On Thu, Jul 02, 2020 at 06:11:52AM +0200, Lukas Wunner wrote: > On Thu, Jul 02, 2020 at 01:37:13AM +0300, Serge Semin wrote: > > 1) Add a new capability like UART_CAP_NO16DIV and take it into account > > in the serial8250_get_baud_rate() method. > > > > I don't have a documentation for the Mediatek UART port, but it seems to me > > that that controller calculates the baud rate differently from the standard > > 8250 port. A standard 8250 port does that by the next formulae: > > baud = uartclk / (16 * divisor). > > While it seems to me that the Mediatek port uses the formulae like: > > baud = uartclk / divisor. (Please, correct me if I'm wrong) > > 8250_bcm2835aux.c seems to suffer from a similar issue and > solves it like this in the ->probe hook: > > /* the HW-clock divider for bcm2835aux is 8, > * but 8250 expects a divider of 16, > * so we have to multiply the actual clock by 2 > * to get identical baudrates. > */ > up.port.uartclk = clk_get_rate(data->clk) * 2; 8250_mid for example lies about UART clock due to this. It has a comment in the code in its ->set_termios(). Yes, we have a lot of possibilities here to fix, I guess. We have custom termios callback, also get and set divisor and so on. -- With Best Regards, Andy Shevchenko
