From: Pali Rohár pali@kernel.org
commit 32262e2e429cdb31f9e957e997d53458762931b7 upstream.
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: Pali Rohár pali@kernel.org Link: https://lore.kernel.org/r/20210927093704.19768-1-pali@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/tty/serial/8250/8250_port.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+)
--- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2584,6 +2584,19 @@ static unsigned int serial8250_get_divis 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) { @@ -2725,11 +2738,14 @@ void serial8250_update_uartclk(struct ua
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); @@ -2763,6 +2779,7 @@ serial8250_do_set_termios(struct uart_po
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