linux-kernel - [PATCH v4 2/5] serial/8250: Use the cache value of the FCR register

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Message-Id: <20220316143646.13301-3-wander@redhat.com>
Date:   Wed, 16 Mar 2022 11:36:41 -0300
From:   Wander Lairson Costa <wander@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Johan Hovold <johan@...nel.org>,
        Wander Lairson Costa <wander@...hat.com>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Serge Semin <fancer.lancer@...il.com>,
        Lukas Wunner <lukas@...ner.de>,
        Pali Rohár <pali@...nel.org>,
        linux-serial@...r.kernel.org (open list:SERIAL DRIVERS),
        linux-kernel@...r.kernel.org (open list)
Cc:     rostedt@...dmis.org, senozhatsky@...omium.org,
        andre.goddard@...il.com, sudipm.mukherjee@...il.com,
        andy.shevchenko@...il.com, David.Laight@...lab.com,
        jonathanh@...dia.com, phil@...pberrypi.com
Subject: [PATCH v4 2/5] serial/8250: Use the cache value of the FCR register

commit 5021d709b31b ("tty: serial: Use fifo in 8250 console driver")
erroneous tries to read the FCR register content, but this register is
write-only.

This patch fixes that by reading the content from the port struct fcr
field.

Thanks to Jon Hunter and Jiri Slaby.

Suggested-by: Jiri Slaby <jirislaby@...nel.org>
Reported-by: Jon Hunter <jonathanh@...dia.com>
Signed-off-by: Wander Lairson Costa <wander@...hat.com>
---
 drivers/tty/serial/8250/8250_port.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 2abb3de11a48..9f3fa9fe2a4e 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -3410,7 +3410,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 
 	use_fifo = (up->capabilities & UART_CAP_FIFO) &&
 		port->fifosize > 1 &&
-		(serial_port_in(port, UART_FCR) & UART_FCR_ENABLE_FIFO) &&
+		(up->fcr & UART_FCR_ENABLE_FIFO) &&
 		/*
 		 * After we put a data in the fifo, the controller will send
 		 * it regardless of the CTS state. Therefore, only use fifo
-- 
2.35.1