linux-kernel - [PATCH -next] serial: pl011: set UART011_CR_RXE in pl011_set

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Message-Id: <20230501070909.1144547-1-xiehongyu1@kylinos.cn>
Date:   Mon,  1 May 2023 15:09:09 +0800
From:   Hongyu Xie <xiehongyu1@...inos.cn>
To:     linux@...linux.org.uk, gregkh@...uxfoundation.org,
        jirislaby@...nel.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Hongyu Xie <xiehongyu1@...inos.cn>
Subject: [PATCH -next] serial: pl011: set UART011_CR_RXE in pl011_set_termios after port shutdown

UART011_CR_RXE is set in pl011_startup() during normal initialization, and
cleared by pl011_disable_uart() during port shutdown.

You can use a none-console port in poll mode like kgdboc does with
tty_find_polling_driver() after a port shutdown. But pl011_startup() is not
called in tty_find_polling_driver(). So you need to set UART011_CR_RXE to
reenable receive function.

Not sure setting UART011_CR_RXE in pl011_set_termios() is a good idea
through.

Signed-off-by: Hongyu Xie <xiehongyu1@...inos.cn>
---
 drivers/tty/serial/amba-pl011.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index d8c2f3455eeb..c5c3f4674459 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2166,6 +2166,13 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
 	 * ----------^----------^----------^----------^-----
 	 */
 	pl011_write_lcr_h(uap, lcr_h);
+
+	/*
+	 * Receive was disabled by pl011_disable_uart during shutdown.
+	 * Need to reenable receive if you need to use a tty_driver
+	 * returns from tty_find_polling_driver() after a port shutdown.
+	 */
+	old_cr |= UART011_CR_RXE;
 	pl011_write(old_cr, uap, REG_CR);
 
 	spin_unlock_irqrestore(&port->lock, flags);
-- 
2.34.1