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serial: 8250_dw: Preserve original value of DLF register

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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: 701c5e73b2 ("serial: 8250_dw: add fractional divisor support")
Cc: stable <[email protected]>
Signed-off-by: Ruihong Luo <[email protected]>
Link: https://lore.kernel.org/stable/20230713004235.35904-1-colorsu1922%40gmail.com
Reviewed-by: Ilpo Järvinen <[email protected]>
Reviewed-by: Andy Shevchenko <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>
This commit is contained in:
Ruihong Luo 2023-07-13 08:42:36 +08:00 • committed by Greg Kroah-Hartman
commit d674cb90a9
1 changed files with 4 additions and 2 deletions
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6
drivers/tty/serial/8250/8250_dwlib.c
View file

@ -80,7 +80,7 @@ static void dw8250_set_divisor(struct uart_port *p, unsigned int baud,
void dw8250_setup_port(struct uart_port *p)
{
struct uart_8250_port *up = up_to_u8250p(p);
u32 reg;
u32 reg, old_dlf;
/*
* If the Component Version Register returns zero, we know that
@ -93,9 +93,11 @@ 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) {
struct dw8250_port_data *d = p->private_data;