.. _device_types:

Device types
############

When adding devices, there is a decision to be made about what
qualifies as a distinct device type and what does not. A different
type of device can mean different things, including:

* different hardware.
* different access methods (typically, bootloaders).
* different test writer use cases, e.g. testing firmware or testing user space
  performance.

However, a slight or incremental change to hardware does not
necessarily mean that the updated device must be a different device
type. Even if a change adds significant functionality, e.g. if USB
hot-plug becomes available on revision C, that does not necessarily
mean that revision C should be a different device type compared to to
revision A and B.

Typically, the distinction between two device types comes down to
whether the two devices can be driven in the same way at bootloader
level, from initial power on.

Another example to consider is :term:`DTB` support. If there is more
than one DTB available for a particular family of devices, this will
probably lead to multiple different device types. Also consider
whether all devices of the proposed device type can boot all DTBs
available for that type.

In the end, LAVA lab administrators are free to make their own choices
about what qualifies as a distinct device type. Some factors to
consider in this judgement call include:

* **Interchangeable jobs**: Does a single health check work for all
  devices of this type? It is recommended to always test all of the
  supported boot methods of a device type during a single health check
  test job.

* **Interchangeable bootloaders**: Some devices can change bootloader
  type within a single job, allowing a single device type to meet the
  needs of a variety of different use cases. There are issues to
  consider here:

  * **Latency**: Changing the bootloader on every test job may have
    significant costs in terms of job runtime. This is particularly
    noticeable in the length of time required before the actual test
    can start. In such cases, it may be worth considering a
    **sub-type** instead.

    .. seealso:: :ref:`sub_device_types`

  * **Hardware lifetime of the device**: Frequently, writing a new
    bootloader may cause problems on some devices where the bootloader
    may be stored on media which can only be written a limited number
    of times.

* **Multi-stage bootloaders**: Some devices may have a first or second
  stage bootloader which can then load different higher level
  bootloaders. This is often described as a chained
  bootloader. Depending on the types of tests desired, some admins may
  choose to expose a choice of higher level bootloader or may choose
  to not allow interrupting the lower stage(s). For example, some test
  writers will want to test the firmware and some test writers will
  only want to interact with GRUB or later.

* **Equivalence**: Different labs may make different decisions - if you
  are looking to work with an existing lab, try to follow their device
  type layout and ask about how a new device should be classified
  before committing to a decision in your own lab.

* **Test requirements**: Talk to the test writers and establish
  whether an apparent hardware difference is sufficient that the
  device needs to be described using a different device type. Also
  consider whether the test writer requirements are going to change
  over time. Just because there is no current desire to test the
  experimental bootloader available on one device, this does not mean
  that this will remain unused in a year.

* **Scheduling**: If two devices have the same device type, each
  device needs to be able to run any test job submitted for that
  device type. There is support within LAVA for encoding small
  differences between devices within a single device type - see
  :term:`device tag`.

* **LAVA support**: There are some considerations which are
  constrained by LAVA support, For example, the V1 dispatcher had a
  ``kvm`` device type but the improved device configuration design in
  V2 made this unnecessary. If the only factor requiring two device
  types is LAVA support, please :ref:`talk to us <getting_support>`.

Permanency
==========

Once a device type has been implemented, devices added and test jobs run, it
can be awkward to change the device type. Changing the device type later will
make it difficult for users to find test results across this and other devices
and may cause significant issues with data consistency.

Separate device types can also complicate queries and result reporting -
combining two devices which eventually end up being different device types
causes issues with a loss of history when the split is finally made.

It is not a good idea to split device types arbitrarily - sooner or later there
may be a requirement to look at the results of jobs across both types and
having an unnecessary device type is confusing for test writers. Use a
:term:`device tag` to describe small differences between devices of the same
device type where it makes sense.

.. seealso:: :ref:`device_type_metadata`.

.. _sub_device_types:

Device sub-types
================

A balance needs to be drawn between test jobs which simply want to use a
known working build of the firmware and/or bootloader and those test jobs
where the latest build is relevant to the success or failure of the test
itself. Different test writers may have different requirements here.

An example of sub-types could be ``juno-uboot`` compared to
``juno-firmware``. Consider the principle of *test one thing at a
time*. Let userspace test jobs run without needing to change the
bootloader, and let bootloader test jobs have the ability to update by
separating the device type into two sub-types.

Think about device integration here. You need to be able to interrupt the boot
process at a level below whatever you are exposing to test writers. For
example, to offer test writers the ability to modify and test the firmware, the
platform **must** offer a way to replace the firmware in an automatable manner.

.. _naming_device_types:

Choosing a name for a device type
=================================

There are some considerations for the names of a device type in LAVA.

* The name of the device type in the database will be used as part of
  the URL of the page covering details of that device type, so the
  name **must not** include characters that would be encoded in a
  URL. This includes whitespace, UTF-8 characters, brackets and other
  common punctuation characters.

