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 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.

      See also

      Device sub-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 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 talk to us.

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 device tag to describe small differences between devices of the same device type where it makes sense.

See also

Information tab.

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.

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.

Matching the template

The name of a device type does not need to match an available template, however the 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 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.

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.

Database elements for a device type

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

  • Name - the name of the device type See Choosing a name for a device type. 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 Descriptive fields.)
  • Health check job - the YAML test job submission for a health check See 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 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.

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 aliases 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 Django administration interface, take care with multiple selection boxes. Fields like architecture name or 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.