Commit 32262e2e authored by Pali Rohár's avatar Pali Rohár Committed by Greg Kroah-Hartman
Browse files

serial: 8250: Fix reporting real baudrate value in c_ospeed field 



In most cases it is not possible to set exact baudrate value to hardware.

So fix reporting real baudrate value which was set to hardware via c_ospeed
termios field. It can be retrieved by ioctl(TCGETS2) from userspace.

Real baudrate value is calculated from chosen hardware divisor and base
clock. It is implemented in a new function serial8250_compute_baud_rate()
which is inverse of serial8250_get_divisor() function.

With this change is fixed also UART timeout value (it is updated via
uart_update_timeout() function), which is calculated from the now fixed
baudrate value too.

Cc: stable@vger.kernel.org
Signed-off-by: default avatarPali Rohár <pali@kernel.org>
Link: https://lore.kernel.org/r/20210927093704.19768-1-pali@kernel.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 027b5717

drivers/tty/serial/8250/8250_port.c

+17 −0
Original line number Diff line number Diff line
@@ -2584,6 +2584,19 @@ static unsigned int serial8250_get_divisor(struct uart_port *port, 
	return serial8250_do_get_divisor(port, baud, frac);

}



static unsigned int serial8250_compute_baud_rate(struct uart_port *port,

						 unsigned int quot)

{

	if ((port->flags & UPF_MAGIC_MULTIPLIER) && quot == 0x8001)

		return port->uartclk / 4;

	else if ((port->flags & UPF_MAGIC_MULTIPLIER) && quot == 0x8002)

		return port->uartclk / 8;

	else if (port->type == PORT_NPCM)

		return DIV_ROUND_CLOSEST(port->uartclk - 2 * (quot + 2), 16 * (quot + 2));

	else

		return DIV_ROUND_CLOSEST(port->uartclk, 16 * quot);

}



static unsigned char serial8250_compute_lcr(struct uart_8250_port *up,

					    tcflag_t c_cflag)

{
@@ -2714,11 +2727,14 @@ void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) 


	baud = serial8250_get_baud_rate(port, termios, NULL);

	quot = serial8250_get_divisor(port, baud, &frac);

	baud = serial8250_compute_baud_rate(port, quot);



	serial8250_rpm_get(up);

	spin_lock_irqsave(&port->lock, flags);



	uart_update_timeout(port, termios->c_cflag, baud);

	if (tty_termios_baud_rate(termios))

		tty_termios_encode_baud_rate(termios, baud, baud);



	serial8250_set_divisor(port, baud, quot, frac);

	serial_port_out(port, UART_LCR, up->lcr);
@@ -2750,6 +2766,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios, 


	baud = serial8250_get_baud_rate(port, termios, old);

	quot = serial8250_get_divisor(port, baud, &frac);

	baud = serial8250_compute_baud_rate(port, quot);



	/*

	 * Ok, we're now changing the port state.  Do it with