This is a note to let you know that I've just added the patch titled
serial: 8250_dw: Preserve original value of DLF register
to the 6.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
serial-8250_dw-preserve-original-value-of-dlf-register.patch
and it can be found in the queue-6.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 748c5ea8b8796ae8ee80b8d3a3d940570b588d59 Mon Sep 17 00:00:00 2001
From: Ruihong Luo <colorsu1922@xxxxxxxxx>
Date: Thu, 13 Jul 2023 08:42:36 +0800
Subject: serial: 8250_dw: Preserve original value of DLF register
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From: Ruihong Luo <colorsu1922@xxxxxxxxx>
commit 748c5ea8b8796ae8ee80b8d3a3d940570b588d59 upstream.
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 <stable@xxxxxxxxxx>
Signed-off-by: Ruihong Luo <colorsu1922@xxxxxxxxx>
Link: https://lore.kernel.org/stable/20230713004235.35904-1-colorsu1922%40gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230713004235.35904-1-colorsu1922@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/8250/8250_dwlib.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
--- 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
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
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);
Patches currently in stable-queue which might be from colorsu1922@xxxxxxxxx are
queue-6.4/serial-8250_dw-preserve-original-value-of-dlf-register.patch
