Technical – Bootlin

LTP: Linux Test Project, Bootlin contributions

Introduction

The Linux Test Project is a project that develops and maintains a large test suite that helps validating the reliability, robustness and stability of the Linux kernel and related features. LTP has been mainly developed by companies such as IBM, Cisco, Fujitsu, SUSE, RedHat, with a focus on desktop distributions.

On the embedded side, both the openembedded-core Yocto layer and Buildroot have packages that allow to use LTP on embedded targets. However, for a recent project, we practically tried to run the full LTP test suite on an i.MX8 based platform running a Linux system built with Yocto. It turned out that LTP was apparently not very often tested on Busybox-based embedded systems, and we faced a number of issues. In addition to reporting various bugs/issues to the upstream LTP project, we also contributed a number of fixes and improvements:

Our contributions received a very warm welcome in the LTP community, which turned out to be very open and responsive. We hope that these contributions will encourage others to use LTP, and hopefully to make sure it continues to work on embedded platforms.

Quick start guide

At the time of this writing, LTP has more than 3800 tests written by the community, including about 1000 network-related tests. The tests are grouped together in categories described by files in the runtest/ folder. Based on this, two scenarios of tests are defined: default and network which are described by two files in the scenario_groups/ folder. These two scenarios simply list the categories of tests that need to be executed.

Here are the contents of the default and network:

$ cat scenario_groups/default 
syscalls
fs
fs_perms_simple
fsx
dio
io
mm
ipc
sched
math
nptl
pty
containers
fs_bind
controllers
filecaps
cap_bounds
fcntl-locktests
connectors
power_management_tests
hugetlb
commands
hyperthreading
can
cpuhotplug
net.ipv6_lib
input
cve
crypto
kernel_misc
uevent

$ cat scenario_groups/network 
can
net.features
net.ipv6
net.ipv6_lib
net.tcp_cmds
net.multicast
net.rpc
net.nfs
net.rpc_tests
net.tirpc_tests
net.sctp
net_stress.appl
net_stress.broken_ip
net_stress.interface
net_stress.ipsec_dccp
net_stress.ipsec_icmp
net_stress.ipsec_sctp
net_stress.ipsec_tcp
net_stress.ipsec_udp
net_stress.multicast
net_stress.route

Once you have LTP built and installed on your board thanks to the appropriate OpenEmbedded or Buildroot package, you can run these two scenarios of test with the following commands (-n specify the network one):

$ cd /opt/ltp
$ ./runltp
$ ./runltp -n

Then take a look at the content of the result and the output directories.

For more information on building or running LTP please read this readme.

Bootlin welcomes Hervé Codina in its team

Since March 1st, 2021, we’re happy to have an additional engineer, Hervé Codina, in our engineering team based in Toulouse, France.

Hervé has 20 years’ experience working in embedded systems, both bare-metal systems and embedded Linux systems, in a wide range of applications. Hervé has experience working with U-Boot, Barebox, Linux, Buildroot, Yocto, on ARM platforms from various silicon vendors. Hervé will work within our engineering team to deliver ready-to-use Linux Board Support Packages, port bootloaders and the Linux kernel to new platforms, develop Linux kernel device drivers, implement custom Linux systems with Buildroot or Yocto, and more. His 20 years experience will further increase the expertise that Bootlin provides to its worldwide customers.

See Hervé’s page on our site for more details. Hervé is joining our team in Toulouse, who already included Paul Kocialkowski, Miquèl Raynal, Köry Maincent, Maxime Chevallier, Thomas Perrot and Thomas Petazzoni.

Bootlin contributions to Linux 5.11

Linux 5.11 was released quite some time ago now, but it’s never too late to have a look at Bootlin contributions to this release. As usual, we recommend reading the LWN articles on the 5.11 merge window: part 1 and part2. Also of interest is the Kernelnewbies page for 5.11.

Here are the main highlights of our contributions:

Alexandre Belloni, as the maintainer of the RTC subsystem, continued making numerous improvements and fixes to RTC drivers
On the support for Microchip ARM platforms, Alexandre Belloni switched the PWM atmel-tcb driver to a new Device Tree binding and added SAMA5D2 support, he did some improvements to the IIO driver for the Microchip ADC, and continued to remove platform_data support from Microchip drivers as all platforms are now converted to the Device Tree.
Alexandre Belloni contributed a new Simple Audio Mux driver for the ALSA subsystem, which can be used to control simple audio multiplexers driven using GPIOs, that allows to select which of their input line is connected to the output line.
Grégory Clement added support for several new MIPS platforms from Microchip: Luton, Serval and Jaguar2. All those platforms include a MIPS core, a few peripherals and more importantly an Ethernet switch. For now the support only includes the base platform support, but we are working on the switchdev driver for the Ethernet switch.
Miquèl Raynal, maintainer of the NAND subsystem and co-maintainer of the MTD subsystem, contributed numerous changes to the ECC support in the MTD subsystem, making it more generic so that it can be used not just for parallel NAND flashes, but also SPI NAND flashes. For more details, see the talk from Miquèl Raynal on this topic.

