linux-kernel - [PATCH] tty: serial: Work around warning backtrace in serial8250_set

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Message-ID: <20241205143033.2695333-1-linux@roeck-us.net>
Date: Thu,  5 Dec 2024 06:30:33 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Jiri Slaby <jirislaby@...nel.org>,
	linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org,
	Guenter Roeck <linux@...ck-us.net>,
	Arnd Bergmann <arnd@...db.de>,
	Niklas Schnelle <schnelle@...ux.ibm.com>
Subject: [PATCH] tty: serial: Work around warning backtrace in serial8250_set_defaults

Commit 7c7e6c8924e7 ("tty: serial: handle HAS_IOPORT dependencies")
triggers warning backtraces on a number of platforms which don't support
IO ports.

WARNING: CPU: 0 PID: 0 at drivers/tty/serial/8250/8250_port.c:470 serial8250_set_defaults+0x148/0x1d8
Unsupported UART type 0

The problem is seen because serial8250_set_defaults() is called for
all members of the serial8250_ports[] array even if that array is
not initialized.

Work around the problem by only displaying the warning if the port
type is not 0 (UPIO_PORT) or if iobase is set for the port.

Fixes: 7c7e6c8924e7 ("tty: serial: handle HAS_IOPORT dependencies")
Acked-by: Arnd Bergmann <arnd@...db.de>
Cc: Niklas Schnelle <schnelle@...ux.ibm.com>
Signed-off-by: Guenter Roeck <linux@...ck-us.net>
---
A complete fix will require a sequence of patches, which will have to be
tested thoroughly and is thus not 6.13 material. This patch doesn't fix
the underlying problem, but it is good enough for 6.13, or at least not
worse than 6.12, while at the same time avoiding the warning backtrace.

 drivers/tty/serial/8250/8250_port.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 4d63d80e78a9..649e74e9b52f 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -467,7 +467,8 @@ static void set_io_from_upio(struct uart_port *p)
 		break;
 #endif
 	default:
-		WARN(1, "Unsupported UART type %x\n", p->iotype);
+		WARN(p->iotype != UPIO_PORT || p->iobase,
+		     "Unsupported UART type %x\n", p->iotype);
 		p->serial_in = no_serial_in;
 		p->serial_out = no_serial_out;
 	}
-- 
2.45.2