linux-kernel - [PATCH 5.4 69/71] serial: stm32: Clear prev values before setting RTS delays

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Message-Id: <20220719114559.346970211@linuxfoundation.org>
Date:   Tue, 19 Jul 2022 13:54:32 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, stable <stable@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: [PATCH 5.4 69/71] serial: stm32: Clear prev values before setting RTS delays

From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

commit 5c5f44e36217de5ead789ff25da71c31c2331c96 upstream.

The code lacks clearing of previous DEAT/DEDT values. Thus, changing
values on the fly results in garbage delays tending towards the maximum
value as more and more bits are ORed together. (Leaving RS485 mode
would have cleared the old values though).

Fixes: 1bcda09d2910 ("serial: stm32: add support for RS485 hardware control mode")
Cc: stable <stable@...nel.org>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Link: https://lore.kernel.org/r/20220627150753.34510-1-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/tty/serial/stm32-usart.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -73,6 +73,8 @@ static void stm32_config_reg_rs485(u32 *
 	*cr3 |= USART_CR3_DEM;
 	over8 = *cr1 & USART_CR1_OVER8;
 
+	*cr1 &= ~(USART_CR1_DEDT_MASK | USART_CR1_DEAT_MASK);
+
 	if (over8)
 		rs485_deat_dedt = delay_ADE * baud * 8;
 	else