From: Ruihong Luo colorsu1922@gmail.com
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@kernel.org Signed-off-by: Ruihong Luo colorsu1922@gmail.com Link: https://lore.kernel.org/stable/20230713004235.35904-1-colorsu1922%40gmail.co... 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 --- 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);