linux-kernel - [PATCH v4 4/5] serial: 8250: Also set sticky MCR bits in console restoration

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Date:   Mon, 18 Apr 2022 00:02:41 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH v4 4/5] serial: 8250: Also set sticky MCR bits in console
 restoration

Sticky MCR bits are lost in console restoration if console suspending 
has been disabled.  This currently affects the AFE bit, which works in 
combination with RTS which we set, so we want to make sure the UART 
retains control of its FIFO where previously requested.  Also specific 
drivers may need other bits in the future.

Signed-off-by: Maciej W. Rozycki <macro@...am.me.uk>
Fixes: 4516d50aabed ("serial: 8250: Use canary to restart console after suspend")
Cc: stable@...r.kernel.org # v4.0+
---
New change in v4, factored out from 5/5.
---
 drivers/tty/serial/8250/8250_port.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

linux-serial-8250-mcr-restore.diff
Index: linux-macro/drivers/tty/serial/8250/8250_port.c
===================================================================
--- linux-macro.orig/drivers/tty/serial/8250/8250_port.c
+++ linux-macro/drivers/tty/serial/8250/8250_port.c
@@ -3308,7 +3308,7 @@ static void serial8250_console_restore(s
 
 	serial8250_set_divisor(port, baud, quot, frac);
 	serial_port_out(port, UART_LCR, up->lcr);
-	serial8250_out_MCR(up, UART_MCR_DTR | UART_MCR_RTS);
+	serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS);
 }
 
 /*