From 748c5ea8b8796ae8ee80b8d3a3d940570b588d59 Mon Sep 17 00:00:00 2001 From: Ruihong Luo Date: Thu, 13 Jul 2023 08:42:36 +0800 Subject: [PATCH] serial: 8250_dw: Preserve original value of DLF register MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit Preserve the original value of the Divisor Latch Fraction (DLF) register. When the DLF register is modified without preservation, it can disrupt the baudrate settings established by firmware or bootloader, leading to data corruption and the generation of unreadable or distorted characters. Fixes: 701c5e73b296 ("serial: 8250_dw: add fractional divisor support") Cc: stable Signed-off-by: Ruihong Luo Link: https://lore.kernel.org/stable/20230713004235.35904-1-colorsu1922%40gmail.com Reviewed-by: Ilpo Järvinen Reviewed-by: Andy Shevchenko Link: https://lore.kernel.org/r/20230713004235.35904-1-colorsu1922@gmail.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_dwlib.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_dwlib.c b/drivers/tty/serial/8250/8250_dwlib.c index 75f32f054ebb1..84843e204a5e8 100644 --- a/drivers/tty/serial/8250/8250_dwlib.c +++ b/drivers/tty/serial/8250/8250_dwlib.c @@ -244,7 +244,7 @@ void dw8250_setup_port(struct uart_port *p) struct dw8250_port_data *pd = p->private_data; struct dw8250_data *data = to_dw8250_data(pd); struct uart_8250_port *up = up_to_u8250p(p); - u32 reg; + u32 reg, old_dlf; pd->hw_rs485_support = dw8250_detect_rs485_hw(p); if (pd->hw_rs485_support) { @@ -270,9 +270,11 @@ void dw8250_setup_port(struct uart_port *p) dev_dbg(p->dev, "Designware UART version %c.%c%c\n", (reg >> 24) & 0xff, (reg >> 16) & 0xff, (reg >> 8) & 0xff); + /* Preserve value written by firmware or bootloader */ + old_dlf = dw8250_readl_ext(p, DW_UART_DLF); dw8250_writel_ext(p, DW_UART_DLF, ~0U); reg = dw8250_readl_ext(p, DW_UART_DLF); - dw8250_writel_ext(p, DW_UART_DLF, 0); + dw8250_writel_ext(p, DW_UART_DLF, old_dlf); if (reg) { pd->dlf_size = fls(reg); -- 2.30.2