.. SPDX-License-Identifier: GPL-2.0

==============
Devlink Region
==============

``devlink`` regions enable access to driver defined address regions using
devlink.

Each device can create and register its own supported address regions. The
region can then be accessed via the devlink region interface.

Region snapshots are collected by the driver, and can be accessed via read
or dump commands. This allows future analysis on the created snapshots.
Regions may optionally support triggering snapshots on demand.

Snapshot identifiers are scoped to the devlink instance, not a region.
All snapshots with the same snapshot id within a devlink instance
correspond to the same event.

The major benefit to creating a region is to provide access to internal
address regions that are otherwise inaccessible to the user.

Regions may also be used to provide an additional way to debug complex error
states, but see also Documentation/networking/devlink/devlink-health.rst

Regions may optionally support capturing a snapshot on demand via the
``DEVLINK_CMD_REGION_NEW`` netlink message. A driver wishing to allow
requested snapshots must implement the ``.snapshot`` callback for the region
in its ``devlink_region_ops`` structure. If snapshot id is not set in
the ``DEVLINK_CMD_REGION_NEW`` request kernel will allocate one and send
the snapshot information to user space.

Regions may optionally allow directly reading from their contents without a
snapshot. Direct read requests are not atomic. In particular a read request
of size 256 bytes or larger will be split into multiple chunks. If atomic
access is required, use a snapshot. A driver wishing to enable this for a
region should implement the ``.read`` callback in the ``devlink_region_ops``
structure. User space can request a direct read by using the
``DEVLINK_ATTR_REGION_DIRECT`` attribute instead of specifying a snapshot
id.

example usage
-------------

.. code:: shell

    $ devlink region help
    $ devlink region show [ DEV/REGION ]
    $ devlink region del DEV/REGION snapshot SNAPSHOT_ID
    $ devlink region dump DEV/REGION [ snapshot SNAPSHOT_ID ]
    $ devlink region read DEV/REGION [ snapshot SNAPSHOT_ID ] address ADDRESS length length

    # Show all of the exposed regions with region sizes:
    $ devlink region show
    pci/0000:00:05.0/cr-space: size 1048576 snapshot [1 2] max 8
    pci/0000:00:05.0/fw-health: size 64 snapshot [1 2] max 8

    # Delete a snapshot using:
    $ devlink region del pci/0000:00:05.0/cr-space snapshot 1

    # Request an immediate snapshot, if supported by the region
    $ devlink region new pci/0000:00:05.0/cr-space
    pci/0000:00:05.0/cr-space: snapshot 5

    # Dump a snapshot:
    $ devlink region dump pci/0000:00:05.0/fw-health snapshot 1
    0000000000000000 0014 95dc 0014 9514 0035 1670 0034 db30
    0000000000000010 0000 0000 ffff ff04 0029 8c00 0028 8cc8
    0000000000000020 0016 0bb8 0016 1720 0000 0000 c00f 3ffc
    0000000000000030 bada cce5 bada cce5 bada cce5 bada cce5

    # Read a specific part of a snapshot:
    $ devlink region read pci/0000:00:05.0/fw-health snapshot 1 address 0 length 16
    0000000000000000 0014 95dc 0014 9514 0035 1670 0034 db30

    # Read from the region without a snapshot
    $ devlink region read pci/0000:00:05.0/fw-health address 16 length 16
    0000000000000010 0000 0000 ffff ff04 0029 8c00 0028 8cc8

As regions are likely very device or driver specific, no generic regions are
defined. See the driver-specific documentation files for information on the
specific regions a driver supports.
