Hi:
My custom board is based on allwinner R40, the uart is compatibled with
serial8250. Based on it's datasheet:
> When TX transmit data, or RX receives data, or TX FIFO is not empty,
then the
> BUSY flag bit can be set to 1 by hardware, which indicates the UART
> controller is busy.
We cannot write LCR and DLL to update UART params such as baudrate and
partity
while the UART is busy, however `serial8250_do_set_termios` is a void
function,
the upper level always assume the uart params is updated.
The upper level `uart_set_termios` do noting if ktermios params is not
changed,
it will not update when the user space program running tcsetattr set a same
baudrate again. So we can not fix the baudrate when
`serial8250_do_set_termios`
failed.
Allwinner R40's datasheet provided a way for this case.
> CHCFG_AT_BUSY(configure at busy): Enable the bit, software can also
set UART
> controller when UART is busy, such as the LCR, DLH, DLL register.
> CHANGE_UPDATE(change update): If CHCFG_AT_BUSY is enabled, and
CHANGE_UPDATE
> is written to 1, the configuration of UART controller can be updated.
> After completed update, the bit is cleared to 0 automatically.
I can't know this feature is expanded by allwinner, or it is a common
functiton
of serial8250. Perhaps the serial8250 driver need this.
Thanks
