FAILED: patch "[PATCH] serial: 8250_dw: Preserve original value of DLF register" failed to apply to 4.19-stable tree

FAILED: patch "[PATCH] serial: 8250_dw: Preserve original value of DLF register" failed to apply to 4.19-stable tree

[gregkh]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x 748c5ea8b8796ae8ee80b8d3a3d940570b588d59
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2023073141-suspend-gloss-a42a@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

748c5ea8b879 ("serial: 8250_dw: Preserve original value of DLF register")
136e0ab99b22 ("serial: 8250_dw: split Synopsys DesignWare 8250 common functions")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 748c5ea8b8796ae8ee80b8d3a3d940570b588d59 Mon Sep 17 00:00:00 2001
From: Ruihong Luo <colorsu1922@gmail.com>
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=UTF-8
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 <stable@kernel.org>
Signed-off-by: Ruihong Luo <colorsu1922@gmail.com>
Link: https://lore.kernel.org/stable/20230713004235.35904-1-colorsu1922%40gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230713004235.35904-1-colorsu1922@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_dwlib.c b/drivers/tty/serial/8250/8250_dwlib.c
index 75f32f054ebb..84843e204a5e 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);