In addition to those 95 patches that we authored and contributed, several Bootlin engineers being maintainers of different subsystems of the Linux kernel reviewed and merged patches from other contributors:

Miquèl Raynal, as the NAND maintainer and MTD co-maintainer, reviewed and merged 67 patches from other contributors
Alexandre Belloni, as the RTC, I3C and Microchip ARM/MIPS platforms maintainer, reviewed and merged 47 patches from other contributors
Grégory Clement, as the Marvell EBU platform co-maintainer, reviewed and merged 33 patches from other contributors

Here is the detailed list of our contributions to Linux 5.11:

Videos and slides of Bootlin presentations at FOSDEM 2021

The videos from Bootlin’s presentations earlier this month at FOSDEM 2021 are now publicly available. Once again, FOSDEM was a busy event, even if it was online for once. As in most technical conferences, Bootlin engineers volunteered to share their experience and research by giving two talks.

Maxime Chevallier – Network Performance in the Linux Kernel, Getting the most out of the Hardware

Abstract: The networking stack is one of the most complex and optimized subsystems in the Linux kernel, and for a good reason. Between the wild range of applications, the complexity and variety of the networking hardware, getting good performance while keeping the stack easily usable from userspace has been a long-standing challenge.

Nowadays, complex Network Interface Controllers (NICs) can be found even on small embedded systems, bringing powerful features that were previously found only in the server world closest to day to day users.

This is a good opportunity to dive into the Linux Networking stack, to discover what is used to make networking as fast as possible, both by using all the features of the hardware and by implementing some clever software tricks.

In this talk, we cover these various techniques, ranging from simple batch processing with NAPI, queue management with RSS, RPS, XPS and so on, flow steering and filtering with ethool and TC, to finish with the newest big change that is XDP.

We dive into these various techniques and see how to configure them to squeeze the most out of your hardware, and discover that what was previously in the realm of datacenters and huge computers can now also be applied to embedded linux development.

Here are PDF slides for this presentation.

Michael Opdenacker – Embedded Linux from Scratch in 45 minutes, on RISC-V

Abstract: Discover how to build your own embedded Linux system completely from scratch. In this presentation and tutorial, we show how to build a custom toolchain (Buildroot), bootloader (opensbi / U-Boot) and kernel (Linux), that one can run on a system with the new RISV-V open Instruction Set Architecture emulated by QEMU. We also show how one can build a minimal root filesystem by oneself thanks to the BusyBox project. The presentation ends by showing how to control the system remotely through a tiny webserver. The approach is to provide only the files that are strictly necessary. That’s all the interest of embedded Linux: one can really control and understand everything that runs on the system, and see how simple the system can be. That’s much easier than trying to understand how a GNU/Linux system works from a distribution as complex as Debian!

The presentation also shares details about what’s specific to the RISC-V architecture, in particular about the various stages of the boot process. This presentation shares all the hardware (!), source code build instructions and demo binaries needed to reproduce everything at home, and add specific improvements. Most of the details are also useful to people using other hardware architectures (in particular arm and arm64).

It’s probably the first time a tutorial manages to show so many aspects of embedded Linux in less than an hour. See by yourself! At least, that’s for sure the first one demonstrating how to boot Linux from U-Boot in a RISC-V system emulated by QEMU.

Here are PDF slides for this presentation.

Device Tree 101 webinar slides and videos

As we announced back in January, we have offered in partnership with ST on February 9 a free webinar titled Device Tree 101, which gives a detailed introduction to the Device Tree, an important mechanism used in the embedded Linux ecosystem to describe hardware platforms. We were happy to see the interest around this topic and webinar.

Bootlin has always shared freely and openly all its technical contents, including our training materials, and this webinar is no exception. We are therefore sharing the slides and video recording of both sessions of this webinar:

Thanks to everyone who participated and thanks to ST for the support in organizing this event! Do not hesitate to share and/or like our video, and to suggest us other topics that would be useful to cover in future webinars!