* Hyphens and underscores are supported.

* In general, the name should represent the hardware in a way that
  uniquely separates that type from similar hardware, e.g. panda and
  panda-es or imx6q-wandboard instead of just 'wandboard'.

* Each type has a description which can be used to provide
  lab-specific information, so the name does not have to include all
  details.

* Check other LAVA instances, especially if your instance is likely to
  need to work with other instances with a single frontend (like
  kernelci.org)

* Choose a sensible, descriptive name that will make sense to test
  writers. For example, ``panda`` or ``panda-es`` instead of
  ``panda1`` or ``panda2``.

.. index:: template mismatch

.. _template_mismatch:

Matching the template
---------------------

.. # comment: prevent this in the submission API once V1 jobs are rejected.

The name of a device type does not need to match an available template, however
the :term:`device dictionary` for all devices **must** ``extend`` a template
file which exists on the instance. Templates are a lot more than configuration.
The format supports conditional logic, inheritance and other features of code.
On the master, device type templates are configured using :term:`jinja2` files
in the directory::

 /etc/lava-server/dispatcher-config/device-types/

When creating a new device type, it is recommended to add the new template
file first and **use version control** to track changes then copy the template
file to the system location.

.. warning:: Adding a new device type template is the most complex
  part of administering a LAVA instance and it can be a lot of work
  (sometimes several months) to integrate a completely new device into
  LAVA. V2 offers a different and wider range of support to what was
  available in V1, but some devices may still need new support to be
  written directly within the ``lava-dispatcher`` code. **It may not
  always be possible to automate a new device**, depending on how the
  device connects to LAVA, how the device is powered and whether the
  software on the device allows the device to be controlled remotely.

.. seealso:: :ref:`adding_new_device_types` and :ref:`creating new device type
   templates <developing_device_type_templates>`.

.. index:: device type examples

.. _example_device_types:

Example device types
====================

* The ``panda`` and ``panda-es`` device types are separate in the Cambridge
  LAVA lab. When originally introduced, there was an expectation that the
  hardware differences between the devices would be relevant to how the jobs
  were constructed. As it turned out, no such difference was actually exploited
  by the test writers.

* The ``mustang`` device type can support both U-Boot and UEFI bootloaders but
  not on the same machine at the same time. The bootloader can be changed, but
  this is a custom process which is not manageable during a test job. In the
  Cambridge lab, ``mustang`` implies U-Boot and a separate sub device type
  called ``mustang-uefi`` is available for test jobs needing UEFI.

* ``panda`` devices can support operating systems like Debian as well
  as supporting Android deployments using the same bootloader in both
  cases (U-Boot). Therefore, only one device type was needed here.

.. _device_type_elements:

Database elements for a device type
===================================

The device type exists as a django database object which can be modified using
the :ref:`django admin interface<django_admin_interface>`. The following fields
are supported:

* **Name** - the name of the device type
  See :ref:`naming_device_types`. It is helpful to make the device type name
  similar to or the same as the name of the template file which will be
  extended by the device dictionary. The scheduler logs will use the database
  name, irrespective of what the device dictionaries extend. Use an ``alias``
  where the device type name differs from the template name(s) in use by
  devices of this type. (An Alias is one of the
  :ref:`device_type_descriptive_fields`.)

* **Health check job** - the YAML test job submission for a health check
  See :term:`health check`

* **Display** - should this device type be displayed in the GUI or not?
  Enabled by default - device type display can be disabled to hide the data
  about the device type from the UI, without deleting the object and
  associated data. The device type remains accessible in the django
  administrative interface.

* **Owners only** - device type is only visible to owners of devices of this type
  Disabled by default - enable to create a :term:`hidden device type`.

* **Health check frequency** - how often to run health checks
  Each device type can run health checks at a specified frequency which can be
  based on time intervals or numbers of test jobs.

.. _device_type_descriptive_fields:

Descriptive fields
------------------

The device type database also includes some optional fields which may be
completed by the admin to provide information for test writers:

* **Architecture name**
  e.g. ARMv7, ARMv8

* **Processor name**
  e.g. AM335X

* **Alias**
  A list of :term:`aliases <alias>` for this device type.
  e.g. 'am335x-boneblack'

* **CPU model name**
  e.g. OMAP 4430 / OMAP4460

* **List of cores**
  The number of cores on the device and the type of CPUs. In the admin
  interface, cores can be added and the number of each core specified. e.g. 4 x
  Cortex-A9

* **Bit count**
  e.g. 32 or 64

.. note:: When modifying device type objects in the
   :ref:`django_admin_interface`, take care with multiple selection boxes.
   Fields like architecture name or :term:`alias` can show in the list as being
   available for selection in a device type object but only the **selected**
   line or lines will actually be saved as references within the device type
   object. The references will show up on the device type detail page in the
   *Information* tab.
