linux-kernel - [PATCH v2 1/5] serial: core: tidy invalid baudrate handling in uart_get_baud

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Date:   Tue, 19 Sep 2023 19:26:40 -0700
From:   Max Filippov <jcmvbkbc@...il.com>
To:     linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        devicetree@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Max Filippov <jcmvbkbc@...il.com>
Subject: [PATCH v2 1/5] serial: core: tidy invalid baudrate handling in uart_get_baud_rate

uart_get_baud_rate has input parameters 'min' and 'max' limiting the
range of acceptable baud rates from the caller's perspective. If neither
current or old termios structures have acceptable baud rate setting and
9600 is not in the min/max range either the function returns 0 and
issues a warning.
However for a UART that does not support speed of 9600 baud this is
expected behavior.
Clarify that 0 can be (and always could be) returned from the
uart_get_baud_rate. Don't issue a warning in that case.
Move the warinng to the uart_get_divisor instead, which is often called
with the uart_get_baud_rate return value.

Signed-off-by: Max Filippov <jcmvbkbc@...il.com>
---
 drivers/tty/serial/serial_core.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 7bdc21d5e13b..a8e2915832e8 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -431,7 +431,7 @@ EXPORT_SYMBOL(uart_update_timeout);
  * baud.
  *
  * If the new baud rate is invalid, try the @old termios setting. If it's still
- * invalid, we try 9600 baud.
+ * invalid, we try 9600 baud. If that is also invalid 0 is returned.
  *
  * The @termios structure is updated to reflect the baud rate we're actually
  * going to be using. Don't do this for the case where B0 is requested ("hang
@@ -515,8 +515,6 @@ uart_get_baud_rate(struct uart_port *port, struct ktermios *termios,
 							max - 1, max - 1);
 		}
 	}
-	/* Should never happen */
-	WARN_ON(1);
 	return 0;
 }
 EXPORT_SYMBOL(uart_get_baud_rate);
@@ -539,6 +537,7 @@ uart_get_divisor(struct uart_port *port, unsigned int baud)
 {
 	unsigned int quot;
 
+	WARN_ON(baud == 0);
 	/*
 	 * Old custom speed handling.
 	 */
-- 
2.30.2