serial: sh-sci: Do not probe the serial port if its slot in sci_ports[] is in use

In the sh-sci driver, sci_ports[0] is used by earlycon. If the earlycon is
still active when sci_probe() is called and the new serial port is supposed
to map to sci_ports[0], return -EBUSY to prevent breaking the earlycon.

This situation should occurs in debug scenarios, and users should be
aware of the potential conflict.

Fixes: 0b0cced ("serial: sh-sci: Add CONFIG_SERIAL_EARLYCON support")
Cc: [email protected]
Signed-off-by: Claudiu Beznea <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: claudiubeznea

drivers/tty/serial/sh-sci.c

@@ -165,6 +165,7 @@ struct sci_port {
 static struct sci_port sci_ports[SCI_NPORTS];
 static unsigned long sci_ports_in_use;
 static struct uart_driver sci_uart_driver;
+static bool sci_uart_earlycon;
 
 static inline struct sci_port *
 to_sci_port(struct uart_port *uart)
@@ -3438,6 +3439,7 @@ static int sci_probe_single(struct platform_device *dev,
 static int sci_probe(struct platform_device *dev)
 {
 	struct plat_sci_port *p;
+	struct resource *res;
 	struct sci_port *sp;
 	unsigned int dev_id;
 	int ret;
@@ -3467,6 +3469,26 @@ static int sci_probe(struct platform_device *dev)
 	}
 
 	sp = &sci_ports[dev_id];
+
+	/*
+	 * In case:
+	 * - the probed port alias is zero (as the one used by earlycon), and
+	 * - the earlycon is still active (e.g., "earlycon keep_bootcon" in
+	 *   bootargs)
+	 *
+	 * defer the probe of this serial. This is a debug scenario and the user
+	 * must be aware of it.
+	 *
+	 * Except when the probed port is the same as the earlycon port.
+	 */
+
+	res = platform_get_resource(dev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -ENODEV;
+
+	if (sci_uart_earlycon && sp == &sci_ports[0] && sp->port.mapbase != res->start)
+		return dev_err_probe(&dev->dev, -EBUSY, "sci_port[0] is used by earlycon!\n");
+
 	platform_set_drvdata(dev, sp);
 
 	ret = sci_probe_single(dev, dev_id, p, sp);
@@ -3563,6 +3585,7 @@ static int __init early_console_setup(struct earlycon_device *device,
 	port_cfg.type = type;
 	sci_ports[0].cfg = &port_cfg;
 	sci_ports[0].params = sci_probe_regmap(&port_cfg);
+	sci_uart_earlycon = true;
 	port_cfg.scscr = sci_serial_in(&sci_ports[0].port, SCSCR);
 	sci_serial_out(&sci_ports[0].port, SCSCR,
 		       SCSCR_RE | SCSCR_TE | port_cfg.scscr);