Commit 748c5ea8 authored by Ruihong Luo's avatar Ruihong Luo Committed by Greg Kroah-Hartman
Browse files

serial: 8250_dw: Preserve original value of DLF register 



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: 701c5e73 ("serial: 8250_dw: add fractional divisor support")
Cc: stable <stable@kernel.org>
Signed-off-by: default avatarRuihong Luo <colorsu1922@gmail.com>
Link: https://lore.kernel.org/stable/20230713004235.35904-1-colorsu1922%40gmail.com


Reviewed-by: default avatarIlpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230713004235.35904-1-colorsu1922@gmail.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 57c984f6

drivers/tty/serial/8250/8250_dwlib.c

+4 −2
Original line number Diff line number Diff line
@@ -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);