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:
- 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.