USB: serial: handle Data Carrier Detect changes

Alan's commit 335f8514f2 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>

drivers/usb/serial/spcp8x5.c

@@ -133,7 +133,7 @@ struct spcp8x5_usb_ctrl_arg {
 
 /* how come ??? */
 #define UART_STATE			0x08
-#define UART_STATE_TRANSIENT_MASK	0x74
+#define UART_STATE_TRANSIENT_MASK	0x75
 #define UART_DCD			0x01
 #define UART_DSR			0x02
 #define UART_BREAK_ERROR		0x04
@@ -525,6 +525,10 @@ static void spcp8x5_process_read_urb(struct urb *urb)
 		/* overrun is special, not associated with a char */
 		if (status & UART_OVERRUN_ERROR)
 			tty_insert_flip_char(tty, 0, TTY_OVERRUN);
+
+		if (status & UART_DCD)
+			usb_serial_handle_dcd_change(port, tty,
+				   priv->line_status & MSR_STATUS_LINE_DCD);
 	}
 
 	tty_insert_flip_string_fixed_flag(tty, data, tty_flag,