From: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> stable inclusion from stable-v5.10.132 commit b8c4661126568b8cd3e18908b920c3f83eba28e1 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I5YS3T Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- 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@kernel.org> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> Link: https://lore.kernel.org/r/20220627150753.34510-1-ilpo.jarvinen@linux.intel.c... Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com> Acked-by: Xie XiuQi <xiexiuqi@huawei.com> --- drivers/tty/serial/stm32-usart.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c index 8cd9e5b077b6..9377da1e97c0 100644 --- a/drivers/tty/serial/stm32-usart.c +++ b/drivers/tty/serial/stm32-usart.c @@ -70,6 +70,8 @@ static void stm32_usart_config_reg_rs485(u32 *cr1, u32 *cr3, u32 delay_ADE, *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 -- 2.20.1