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+.. SPDX-License-Identifier: GPL-2.0+
+======================================================
+IBM Virtual Management Channel Kernel Driver (IBMVMC)
+======================================================
+
+:Authors:
+	Dave Engebretsen <engebret@us.ibm.com>,
+	Adam Reznechek <adreznec@linux.vnet.ibm.com>,
+	Steven Royer <seroyer@linux.vnet.ibm.com>,
+	Bryant G. Ly <bryantly@linux.vnet.ibm.com>,
+
+Introduction
+============
+
+Note: Knowledge of virtualization technology is required to understand
+this document.
+
+A good reference document would be:
+
+https://openpowerfoundation.org/wp-content/uploads/2016/05/LoPAPR_DRAFT_v11_24March2016_cmt1.pdf
+
+The Virtual Management Channel (VMC) is a logical device which provides an
+interface between the hypervisor and a management partition. This interface
+is like a message passing interface. This management partition is intended
+to provide an alternative to systems that use a Hardware Management
+Console (HMC) - based system management.
+
+The primary hardware management solution that is developed by IBM relies
+on an appliance server named the Hardware Management Console (HMC),
+packaged as an external tower or rack-mounted personal computer. In a
+Power Systems environment, a single HMC can manage multiple POWER
+processor-based systems.
+
+Management Application
+----------------------
+
+In the management partition, a management application exists which enables
+a system administrator to configure the system’s partitioning
+characteristics via a command line interface (CLI) or Representational
+State Transfer Application (REST API's).
+
+The management application runs on a Linux logical partition on a
+POWER8 or newer processor-based server that is virtualized by PowerVM.
+System configuration, maintenance, and control functions which
+traditionally require an HMC can be implemented in the management
+application using a combination of HMC to hypervisor interfaces and
+existing operating system methods. This tool provides a subset of the
+functions implemented by the HMC and enables basic partition configuration.
+The set of HMC to hypervisor messages supported by the management
+application component are passed to the hypervisor over a VMC interface,
+which is defined below.
+
+The VMC enables the management partition to provide basic partitioning
+functions:
+
+- Logical Partitioning Configuration
+- Start, and stop actions for individual partitions
+- Display of partition status
+- Management of virtual Ethernet
+- Management of virtual Storage
+- Basic system management
+
+Virtual Management Channel (VMC)
+--------------------------------
+
+A logical device, called the Virtual Management Channel (VMC), is defined
+for communicating between the management application and the hypervisor. It
+basically creates the pipes that enable virtualization management
+software. This device is presented to a designated management partition as
+a virtual device.
+
+This communication device uses Command/Response Queue (CRQ) and the
+Remote Direct Memory Access (RDMA) interfaces. A three-way handshake is
+defined that must take place to establish that both the hypervisor and
+management partition sides of the channel are running prior to
+sending/receiving any of the protocol messages.
+
+This driver also utilizes Transport Event CRQs. CRQ messages are sent
+when the hypervisor detects one of the peer partitions has abnormally
+terminated, or one side has called H_FREE_CRQ to close their CRQ.
+Two new classes of CRQ messages are introduced for the VMC device. VMC
+Administrative messages are used for each partition using the VMC to
+communicate capabilities to their partner. HMC Interface messages are used
+for the actual flow of HMC messages between the management partition and
+the hypervisor. As most HMC messages far exceed the size of a CRQ buffer,
+a virtual DMA (RMDA) of the HMC message data is done prior to each HMC
+Interface CRQ message. Only the management partition drives RDMA
+operations; hypervisors never directly cause the movement of message data.
+
+
+Terminology
+-----------
+RDMA
+        Remote Direct Memory Access is DMA transfer from the server to its
+        client or from the server to its partner partition. DMA refers
+        to both physical I/O to and from memory operations and to memory
+        to memory move operations.
+CRQ
+        Command/Response Queue a facility which is used to communicate
+        between partner partitions. Transport events which are signaled
+        from the hypervisor to partition are also reported in this queue.
+
+Example Management Partition VMC Driver Interface
+=================================================
+
+This section provides an example for the management application
+implementation where a device driver is used to interface to the VMC
+device. This driver consists of a new device, for example /dev/ibmvmc,
+which provides interfaces to open, close, read, write, and perform
+ioctl’s against the VMC device.
