLMODE_BERR_REPORTING) {
+		u8 lec = FIELD_GET(PSR_LEC_MASK, psr);
+
+		if (is_lec_err(lec))
+			work_done += m_can_handle_lec_err(dev, lec);
+	}
 
 	/* handle protocol errors in arbitration phase */
 	if ((cdev->can.ctrlmode & CAN_CTRLMODE_BERR_REPORTING) &&

drivers/net/can/m_can/m_can.h

@@ -38,7 +38,7 @@ enum m_can_lec_type {
 	LEC_BIT1_ERROR,
 	LEC_BIT0_ERROR,
 	LEC_CRC_ERROR,
-	LEC_UNUSED,
+	LEC_NO_CHANGE,
 };
 
 enum m_can_mram_cfg {