Marek Vasut

OS kernel on embedded ARM64 systems requires PSCI interface to bring CPU cores up/down, suspend/resume/reset/power off. U-Boot bootloader provides a PSCI interface and this talk explains it.

The talk consists of five parts -- how the PSCI interface works, where and how OS kernel calls it, how and in which hooks on the bootloader side do those calls land, and how those hooks in U-Boot provide functionality required by OS. Last part is an example of U-Boot configured to provide PSCI interface on contemporary SoC .

The benefit of using the U-Boot PSCI interface over other PSCI interface providers is twofold. First, it allows for utilizing the full potential of U-Boot, and especially the SPL preloader, which can then boot OS kernel directly and quickly. Second, removing one software component from the boot stack reduces the Software BoM.

Prednaska pojedna o celem procesu oziveni embedded systemu, od hardwarove funkcniho prototypu zarizeni az po bootujici Linuxovy userspace. Prvni cast prednasky pokryva zavadec U-Boot, jak jej zkompilovat, jak do nej pridat nove zarizeni, device tree a driver model, jak jej spustit na desce pomoci JTAG debuggeru OpenOCD. Pro doplneni bude vysvetlen i TF-A. Druha cast se bude zabyvat Linuxovym jadrem, jak jej zkompilovat, pridat podporu HW, nabootovat ze site pomoci TFTP. Treti cast se bude venovat OpenEmbedded, predstavi jak jej vyuzit k sestaveni userspace a jak jej snadno otestovat pomoci bootu z NFS. Prednaska bude uzavrena posilanim patchu do upstreamu. Prednaska obsahuje prakticke ukazky z bringupu desky se STM32MP1.

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This presentation is a practical guide to implementing U-Boot bootloader port to a new system from scratch. At the beginning, two main pilars of contemporary U-Boot, device tree (DT) support and driver model (DM), are explained. This is followed by an in-depth look at the crucial subsystems, clock, pinmux, serial, block and a few other commonly used ones. Finally, systems with limited resources and multi-stage booting is discussed. The talk includes examples and experiences from platforms recently added to mainline U-Boot.

This presentation is a practical guide to implementing U-Boot port to a new system from scratch. U-Boot is the de-facto standard bootloader for embedded systems, there is plenty of U-Boot ports, yet vast majority of those are implemented in sub-optimal way. This talk first explains the U-Boot internals, the driver model (DM) and it's interaction with device tree (DT), as understanding these is vital to understanding the implementation of core subsystems. The core subsystems are explained in detail afterward to allow developers implement drivers the intended way without hacks and workarounds. Unfortunately, not all systems have plenty of resources, but U-Boot caters for those as well. The final part of the talk discusses the U-Boot SPL, the preloader which initializes the hardware, DRAM and starts U-Boot and finer parts of this procedure, which tends to have plenty of pitfalls.