Geert Uytterhoeven

Virtualization, including safe pass-through guest access to devices, is a well-known and mature technology on servers. With the increasing complexity and abilities of SoCs, virtualization is gaining importance on embedded systems, too. In this presentation, Geert will explore virtualization and device pass-through (VFIO) using QEMU and KVM on a Device Tree-based embedded ARM system, pursuing the holy grail of embedded developers: the ability to blink a connected LED. While seemingly too trivial and inapplicable, Geert will show how relevant such a contrived example is to more complex real-world uses of device pass-through. He will talk about the obstacles he encountered, and how they were overcome, enabling the use of device pass-through for real on-SoC devices using DMA. Finally, Geert will discuss when to use device pass-through, and when other virtualization techniques offer a better solution.

In this presentation, embedded developers will get a grasp of virtualization, and can expect a hands-on report of getting device pass-through working on DT-based systems, enabling them to accelerate implementing virtualization in their own projects and products. Understanding the differences between traditional PCI-based servers, and relatively new embedded systems with DT, will help software developers improve support for device pass-through, in both Linux and virtualization environments like QEMU/KVM. Hardware (SoC and board) designers will learn about the impact of their design decisions on virtualization, and what to take into account to allow efficient virtualization of hardware devices.

The SPI bus connects a master with one or more slave devices. So far, Linux always assumed the master role. In v4.13, Linux finally gained slave support. In this presentation, Geert will talk about adding SPI slave mode support to the existing SPI subsystem, and using a Linux system as an SPI slave. He will show what makes SPI special, and cover possible use cases and limitations of Linux-based SPI slave mode. Finally he will demonstrate how he modified Linux to add support for SPI slave mode.

The SPI (Serial Peripheral Interface) bus is ubiquitous in many (embedded) systems. Devices connected to an SPI bus have master and slave roles. Traditionally, the Linux kernel always assumed the SPI master role. In v3.19, Linux received i2c slave support. This sparked the question if Linux could ever become an SPI slave, controlled by an external SPI master, too. In v4.13, that question was finally answered with a "yes"; but not wholeheartedly. In this presentation, Geert will talk about adding SPI slave mode support to the existing SPI subsystem, and using a Linux system as an SPI slave. This can increase the roles and functionalities Linux can perform in embedded systems. Attendees can expect an overview of the SPI bus and the differences between SPI master and slave roles, and a comparison with other simple buses. They will understand the challenges of using Linux as an SPI slave, and can consider the implications when designing SPI protocols for use with Linux systems acting as an SPI slave. They will learn how to write SPI slave handlers for Linux, implementing the slave-side of an SPI protocol.