USB: cdc-acm: only raise DTR on transitions from B0

Make sure to only raise DTR on transitions from B0 in set_termios.

Also allow set_termios to be called from open with a termios_old of
NULL. Note that DTR will not be raised prematurely in this case.

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 3 insertions, 2 deletions

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 6771f884cb82..9d6495424b06 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -985,11 +985,12 @@ static void acm_tty_set_termios(struct tty_struct *tty,
         /* FIXME: Needs to clear unsupported bits in the termios */
         acm->clocal = ((termios->c_cflag & CLOCAL) != 0);
 
-        if (!newline.dwDTERate) {
+        if (C_BAUD(tty) == B0) {
                 newline.dwDTERate = acm->line.dwDTERate;
                 newctrl &= ~ACM_CTRL_DTR;
-        } else
+        } else if (termios_old && (termios_old->c_cflag & CBAUD) == B0) {
                 newctrl |=  ACM_CTRL_DTR;
+        }
 
         if (newctrl != acm->ctrlout)
                 acm_set_control(acm, acm->ctrlout = newctrl);