From 45a7bd635930baa960b6817674c64bdfb8f39570 Mon Sep 17 00:00:00 2001 From: Joe Schultz Date: Tue, 11 Feb 2014 18:30:01 -0600 Subject: [PATCH] serial: 8250: Support XR17V35x fraction divisor The Exar XR17V35x family of UARTs have an additional fractional divisor register (DLD) which was not being used. Calculate and set this register for these devices to reduce their baud rate error. Signed-off-by: Joe Schultz Signed-off-by: Aaron Sierra Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_core.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c index 61ecd709a722..69932b7556cf 100644 --- a/drivers/tty/serial/8250/8250_core.c +++ b/drivers/tty/serial/8250/8250_core.c @@ -2432,6 +2432,24 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios, serial_dl_write(up, quot); + /* + * XR17V35x UARTs have an extra fractional divisor register (DLD) + * + * We need to recalculate all of the registers, because DLM and DLL + * are already rounded to a whole integer. + * + * When recalculating we use a 32x clock instead of a 16x clock to + * allow 1-bit for rounding in the fractional part. + */ + if (up->port.type == PORT_XR17V35X) { + unsigned int baud_x32 = (port->uartclk * 2) / baud; + u16 quot = baud_x32 / 32; + u8 quot_frac = DIV_ROUND_CLOSEST(baud_x32 % 32, 2); + + serial_dl_write(up, quot); + serial_port_out(port, 0x2, quot_frac & 0xf); + } + /* * LCR DLAB must be set to enable 64-byte FIFO mode. If the FCR * is written without DLAB set, this mode will be disabled. -- 2.20.1