+
+VMC Interface Initialization
+----------------------------
+
+The device driver is responsible for initializing the VMC when the driver
+is loaded. It first creates and initializes the CRQ. Next, an exchange of
+VMC capabilities is performed to indicate the code version and number of
+resources available in both the management partition and the hypervisor.
+Finally, the hypervisor requests that the management partition create an
+initial pool of VMC buffers, one buffer for each possible HMC connection,
+which will be used for management application  session initialization.
+Prior to completion of this initialization sequence, the device returns
+EBUSY to open() calls. EIO is returned for all open() failures.
+
+::
+
+        Management Partition		Hypervisor
+                        CRQ INIT
+        ---------------------------------------->
+        	   CRQ INIT COMPLETE
+        <----------------------------------------
+        	      CAPABILITIES
+        ---------------------------------------->
+        	 CAPABILITIES RESPONSE
+        <----------------------------------------
+              ADD BUFFER (HMC IDX=0,1,..)         _
+        <----------------------------------------  |
+        	  ADD BUFFER RESPONSE              | - Perform # HMCs Iterations
+        ----------------------------------------> -
+
+VMC Interface Open
+------------------
+
+After the basic VMC channel has been initialized, an HMC session level
+connection can be established. The application layer performs an open() to
+the VMC device and executes an ioctl() against it, indicating the HMC ID
+(32 bytes of data) for this session. If the VMC device is in an invalid
+state, EIO will be returned for the ioctl(). The device driver creates a
+new HMC session value (ranging from 1 to 255) and HMC index value (starting
+at index 0 and ranging to 254) for this HMC ID. The driver then does an
+RDMA of the HMC ID to the hypervisor, and then sends an Interface Open
+message to the hypervisor to establish the session over the VMC. After the
+hypervisor receives this information, it sends Add Buffer messages to the
+management partition to seed an initial pool of buffers for the new HMC
+connection. Finally, the hypervisor sends an Interface Open Response
+message, to indicate that it is ready for normal runtime messaging. The
+following illustrates this VMC flow:
+
+::
+
+        Management Partition             Hypervisor
+        	      RDMA HMC ID
+        ---------------------------------------->
+        	    Interface Open
+        ---------------------------------------->
+        	      Add Buffer                  _
+        <----------------------------------------  |
+        	  Add Buffer Response              | - Perform N Iterations
+        ----------------------------------------> -
+        	Interface Open Response
+        <----------------------------------------
+
+VMC Interface Runtime
+---------------------
+
+During normal runtime, the management application and the hypervisor
+exchange HMC messages via the Signal VMC message and RDMA operations. When
+sending data to the hypervisor, the management application performs a
+write() to the VMC device, and the driver RDMA’s the data to the hypervisor
+and then sends a Signal Message. If a write() is attempted before VMC
+device buffers have been made available by the hypervisor, or no buffers
+are currently available, EBUSY is returned in response to the write(). A
+write() will return EIO for all other errors, such as an invalid device
+state. When the hypervisor sends a message to the management, the data is
+put into a VMC buffer and an Signal Message is sent to the VMC driver in
+the management partition. The driver RDMA’s the buffer into the partition
+and passes the data up to the appropriate management application via a
+read() to the VMC device. The read() request blocks if there is no buffer
+available to read. The management application may use select() to wait for
+the VMC device to become ready with data to read.
+
+::
+
+        Management Partition             Hypervisor
+        		MSG RDMA
+        ---------------------------------------->
+        		SIGNAL MSG
+        ---------------------------------------->
+        		SIGNAL MSG
+        <----------------------------------------
+        		MSG RDMA
+        <----------------------------------------
+
+VMC Interface Close
+-------------------
+
+HMC session level connections are closed by the management partition when
+the application layer performs a close() against the device. This action
+results in an Interface Close message flowing to the hypervisor, which
+causes the session to be terminated. The device driver must free any
+storage allocated for buffers for this HMC connection.
+
+::
+
+        Management Partition             Hypervisor
+        	     INTERFACE CLOSE
+        ---------------------------------------->
+                INTERFACE CLOSE RESPONSE
+        <----------------------------------------
+
+Additional Information
+======================
+
+For more information on the documentation for CRQ Messages, VMC Messages,
+HMC interface Buffers, and signal messages please refer to the Linux on
+Power Architecture Platform Reference. Section F.