can: flexcan: flexcan_chip_start(): enable loopback mode in flexcan

Self reception disable bit needs to be cleared for loopback mode to work
in flexcan.

Signed-off-by: Pankaj Bansal <pankaj.bansal@nxp.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/flexcan.c

@@ -995,7 +995,6 @@ static int flexcan_chip_start(struct net_device *dev)
 	 * halt now
 	 * only supervisor access
 	 * enable warning int
-	 * disable local echo
 	 * enable individual RX masking
 	 * choose format C
 	 * set max mailbox number
@@ -1003,8 +1002,8 @@ static int flexcan_chip_start(struct net_device *dev)
 	reg_mcr = priv->read(&regs->mcr);
 	reg_mcr &= ~FLEXCAN_MCR_MAXMB(0xff);
 	reg_mcr |= FLEXCAN_MCR_FRZ | FLEXCAN_MCR_HALT | FLEXCAN_MCR_SUPV |
-		FLEXCAN_MCR_WRN_EN | FLEXCAN_MCR_SRX_DIS | FLEXCAN_MCR_IRMQ |
-		FLEXCAN_MCR_IDAM_C | FLEXCAN_MCR_MAXMB(FLEXCAN_TX_MB);
+		FLEXCAN_MCR_WRN_EN | FLEXCAN_MCR_IRMQ | FLEXCAN_MCR_IDAM_C |
+		FLEXCAN_MCR_MAXMB(FLEXCAN_TX_MB);
 
 	/* MCR
 	 *
@@ -1017,6 +1016,23 @@ static int flexcan_chip_start(struct net_device *dev)
 	else
 		reg_mcr |= FLEXCAN_MCR_FEN;
 
+	/* MCR
+	 *
+	 * NOTE: In loopback mode, the CAN_MCR[SRXDIS] cannot be
+	 *       asserted because this will impede the self reception
+	 *       of a transmitted message. This is not documented in
+	 *       earlier versions of flexcan block guide.
+	 *
+	 * Self Reception:
+	 * - enable Self Reception for loopback mode
+	 *   (by clearing "Self Reception Disable" bit)
+	 * - disable for normal operation
+	 */
+	if (priv->can.ctrlmode & CAN_CTRLMODE_LOOPBACK)
+		reg_mcr &= ~FLEXCAN_MCR_SRX_DIS;
+	else
+		reg_mcr |= FLEXCAN_MCR_SRX_DIS;
+
 	netdev_dbg(dev, "%s: writing mcr=0x%08x", __func__, reg_mcr);
 	priv->write(reg_mcr, &regs->mcr);