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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 <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>
This commit is contained in:
Ruihong Luo 2023-07-13 08:42:36 +08:00 committed by Greg Kroah-Hartman
parent 016a4a2a75
commit ace0efeb56
1 changed files with 4 additions and 2 deletions
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6
drivers/tty/serial/8250/8250_dwlib.c
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@ -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);