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>> +     struct uart_8250_port *up = up_to_u8250p(port); >> +     unsigned int xyd_x, nom, denom; >> +     unsigned int baud; >> +     int i; >> + >> +     serial8250_do_set_termios(port, termios, old); >> + >> +     baud = serial8250_get_baud_rate(port, termios, old); >> + >> +     /* Set DLAB to access the baud rate divider registers (BRDH, >> BRDL) */ >> +     serial_port_out(port, UART_LCR, up->lcr | UART_LCR_DLAB); >> + >> +     /* Set baud rate calculation defaults (BRDIV ([BRDH,BRDL]) to 1) */ >> +     serial_port_out(port, UART_AIROHA_BRDL, UART_BRDL_20M); >> +     serial_port_out(port, UART_AIROHA_BRDH, UART_BRDH_20M); >> + >> +     /* >> +      * Calculate XYD_x and XINCLKDR register by searching >> +      * through a table of crystal_clock divisors. >> +      */ >> +     for (i = 0 ; i < ARRAY_SIZE(airoha_clk_div_info) ; i++) { >> +             clk_div_info = &airoha_clk_div_info[i]; >> + >> +             denom = (XINDIV_CLOCK / 40) / clk_div_info->div; >> +             nom = baud * (XYD_Y / 40); > > Are these "/ 40" to avoid overflow? Add a comment. Yes, this is to keep it in 32bits. > >> +             xyd_x = ((nom / denom) << 4); > > * don't you want to round to closest instead of down? > * I don't understand the purpose of the shift though. IIRC this is the vendor calculation logic scaled to fit 32bits. With this rounding/calculation we hit the baud rate exactly for the baud rates that people actually use. > >> +             /* For the HSUART xyd_x needs to be scaled by a factor >> of 2 */ >> +             if (port->type == UART_PORT_AIROHA_HS) >> +                     xyd_x = xyd_x >> 1; > > Do not use shifts for div/mul. > >> +             if (xyd_x < XYD_Y) >> +                     break; >> +     } >> + >> +     serial_port_out(port, UART_AIROHA_XINCLKDR, clk_div_info->mask); >> +     serial_port_out(port, UART_AIROHA_XYD, (xyd_x << 16) | XYD_Y); >> + >> +     /* unset DLAB */ >> +     serial_port_out(port, UART_LCR, up->lcr); >> +} > > thanks, > -- > js > suse labs MvH Benjamin Larsson