can: rockchip_canfd: add support for CAN_CTRLMODE_LOOPBACK

Add support for loopback mode.
Tested-by: Alibek Omarov <a1ba.omarov@gmail.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patch.msgid.link/20240904-rockchip-canfd-v5-19-8ae22bcb27cc@pengutronix.deSigned-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/rockchip/rockchip_canfd-core.c

@@ -276,6 +276,11 @@ static void rkcanfd_chip_start(struct rkcanfd_priv *priv)
 		RKCANFD_REG_MODE_RXSTX_MODE |
 		RKCANFD_REG_MODE_WORK_MODE;
 
+	if (priv->can.ctrlmode & CAN_CTRLMODE_LOOPBACK)
+		priv->reg_mode_default |= RKCANFD_REG_MODE_LBACK_MODE |
+			RKCANFD_REG_MODE_SILENT_MODE |
+			RKCANFD_REG_MODE_SELF_TEST;
+
 	/* mask, i.e. ignore:
 	 * - TIMESTAMP_COUNTER_OVERFLOW_INT - timestamp counter overflow interrupt
 	 * - TX_ARBIT_FAIL_INT - TX arbitration fail interrupt
@@ -894,7 +899,7 @@ static int rkcanfd_probe(struct platform_device *pdev)
 	priv->can.clock.freq = clk_get_rate(priv->clks[0].clk);
 	priv->can.bittiming_const = &rkcanfd_bittiming_const;
 	priv->can.data_bittiming_const = &rkcanfd_data_bittiming_const;
-	priv->can.ctrlmode_supported = 0;
+	priv->can.ctrlmode_supported = CAN_CTRLMODE_LOOPBACK;
 	if (!(priv->devtype_data.quirks & RKCANFD_QUIRK_CANFD_BROKEN))
 		priv->can.ctrlmode_supported |= CAN_CTRLMODE_FD;
 	priv->can.do_set_mode = rkcanfd_set_mode;

drivers/net/can/rockchip/rockchip_canfd-rx.c

@@ -243,7 +243,7 @@ static int rkcanfd_handle_rx_int_one(struct rkcanfd_priv *priv)
 		err = rkcanfd_rxstx_filter(priv, cfd, header->ts, &tx_done);
 		if (err)
 			return err;
-		if (tx_done)
+		if (tx_done && !(priv->can.ctrlmode & CAN_CTRLMODE_LOOPBACK))
 			return 0;
 	}