serial: mtk: rewrite the setbrg function
Currently the setbrg logic of serial-mtk is messy, and should be rewritten.
Also an option is added to make it possible to use highspeed-3 mode for all
bauds.
The new logic is:
1. If baud clock > 12MHz
a) If baud <= 115200, highspeed-0 mode will be used (ns16550 compatible)
b) If baud <= 576000, highspeed-2 mode will be used
c) any bauds > 576000, highspeed-3 mode will be used
2. If baud clock <= 12MHz
Forced highspeed-3 mode
a) If baud <= 115200, calculates the divisor using DIV_ROUND_CLOSEST
b) any bauds > 115200, the same as 1. c)
1 file changed