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

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

v2: Respond to review from Oliver Neukum <>

 * Delete extensive debug infrastructure and replace it with calls to

 * 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 <>
4 files changed