USB: serial: handle Data Carrier Detect changes

Alan's commit 335f8514f200e63d689113d29cb7253a5c282967 introduced
.carrier_raised function in several drivers.  That also means
tty_port_block_til_ready can now suspend the process trying to open the serial
port when Carrier Detect is low and put it into tty_port.open_wait queue.  We
need to wake up the process when Carrier Detect goes high and trigger TTY
hangup when CD goes low.

Some of the devices do not report modem status line changes, or at least we
don't understand the status message, so for those we remove .carrier_raised
again.

Signed-off-by: Libor Pechacek <lpechacek@suse.cz>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 20 insertions, 0 deletions

diff --git a/drivers/usb/serial/generic.c b/drivers/usb/serial/generic.c
index e6833e216fc9..e4db5ad2bc55 100644
--- a/drivers/usb/serial/generic.c
+++ b/drivers/usb/serial/generic.c
@@ -479,6 +479,26 @@ int usb_serial_handle_break(struct usb_serial_port *port)
 }
 EXPORT_SYMBOL_GPL(usb_serial_handle_break);
 
+/**
+ *      usb_serial_handle_dcd_change - handle a change of carrier detect state
+ *      @port: usb_serial_port structure for the open port
+ *      @tty: tty_struct structure for the port
+ *      @status: new carrier detect status, nonzero if active
+ */
+void usb_serial_handle_dcd_change(struct usb_serial_port *usb_port,
+                                struct tty_struct *tty, unsigned int status)
+{
+        struct tty_port *port = &usb_port->port;
+
+        dbg("%s - port %d, status %d", __func__, usb_port->number, status);
+
+        if (status)
+                wake_up_interruptible(&port->open_wait);
+        else if (tty && !C_CLOCAL(tty))
+                tty_hangup(tty);
+}
+EXPORT_SYMBOL_GPL(usb_serial_handle_dcd_change);
+
 int usb_serial_generic_resume(struct usb_serial *serial)
 {
         struct usb_serial_port *port;