RapidIO subsystem Channelized Messaging character device driver (rio_cm.c)
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  Version History:
  ----------------
    1.0.0 - Initial driver release.
  
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  I. Overview
  
  This device driver is the result of collaboration within the RapidIO.org
  Software Task Group (STG) between Texas Instruments, Prodrive Technologies,
  Nokia Networks, BAE and IDT.  Additional input was received from other members
  of RapidIO.org.
  
  The objective was to create a character mode driver interface which exposes
  messaging capabilities of RapidIO endpoint devices (mports) directly
  to applications, in a manner that allows the numerous and varied RapidIO
  implementations to interoperate.
  
  This driver (RIO_CM) provides to user-space applications shared access to
  RapidIO mailbox messaging resources.
  
  RapidIO specification (Part 2) defines that endpoint devices may have up to four
  messaging mailboxes in case of multi-packet message (up to 4KB) and
  up to 64 mailboxes if single-packet messages (up to 256 B) are used. In addition
  to protocol definition limitations, a particular hardware implementation can
  have reduced number of messaging mailboxes.  RapidIO aware applications must
  therefore share the messaging resources of a RapidIO endpoint.
  
  Main purpose of this device driver is to provide RapidIO mailbox messaging
  capability to large number of user-space processes by introducing socket-like
  operations using a single messaging mailbox.  This allows applications to
  use the limited RapidIO messaging hardware resources efficiently.
  
  Most of device driver's operations are supported through 'ioctl' system calls.
  
  When loaded this device driver creates a single file system node named rio_cm
  in /dev directory common for all registered RapidIO mport devices.
  
  Following ioctl commands are available to user-space applications:
  
  - RIO_CM_MPORT_GET_LIST : Returns to caller list of local mport devices that
      support messaging operations (number of entries up to RIO_MAX_MPORTS).
      Each list entry is combination of mport's index in the system and RapidIO
      destination ID assigned to the port.
  - RIO_CM_EP_GET_LIST_SIZE : Returns number of messaging capable remote endpoints
      in a RapidIO network associated with the specified mport device.
  - RIO_CM_EP_GET_LIST : Returns list of RapidIO destination IDs for messaging
      capable remote endpoints (peers) available in a RapidIO network associated
      with the specified mport device.
  - RIO_CM_CHAN_CREATE : Creates RapidIO message exchange channel data structure
      with channel ID assigned automatically or as requested by a caller.
  - RIO_CM_CHAN_BIND : Binds the specified channel data structure to the specified
      mport device.
  - RIO_CM_CHAN_LISTEN : Enables listening for connection requests on the specified
      channel.
  - RIO_CM_CHAN_ACCEPT : Accepts a connection request from peer on the specified
      channel. If wait timeout for this request is specified by a caller it is
      a blocking call. If timeout set to 0 this is non-blocking call - ioctl
      handler checks for a pending connection request and if one is not available
      exits with -EGAIN error status immediately.
  - RIO_CM_CHAN_CONNECT : Sends a connection request to a remote peer/channel.
  - RIO_CM_CHAN_SEND : Sends a data message through the specified channel.
      The handler for this request assumes that message buffer specified by
      a caller includes the reserved space for a packet header required by
      this driver.
  - RIO_CM_CHAN_RECEIVE : Receives a data message through a connected channel.
      If the channel does not have an incoming message ready to return this ioctl
      handler will wait for new message until timeout specified by a caller
      expires. If timeout value is set to 0, ioctl handler uses a default value
      defined by MAX_SCHEDULE_TIMEOUT.
  - RIO_CM_CHAN_CLOSE : Closes a specified channel and frees associated buffers.
      If the specified channel is in the CONNECTED state, sends close notification
      to the remote peer.
  
  The ioctl command codes and corresponding data structures intended for use by
  user-space applications are defined in 'include/uapi/linux/rio_cm_cdev.h'.
  
  II. Hardware Compatibility
  
  This device driver uses standard interfaces defined by kernel RapidIO subsystem
  and therefore it can be used with any mport device driver registered by RapidIO
  subsystem with limitations set by available mport HW implementation of messaging
  mailboxes.
  
  III. Module parameters
  
  - 'dbg_level' - This parameter allows to control amount of debug information
          generated by this device driver. This parameter is formed by set of
          bit masks that correspond to the specific functional block.
          For mask definitions see 'drivers/rapidio/devices/rio_cm.c'
          This parameter can be changed dynamically.
          Use CONFIG_RAPIDIO_DEBUG=y to enable debug output at the top level.
  
  - 'cmbox' - Number of RapidIO mailbox to use (default value is 1).
          This parameter allows to set messaging mailbox number that will be used
          within entire RapidIO network. It can be used when default mailbox is
          used by other device drivers or is not supported by some nodes in the
          RapidIO network.
  
  - 'chstart' - Start channel number for dynamic assignment. Default value - 256.
          Allows to exclude channel numbers below this parameter from dynamic
          allocation to avoid conflicts with software components that use
          reserved predefined channel numbers.
  
  IV. Known problems
  
    None.
  
  V. User-space Applications and API Library
  
  Messaging API library and applications that use this device driver are available
  from RapidIO.org.
  
  VI. TODO List
  
  - Add support for system notification messages (reserved channel 0).