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+.. SPDX-License-Identifier: GPL-2.0
+
+=================
+Devlink Line card
+=================
+
+Background
+==========
+
+The ``devlink-linecard`` mechanism is targeted for manipulation of
+line cards that serve as a detachable PHY modules for modular switch
+system. Following operations are provided:
+
+ * Get a list of supported line card types.
+ * Provision of a slot with specific line card type.
+ * Get and monitor of line card state and its change.
+
+Line card according to the type may contain one or more gearboxes
+to mux the lanes with certain speed to multiple ports with lanes
+of different speed. Line card ensures N:M mapping between
+the switch ASIC modules and physical front panel ports.
+
+Overview
+========
+
+Each line card devlink object is created by device driver,
+according to the physical line card slots available on the device.
+
+Similar to splitter cable, where the device might have no way
+of detection of the splitter cable geometry, the device
+might not have a way to detect line card type. For that devices,
+concept of provisioning is introduced. It allows the user to:
+
+ * Provision a line card slot with certain line card type
+
+ - Device driver would instruct the ASIC to prepare all
+ resources accordingly. The device driver would
+ create all instances, namely devlink port and netdevices
+ that reside on the line card, according to the line card type
+ * Manipulate of line card entities even without line card
+ being physically connected or powered-up
+ * Setup splitter cable on line card ports
+
+ - As on the ordinary ports, user may provision a splitter
+ cable of a certain type, without the need to
+ be physically connected to the port
+ * Configure devlink ports and netdevices
+
+Netdevice carrier is decided as follows:
+
+ * Line card is not inserted or powered-down
+
+ - The carrier is always down
+ * Line card is inserted and powered up
+
+ - The carrier is decided as for ordinary port netdevice
+
+Line card state
+===============
+
+The ``devlink-linecard`` mechanism supports the following line card states:
+
+ * ``unprovisioned``: Line card is not provisioned on the slot.
+ * ``unprovisioning``: Line card slot is currently being unprovisioned.
+ * ``provisioning``: Line card slot is currently in a process of being provisioned
+ with a line card type.
+ * ``provisioning_failed``: Provisioning was not successful.
+ * ``provisioned``: Line card slot is provisioned with a type.
+ * ``active``: Line card is powered-up and active.
+
+The following diagram provides a general overview of ``devlink-linecard``
+state transitions::
+
+ +-------------------------+
+ | |
+ +----------------------------------> unprovisioned |
+ | | |
+ | +--------|-------^--------+
+ | | |
+ | | |
+ | +--------v-------|--------+
+ | | |
+ | | provisioning |
+ | | |
+ | +------------|------------+
+ | |
+ | +-----------------------------+
+ | | |
+ | +------------v------------+ +------------v------------+ +-------------------------+
+ | | | | ----> |
+ +----- provisioning_failed | | provisioned | | active |
+ | | | | <---- |
+ | +------------^------------+ +------------|------------+ +-------------------------+
+ | | |
+ | | |
+ | | +------------v------------+
+ | | | |
+ | | | unprovisioning |
+ | | | |
+ | | +------------|------------+
+ | | |
+ | +-----------------------------+
+ | |
+ +-----------------------------------------------+
+
+
+Example usage
+=============
+
+.. code:: shell
+
+ $ devlink lc show [ DEV [ lc LC_INDEX ] ]
+ $ devlink lc set DEV lc LC_INDEX [ { type LC_TYPE | notype } ]
+
+ # Show current line card configuration and status for all slots:
+ $ devlink lc
+
+ # Set slot 8 to be provisioned with type "16x100G":
+ $ devlink lc set pci/0000:01:00.0 lc 8 type 16x100G
+
+ # Set slot 8 to be unprovisioned:
+ $ devlink lc set pci/0000:01:00.0 lc 8 notype