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serial: 8250: Preserve DLD[7:4] for PORT_XR17V35X 

The upper four bits of the XR17V35x fractional divisor register (DLD)
control general chip function (RS-485 direction pin polarity, multidrop
mode, XON/XOFF parity check, and fast IR mode). Don't allow these bits
to be clobbered when setting the baudrate.

Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Aaron Sierra 2017-10-04 10:01:28 -05:00 committed by Greg Kroah-Hartman
parent 8ffb82094b
commit 0ab84da2e0
1 changed files with 4 additions and 1 deletions
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5
drivers/tty/serial/8250/8250_port.c
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@ -2586,8 +2586,11 @@ static void serial8250_set_divisor(struct uart_port *port, unsigned int baud,
serial_dl_write(up, quot);
/* XR17V35x UARTs have an extra fractional divisor register (DLD) */
if (up->port.type == PORT_XR17V35X)
if (up->port.type == PORT_XR17V35X) {
/* Preserve bits not related to baudrate; DLD[7:4]. */
quot_frac |= serial_port_in(port, 0x2) & 0xf0;
serial_port_out(port, 0x2, quot_frac);
}
}
static unsigned int serial8250_get_baud_rate(struct uart_port *port,