linux-kernel - [PATCH RFT 4/6] serial: sh-sci: Do not probe the serial port if its slot in sci

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Message-Id: <20241204155806.3781200-5-claudiu.beznea.uj@bp.renesas.com>
Date: Wed,  4 Dec 2024 17:58:04 +0200
From: Claudiu <claudiu.beznea@...on.dev>
To: gregkh@...uxfoundation.org,
	jirislaby@...nel.org,
	wsa+renesas@...g-engineering.com,
	geert+renesas@...der.be,
	prabhakar.mahadev-lad.rj@...renesas.com,
	lethal@...ux-sh.org,
	g.liakhovetski@....de,
	groeck@...omium.org,
	mka@...omium.org,
	ulrich.hecht+renesas@...il.com,
	ysato@...rs.sourceforge.jp
Cc: claudiu.beznea@...on.dev,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	linux-renesas-soc@...r.kernel.org,
	Claudiu Beznea <claudiu.beznea.uj@...renesas.com>,
	stable@...r.kernel.org
Subject: [PATCH RFT 4/6] serial: sh-sci: Do not probe the serial port if its slot in sci_ports[] is in use

From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>

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: 0b0cced19ab1 ("serial: sh-sci: Add CONFIG_SERIAL_EARLYCON support")
Cc: stable@...r.kernel.org
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
---
 drivers/tty/serial/sh-sci.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 373195995d3b..e12fbc71082a 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -158,6 +158,7 @@ struct sci_port {
 	bool has_rtscts;
 	bool autorts;
 	bool tx_occurred;
+	bool earlycon;
 };
 
 #define SCI_NPORTS CONFIG_SERIAL_SH_SCI_NR_UARTS
@@ -3443,6 +3444,7 @@ 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;
@@ -3472,6 +3474,26 @@ 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 (sp->earlycon && res->start != sp->port.mapbase)
+		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);
@@ -3568,6 +3590,7 @@ 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_ports[0].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);
-- 
2.39.2