USB: serial: xr: fix B0 handling

Fix up B0 handling which should leave the baud rate unchanged and
specifically not report back a non-B0 rate when B0 is requested; must
temporarily disable hardware flow control so that RTS can be deasserted;
and should reassert DTR/RTS when moving from B0.

Fixes: c2d405aa86b4 ("USB: serial: add MaxLinear/Exar USB to Serial driver")
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/xr_serial.c b/drivers/usb/serial/xr_serial.c
index f67e7db..483d07d 100644 (file)
--- a/drivers/usb/serial/xr_serial.c
+++ b/drivers/usb/serial/xr_serial.c
@@ -341,8 +341,11 @@ static int xr_set_baudrate(struct tty_struct *tty,
        u16 tx_mask, rx_mask;
        int ret;
 
-       baud = clamp(tty->termios.c_ospeed, XR21V141X_MIN_SPEED,
-                    XR21V141X_MAX_SPEED);
+       baud = tty->termios.c_ospeed;
+       if (!baud)
+               return 0;
+
+       baud = clamp(baud, XR21V141X_MIN_SPEED, XR21V141X_MAX_SPEED);
        divisor = XR_INT_OSC_HZ / baud;
        idx = ((32 * XR_INT_OSC_HZ) / baud) & 0x1f;
        tx_mask = xr21v141x_txrx_clk_masks[idx].tx;
@@ -399,7 +402,8 @@ static int xr_set_baudrate(struct tty_struct *tty,
 }
 
 static void xr_set_flow_mode(struct tty_struct *tty,
-                            struct usb_serial_port *port)
+                            struct usb_serial_port *port,
+                            struct ktermios *old_termios)
 {
        u8 flow, gpio_mode;
        int ret;
@@ -411,7 +415,7 @@ static void xr_set_flow_mode(struct tty_struct *tty,
        /* Set GPIO mode for controlling the pins manually by default. */
        gpio_mode &= ~XR21V141X_UART_MODE_GPIO_MASK;
 
-       if (C_CRTSCTS(tty)) {
+       if (C_CRTSCTS(tty) && C_BAUD(tty) != B0) {
                dev_dbg(&port->dev, "Enabling hardware flow ctrl\n");
                gpio_mode |= XR21V141X_UART_MODE_RTS_CTS;
                flow = XR21V141X_UART_FLOW_MODE_HW;
@@ -438,6 +442,11 @@ static void xr_set_flow_mode(struct tty_struct *tty,
        xr_uart_enable(port);
 
        xr_set_reg_uart(port, XR21V141X_REG_GPIO_MODE, gpio_mode);
+
+       if (C_BAUD(tty) == B0)
+               xr_dtr_rts(port, 0);
+       else if (old_termios && (old_termios->c_cflag & CBAUD) == B0)
+               xr_dtr_rts(port, 1);
 }
 
 static void xr_set_termios(struct tty_struct *tty,
@@ -493,11 +502,7 @@ static void xr_set_termios(struct tty_struct *tty,
        if (ret)
                return;
 
-       /* If baud rate is B0, clear DTR and RTS */
-       if (C_BAUD(tty) == B0)
-               xr_dtr_rts(port, 0);
-
-       xr_set_flow_mode(tty, port);
+       xr_set_flow_mode(tty, port, old_termios);
 }
 
 static int xr_open(struct tty_struct *tty, struct usb_serial_port *port)