can: mcp251xfd: Add support for internal loopback mode

MCP251xFD supports internal loopback mode which can be used to verify CAN
functionality in the absence of a real CAN device.

Link: https://lore.kernel.org/r/20201201054019.11012-1-manivannan.sadhasivam@linaro.orgSigned-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
[mkl: mcp251xfd_get_normal_mode(): move CAN_CTRLMODE_LOOPBACK check to front]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/spi/mcp251xfd/mcp251xfd-core.c

@@ -965,7 +965,10 @@ static u8 mcp251xfd_get_normal_mode(const struct mcp251xfd_priv *priv)
 {
 	u8 mode;
 
-	if (priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)
+
+	if (priv->can.ctrlmode & CAN_CTRLMODE_LOOPBACK)
+		mode = MCP251XFD_REG_CON_MODE_INT_LOOPBACK;
+	else if (priv->can.ctrlmode & CAN_CTRLMODE_LISTENONLY)
 		mode = MCP251XFD_REG_CON_MODE_LISTENONLY;
 	else if (priv->can.ctrlmode & CAN_CTRLMODE_FD)
 		mode = MCP251XFD_REG_CON_MODE_MIXED;
@@ -2881,9 +2884,9 @@ static int mcp251xfd_probe(struct spi_device *spi)
 	priv->can.do_get_berr_counter = mcp251xfd_get_berr_counter;
 	priv->can.bittiming_const = &mcp251xfd_bittiming_const;
 	priv->can.data_bittiming_const = &mcp251xfd_data_bittiming_const;
-	priv->can.ctrlmode_supported = CAN_CTRLMODE_LISTENONLY |
-		CAN_CTRLMODE_BERR_REPORTING | CAN_CTRLMODE_FD |
-		CAN_CTRLMODE_FD_NON_ISO;
+	priv->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK |
+		CAN_CTRLMODE_LISTENONLY | CAN_CTRLMODE_BERR_REPORTING |
+		CAN_CTRLMODE_FD | CAN_CTRLMODE_FD_NON_ISO;
 	priv->ndev = ndev;
 	priv->spi = spi;
 	priv->rx_int = rx_int;