usb: Add driver for Altus Metrum ChaosKey device (v2)

This is a hardware random number generator. The driver provides both a
/dev/chaoskeyX entry and hooks the entropy source up to the kernel
hwrng interface. More information about the device can be found at
http://chaoskey.org

The USB ID for ChaosKey was allocated from the OpenMoko USB vendor
space and is visible as 'USBtrng' here:

http://wiki.openmoko.org/wiki/USB_Product_IDs

v2: Respond to review from Oliver Neukum <oneukum@suse.de>

 * Delete extensive debug infrastructure and replace it with calls to
   dev_dbg.

 * Allocate I/O buffer separately from device structure to obey
   requirements for non-coherant architectures.

 * Initialize mutexes before registering device to ensure that open
   cannot be invoked before the device is ready to proceed.

 * Return number of bytes read instead of -EINTR when partial read
   operation is aborted due to a signal.

 * Make sure device mutex is unlocked in read error paths.

 * Add MAINTAINERS entry for the driver

Signed-off-by: Keith Packard <keithp@keithp.com>
Cc: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: keith-packard

MAINTAINERS

@@ -10129,6 +10129,12 @@ S:	Maintained
 F:	drivers/net/usb/cdc_*.c
 F:	include/uapi/linux/usb/cdc.h
 
+USB CHAOSKEY DRIVER
+M:	Keith Packard <keithp@keithp.com>
+L:	linux-usb@vger.kernel.org
+S:	Maintained
+F:	drivers/usb/misc/chaoskey.c
+
 USB CYPRESS C67X00 DRIVER
 M:	Peter Korsgaard <jacmet@sunsite.dk>
 L:	linux-usb@vger.kernel.org

drivers/usb/misc/Kconfig

@@ -255,3 +255,15 @@ config USB_LINK_LAYER_TEST
 	  This driver is for generating specific traffic for Super Speed Link
 	  Layer Test Device. Say Y only when you want to conduct USB Super Speed
 	  Link Layer Test for host controllers.
+
+config USB_CHAOSKEY
+	tristate "ChaosKey random number generator driver support"
+	help
+	  Say Y here if you want to connect an AltusMetrum ChaosKey to
+	  your computer's USB port. The ChaosKey is a hardware random
+	  number generator which hooks into the kernel entropy pool to
+	  ensure a large supply of entropy for /dev/random and
+	  /dev/urandom and also provides direct access via /dev/chaoskeyX
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called chaoskey.

drivers/usb/misc/Makefile

@@ -25,6 +25,7 @@ obj-$(CONFIG_USB_USS720)		+= uss720.o
 obj-$(CONFIG_USB_SEVSEG)		+= usbsevseg.o
 obj-$(CONFIG_USB_YUREX)			+= yurex.o
 obj-$(CONFIG_USB_HSIC_USB3503)		+= usb3503.o
+obj-$(CONFIG_USB_CHAOSKEY)		+= chaoskey.o
 
 obj-$(CONFIG_USB_SISUSBVGA)		+= sisusbvga/
 obj-$(CONFIG_USB_LINK_LAYER_TEST)	+= lvstest.o