can: rcar_can: rcar_can_resume(): fix s2ram with PSCI

On R-Car Gen3 using PSCI, s2ram powers down the SoC.  After resume, the
CAN interface no longer works, until it is brought down and up again.

Fix this by calling rcar_can_start() from the PM resume callback, to
fully initialize the controller instead of just restarting it.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/699b2f7fcb60b31b6f976a37f08ce99c5ffccb31.1755165227.git.geert+renesas@glider.be
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

Author: geertu

drivers/net/can/rcar/rcar_can.c

@@ -861,7 +861,6 @@ static int rcar_can_resume(struct device *dev)
 {
 	struct net_device *ndev = dev_get_drvdata(dev);
 	struct rcar_can_priv *priv = netdev_priv(ndev);
-	u16 ctlr;
 	int err;
 
 	if (!netif_running(ndev))
@@ -873,12 +872,7 @@ static int rcar_can_resume(struct device *dev)
 		return err;
 	}
 
-	ctlr = readw(&priv->regs->ctlr);
-	ctlr &= ~RCAR_CAN_CTLR_SLPM;
-	writew(ctlr, &priv->regs->ctlr);
-	ctlr &= ~RCAR_CAN_CTLR_CANM;
-	writew(ctlr, &priv->regs->ctlr);
-	priv->can.state = CAN_STATE_ERROR_ACTIVE;
+	rcar_can_start(ndev);
 
 	netif_device_attach(ndev);
 	netif_start_queue(ndev);