cf979fcf — Heinrich Schuchardt 7 months ago
u-boot-hooks: add virtio-rng-pci
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Add Contributing.md
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You can also use your local clone with git send-email.


This repository contains working example support ("hook") scripts for U-Boot's built-in test framework. That framework is located in the test/py/ directory in the U-Boot source tree.

You may use these examples as a reference when creating your own hook scripts, or even derive your own scripts directly from the files in this repository.


See Contributing.md.

#Flashing Philosophy

U-Boot may be installed onto a target device either by:

  • Writing the U-Boot binary to flash, so that it runs at every cold boot or reset. In this case, flashing is a one-time operation.

  • Downloading U-Boot into RAM whenever it needs to RAM. In this case, the download needs to happen every time the target board is reset, since the desired binary is not permanently stored on the system.

The example scripts in this repository take the second approach. This approach avoids modifying the device's flash memory for each U-Boot binary to be tested, which should increase longevity of the device. This does mean that the implementation of the test/py/ hook scripts is slightly inconsistent with their naming; u-boot-test-flash does nothing whereas u-boot-test-reset downloads U-Boot into RAM rather than only performing a simple system reset.

#USB Port Paths

When multiple USB devices of the same type are attached to the same system, some mechanism for differentiating between them is required, in order for software to choose which device to communicate with. In some cases, the only available mechanism is based on the physical USB port to which the device is attached. For this mechanism to work, there must be a stable way to uniquely name each physical USB port. The naming convention is known as the USB port path.

Each USB bus in the system is assigned a unique number by the Linux kernel. These numbers are typically stable across reboots since they are assigned based on device creation or probing order, which is usually driven by stable BIOS-driven data structures. Changes to system hardware can cause these numbers to change though. Equally, it's a good idea to validate the bus numbers after reboot. The USB bus number forms the first part of the USB port path.

Each USB controller or hub contains a number of physical USB ports (sockets). Each of these has a unique fixed number, per the USB specification. These port numbers form the balance of the USB port path.

Linux uses the format ${bus}-${port}.${port}.${port}... to represent the USB port path.

For example:

| PC           |
| +----------+ |
| | USB ctlr | |
| | Bus 4    | |       +----------+
| |   Port 1 |---------| USB hub  |
| +----------+ |       |   Port 1 |     +-----------------+
+--------------+       |   Port 2------ | USB device      |
                       |   Port 3 |     | Port path 4-1.2 |
                       +----------+     | Bus/device 4/15 |

Note that USB device numbers are not stable; they change each time a device appears on the bus, such as when it is power cycled or reset.

To determine the USB port path of your device, first manually identify a device node related to your USB device. For example, you might run lsusb with the device both unplugged and plugged in, find the device's bus and device number, and then use device file /dev/bus/usb/${busnum}/${devnum}. Alternatively, you may find some type-specific device node such as /dev/ttyUSB2 or /dev/sdc by experimentation using tools such as picocom or mount and ls.

Once a device node has been identified, use udevadm to query all known information about the device, then find an entry with SUBSYSTEMS=="usb" and a KERNELS value in the format of a USB port path:

$ udevadm info -a /dev/ttyUSB2
looking at device '/devices/pci0000:00/0000:00:14.0/usb3/3-6/3-6:1.2/ttyUSB2/tty/ttyUSB2':

looking at parent device '/devices/pci0000:00/0000:00:14.0/usb3/3-6/3-6:1.2/ttyUSB2':
looking at parent device '/devices/pci0000:00/0000:00:14.0/usb3/3-6/3-6:1.2':
looking at parent device '/devices/pci0000:00/0000:00:14.0/usb3/3-6':
looking at parent device '/devices/pci0000:00/0000:00:14.0/usb3':

Here, the USB port path is "3-6".


$ udevadm info -a /dev/bus/usb/003/086
looking at device '/devices/pci0000:00/0000:00:14.0/usb3/3-10/3-10.4':

Here, the USB port path is "3-10.4".

#udev Rules

See the udev/ directory in this repository.

Testing should be performed as a non-root user. This requires that the relevant device nodes have non-default permissions. udev rules may be used to achieve this.

To save hardware, it is possible to attach multiple Tegra devices to a single host machine. This requires that each program that interacts with the device be able to communicate with a specific Tegra device.

Some applications allow the USB port path be passed to them as a parameter. This requires no configuration via udev.

Some applications use device-specific properties to identify devices, such as the serial number encoded into a USB device descriptor. This requires no configuration via udev.

Other applications allow a USB device filename to be passed in. udev rules may be used to create well-known device filenames based on a device's USB port path.

The example udev rules demonstrate both of these types of rules.

#Scripts and Binaries

See the bin/ directory in this repository.

Scripts exist to power on, power off, flash, and reset Tegra boards, and access their serial console. The U-Boot test framework expects these scripts to exist in $PATH, and executes them at appropriate times.

Note that the test framework itself does not use the power on/off scripts. However, they may be used by a companion continuous integration framework that triggers the U-Boot test framework. For example, https://github.com/swarren/u-boot-ci-scripts.

U-Boot's test framework identifies each board by type (e.g. p2371-2180; the engineering name for Jetson TX1) and identity (an arbitrary user-assigned string used to differentiate multiple instances of the same board type within a user's testing setup). Each script is passed these two parameters to inform it which board to operate upon.

Different test setups will use different techniques to control target hardware. For example, reset and forced recovery signals may be manipulated through NVIDIA's proprietary PM342 debug board, or some form of relay or electronic switch board hard-wired to the board's physical buttons.

The scripts are written to be highly generic, and allow sharing of code between boards. To this end, the top-level implementation of each script does little more than include a board-specific configuration file, and then include another file specific to implementation the desired action.

Board configuration files are located in bin/${hostname}/conf.${board_type}_${board_identity}. These files are segregated by hostname so that the repository can be used directly across multiple different test machines, without the need for host-specific branches or post-checkout configuration.

The board configuration file defines which mechanism is used for each possible action, and any parameters associated with it. For example, downloading U-Boot into RAM may used either the tegra-uboot-flasher tool for boards containing T124 or earlier, or L4T's exec-uboot.sh for boards containing T210 or newer. These scripts. In each case, the directory name where the tool is installed must be defined.

Each action is implemented in a script fragment directly in the bin/ directory, with filename ${action_type}.${implementation_name}.

If using these scripts directly for testing Tegra devices, it is likely that you will not need to create new download.* implementations, but will need to create new poweroff.*, poweron.*, and recovery.* implementations.

Observe that some external tools (download.* especially) invoked by these scripts must be replicated once per board instance, or their actions somehow serialized, since they copy files into their own directories when executing, and hence parallel execution would cause incorrect operation.


The example scripts depend on various external tools, the installation location of which must be specified in the board configuration files:

U-Boot's test framework also requires a dfu-util that supports the -p command-line option. Most distros provide this nowadays.

#Python Modules

See the py/ directory in this repository.

A Python module exists for each board and defines numerous parameters used by the U-Boot test framework. The framework expects to simply import these modules directly, and hence they must be locatable within $PYTHONPATH.

These modules are again located in a separate directory for each host, so that the repository may be shared across hosts.

For complete details re: the required content of these Python modules, please see test/py/README.md in the U-boot source tree, and also the comments in some individual test files in test/py/tests/test_*.py.