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+========================
+Linux Switchtec Support
+========================
+
+Microsemi's "Switchtec" line of PCI switch devices is already
+supported by the kernel with standard PCI switch drivers. However, the
+Switchtec device advertises a special management endpoint which
+enables some additional functionality. This includes:
+
+* Packet and Byte Counters
+* Firmware Upgrades
+* Event and Error logs
+* Querying port link status
+* Custom user firmware commands
+
+The switchtec kernel module implements this functionality.
+
+
+Interface
+=========
+
+The primary means of communicating with the Switchtec management firmware is
+through the Memory-mapped Remote Procedure Call (MRPC) interface.
+Commands are submitted to the interface with a 4-byte command
+identifier and up to 1KB of command specific data. The firmware will
+respond with a 4-byte return code and up to 1KB of command-specific
+data. The interface only processes a single command at a time.
+
+
+Userspace Interface
+===================
+
+The MRPC interface will be exposed to userspace through a simple char
+device: /dev/switchtec#, one for each management endpoint in the system.
+
+The char device has the following semantics:
+
+* A write must consist of at least 4 bytes and no more than 1028 bytes.
+ The first 4 bytes will be interpreted as the Command ID and the
+ remainder will be used as the input data. A write will send the
+ command to the firmware to begin processing.
+
+* Each write must be followed by exactly one read. Any double write will
+ produce an error and any read that doesn't follow a write will
+ produce an error.
+
+* A read will block until the firmware completes the command and return
+ the 4-byte Command Return Value plus up to 1024 bytes of output
+ data. (The length will be specified by the size parameter of the read
+ call -- reading less than 4 bytes will produce an error.)
+
+* The poll call will also be supported for userspace applications that
+ need to do other things while waiting for the command to complete.
+
+The following IOCTLs are also supported by the device:
+
+* SWITCHTEC_IOCTL_FLASH_INFO - Retrieve firmware length and number
+ of partitions in the device.
+
+* SWITCHTEC_IOCTL_FLASH_PART_INFO - Retrieve address and lengeth for
+ any specified partition in flash.
+
+* SWITCHTEC_IOCTL_EVENT_SUMMARY - Read a structure of bitmaps
+ indicating all uncleared events.
+
+* SWITCHTEC_IOCTL_EVENT_CTL - Get the current count, clear and set flags
+ for any event. This ioctl takes in a switchtec_ioctl_event_ctl struct
+ with the event_id, index and flags set (index being the partition or PFF
+ number for non-global events). It returns whether the event has
+ occurred, the number of times and any event specific data. The flags
+ can be used to clear the count or enable and disable actions to
+ happen when the event occurs.
+ By using the SWITCHTEC_IOCTL_EVENT_FLAG_EN_POLL flag,
+ you can set an event to trigger a poll command to return with
+ POLLPRI. In this way, userspace can wait for events to occur.
+
+* SWITCHTEC_IOCTL_PFF_TO_PORT and SWITCHTEC_IOCTL_PORT_TO_PFF convert
+ between PCI Function Framework number (used by the event system)
+ and Switchtec Logic Port ID and Partition number (which is more
+ user friendly).
+
+
+Non-Transparent Bridge (NTB) Driver
+===================================
+
+An NTB hardware driver is provided for the Switchtec hardware in
+ntb_hw_switchtec. Currently, it only supports switches configured with
+exactly 2 NT partitions and zero or more non-NT partitions. It also requires
+the following configuration settings:
+
+* Both NT partitions must be able to access each other's GAS spaces.
+ Thus, the bits in the GAS Access Vector under Management Settings
+ must be set to support this.
+* Kernel configuration MUST include support for NTB (CONFIG_NTB needs
+ to be set)
+
+NT EP BAR 2 will be dynamically configured as a Direct Window, and
+the configuration file does not need to configure it explicitly.
+
+Please refer to Documentation/driver-api/ntb.rst in Linux source tree for an overall
+understanding of the Linux NTB stack. ntb_hw_switchtec works as an NTB
+Hardware Driver in this stack.