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+AppliedMicro X-Gene SOC Queue Manager/Traffic Manager Document
+
+Copyright (c) 2013 Applied Micro Circuits Corporation.
+Author: Ravi Patel <rapatel@apm.com>
+
+This program is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License version 2 as published by
+the Free Software Foundation.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU General Public License for more details.
+
+
+Overview:
+QMTM is a device which interacts with CPU, Ethernet, PktDMA and Security
+subsystems through AXI BUS. Its centralized resource manager/driver exports
+APIs for CPU, Ethernet, PktDMA and Security subsystems to
+1. Initialize & allocate queue & pbn.
+2. Read queue state so that subsystems driver knows how much more work it can
+ offload to its subsystem.
+3. Apply QoS for subsystems on their queues.
+
+Layout:
+The layout represents run-time flow of messages between Ethernet subsystem, CPU
+and QMTM in APM X-Gene SOC. PktDMA and Security subsystems interfaces with QMTM
+in the same way as Ethernet.
+
+
+ CPU
+ o-------------------------o
+ | |
+ +----|[2] {5}|----+
+ | | [1] {4} | |
+Register | o------+-----------+------o | Register
+Write | CPU WR | | CPU RD | Write
+to start v MSG v ^ MSG v to notify
+packet | | DDR | | packet
+transmit | o--------+-----o-----+--------o | received
+ | | Q0 M . M M | M M . M Q1 | |
+ | | for S . S S | S S . S for | |
+ | | ETH G . G G | G G . G ETH | |
+ | | TX n . 2 1 | 1 2 . n RX | |
+ | o----------+---o---+----------o |
+ | | | |
+ v v ^ v
+ | | | |
+o--------|-------------|-------|-------------|--------o
+| | | | | | Coherent
+| v v ^ v | I/O
+| | | | | | BUS
+o--------|-------------|-------|-------------|--------o
+ | [3] | | {3} |
+ v QMTM RD v ^ QMTM WR v
+ | MSG | | MSG |
+ o----+----o--------+---o---+--------o----+----o
+ | Queue 0 | | | Queue 1 |
+ | Command o ETH PBN 0 o CPU PBN 0 o Command | Queue Manager/
+ | Register| | |Register | Traffic Manager
+ o---------o---+--------o--------+---o---------o
+ | |
+ v ^
+Ethernet RD MSG | [4] ETH {2} | Ethernet WR MSG
+from its PBN o---+-----------------+---o to CPU PBN
+ | |
+ | Egress MAC Ingress MAC |
+ | [5] {1} |
+ o------|-----------|------o
+ v ^
+ | |
+ TX Data RX Data
+
+Transmit Flow
+[1] CPU (Ethernet driver) prepares 32 byte Ethernet egress work message and
+ enqueues the message to the queue in DDR.
+[2] CPU (Ethernet driver) notifies QMTM that there is a message enqueued in
+ Ethernet transmit queue (e.g. Q0).
+[3] QMTM prefetches the Ethernet egress work messages into Ethernet PBN
+ (e.g. ETH PBN 0).
+[4] Ethernet reads work messages from its PBN.
+[5] Ethernet DMAs payload from DDR to its egress FIFO and transmits data out.
+
+Receive Flow
+{1} Ethernet receives data and DMAs payload from its ingress FIFO to DDR and
+ prepares a Ethernet ingress work message.
+{2} Ethernet pushes work message to QMTM.
+{3} QMTM prefetches the Ethernet ingress work messages into CPU PBN
+ (e.g. CPU PBN 0) and then interrupts CPU.
+{4} CPU (Ethernet driver) dequeues the 32 bytes Ethernet ingress work message
+ from the queue in DDR.
+{5} CPU (Ethernet driver) notifies QMTM that it dequeued a message from
+ Ethernet receive queue (e.g. Q1).
+
+
+Definition:
+1. QMTM (Queue/Traffic Manager)
+ QMTM manages queues and pbns for CPU, Ethernet, PktDMA and Security
+ Subsystems. It also performs flow control and QoS on queues.
+
+2. Slave/Client/Agent
+ Ethernet, PktDMA (XOR Engine) and Security Engine Subsystems & CPU whose
+ queues and pbn are managed by QMTM are called slave/client/agent.
+
+3. Queue
+ Queue is circular FIFO memory for QMTM hardware in which a 16 bytes,
+ 32 bytes or 64 bytes message is dequeued OR enqueued between CPU and
+ Ethernet, PktDMA and Security Engine Subsystems.
+
+4. PB
+ Each subsystem in the APM X-Gene SoC device has a prefetch buffer for
+ storing messages in order to pipeline the QMTM processing latency with the
+ subsystem processing latency. The number of buffers prefetched depends on
+ the QM/TM processing latency and the subsystem data rate.
+
+ There are multiple PB for a subsystem, each PB is assigned a number which is
+ called PBN. Each subsystem and CPU can have max 32 pbns, however QMTM limits
+ how many pbns it supports for each subsystem.
+
+5. Message
+ The subsystems in the APM X-Gene SoC communicate with a central Queue Manager
+ (QM) that manages all the messages queued to the subsystems. The subsystems
+ communicate with the QM using messages that include information about the
+ work to be performed and the location of the buffers or data on which the
+ work is to be performed.
+
+ A message consists of 16, 32 or 64 bytes which resides in a queue. A message
+ which is
+ a. 16 bytes contains information of data buffer, length, etc. allocated by
+ subsystem driver.
+ b. 32 or 64 bytes contains information about the work to be done for a
+ subsystem. Each subsystem defines its own format of work message.
+
+ Each subsystem defines their own format of work message. A message (or queue
+ descriptor) has attribute fields (QMTM specific) which are common for all
+ subsystem work messages. The remaining fields of a message are specific to
+ subsystem. QMTM device doesn't have any knowledge of these subsystems
+ specific fields and the data operation which subsystem is going to perform
+ using these fields.
+
+ e.g.
+ 1. Ethernet work message includes data address & length which is used by
+ Ethernet DMA engine for copying the data to/from its internal FIFO.
+ 2. PktDMA work message includes multiple data addresses & lengths for
+ doing scatter/gather, XOR operations and result data address/es to give
+ back result to the CPU (driver).
+ 3. Security work message includes data address & length for doing encryption
+ or decryption, the type of encryption or decryption and result data
+ address to give back result to the CPU (driver).