USB: usbserial: mos7720: add support for parallel port on moschip 7715

Add support for the parallel port on the moschip MCS7715 device.  The port
registers itself with the parport subsystem as a low-level driver.  A separate
entry to the kernel configuration is added beneath that for the mos7720, to
avoid the need to link with the parport subsystem code for users who don't have
or don't want the parallel port.  Only compatibility mode is currently supported
(no ECP/EPP).  Tested with both moschip devices (7720 and 7715) on UP and SMP
hosts, including regression testing of serial port, concurrent operation of
serial and parallel ports, and various connect / disconnect scenarios.
Signed-off-by: NMike Dunn <mikedunn@newsguy.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Documentation/usb/usb-serial.txt

@@ -440,6 +440,22 @@ Winchiphead CH341 Driver
   For any questions or problems with this driver, please contact
   frank@kingswood-consulting.co.uk.
 
+Moschip MCS7720, MCS7715 driver
+
+  These chips are present in devices sold by various manufacturers, such as Syba
+  and Cables Unlimited.  There may be others.  The 7720 provides two serial
+  ports, and the 7715 provides one serial and one standard PC parallel port.
+  Support for the 7715's parallel port is enabled by a separate option, which
+  will not appear unless parallel port support is first enabled at the top-level
+  of the Device Drivers config menu.  Currently only compatibility mode is
+  supported on the parallel port (no ECP/EPP).
+
+  TODO:
+    - Implement ECP/EPP modes for the parallel port.
+    - Baud rates higher than 115200 are currently broken.
+    - Devices with a single serial port based on the Moschip MCS7703 may work
+      with this driver with a simple addition to the usb_device_id table.  I
+      don't have one of these devices, so I can't say for sure.
 
 Generic Serial driver
 

drivers/usb/serial/Kconfig

@@ -425,6 +425,17 @@ config USB_SERIAL_MOS7720
 	  To compile this driver as a module, choose M here: the
 	  module will be called mos7720.
 
+if USB_SERIAL_MOS7720
+config USB_SERIAL_MOS7715_PARPORT
+	bool "Support for parallel port on the Moschip 7715"
+	select PARPORT_NOT_PC
+	depends on PARPORT
+	---help---
+	Say Y if you have a Moschip 7715 device and would like to use
+	the parallel port it provides.  The port will register with
+	the parport subsystem as a low-level driver.
+endif
+
 config USB_SERIAL_MOS7840
 	tristate "USB Moschip 7840/7820 USB Serial Driver"
 	---help---