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: 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>
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