The Role of Open Source Firmware in RISC-V Atish Patra <[email protected]> Alistair Francis <[email protected]> Anup Patel <[email protected]> OSFC – 3rd of September 2019 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 Outline •Introduction to RISC-V •Industry standard Open source bootloaders •Current RISC-V boot flow •OpenSBI Project •Upstream Status •Future work •Demo © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 2 Acknowledgements •U-Boot – Lukas Auler – Bin Meng – Anup Patel •Coreboot – Ron Minnich – Patrick Rudolph – Shawn Chang •EDK2 – Abner Chang • And others © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 3 What is RISC-V? •Pronounced as risk-five •An open RISC Instruction Set Architecture (ISA) •The base ISA is incredibly small – The ISA can be extended • Integer (I) and Embedded (E) are part of the base ISA • Multiply/Divide (M), Atomic (A), Single Floating Point (F), Double Floating Point (D), Quad Floating Point (Q) and Compressed Instructions (C) are frozen already • Virtualisation (H), Vector (V), Bit Manipulation (B) are examples of draft extensions • The General Extension (G) is shorthand for M, A, F and D – Aimed at everything from small embedded systems to high end HPC •Multiple CPU implementations already available •SiFive, BOOM, Rocket64, Andes, QEMU, etc •Currently heavily backed by SiFive, Microsemi, NVIDIA, Western Digital and others © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 4 Why RISC-V? •An open source ISA allows anyone to use and modify the ISA without any licensing cost – This is different to commercial companies which ship black boxes with strict NDAs •Customization for specific applications •Security audits to verify security in critical applications •Lower cost users (such as small companies or hobbyists) to use the ISA •Community driven development approach allows input from anybody – The RISC-V foundation still decides on the final specifications © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 5 Industry standard boot loaders • Runs from DDR Proprietary • Typically open-source • DDR initialization • Filesystem support Open • Loads RUNTIME and • Network booting Source BOOTLOADER • Boot configuration • Examples: • Examples: • BIOS/UEFI • U-Boot Loads • U-Boot SPL • GRUB • Coreboot ROM stage • LinuxBoot Jumps ROM LOADER RUNTIME BOOTLOADER OS • Runs from On-Chip • Runs from On-Chip SRAM or ROM DDR • Uses On-Chip SRAM • SOC security setup • SOC power-up and • Runtime services as-per clock setup specifications • Examples: • ATF • BIOS/UEFI © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 6 RISC-V Upstream Boot Flow Follows commonly used multiple boot stages model Proprietary Open Loads Source RISC-V Jumps specific ZSBL FSBL OpenSBI U-Boot Linux (M-mode) (M-mode) (M-mode) (S-mode) (S-mode) (ROM) (LOADER) (RUNTIME) (BOOTLOADER) (OS) • Follows a standard boot flow • Uses U-Boot as the last stage boot loader • U-Boot binary as the payload to OpenSBI • FSBL is SiFive specific and will be replaced by Coreboot/U-Boot SPL • OpenSBI is a RISC-V specific runtime service provider © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 7 What is SBI ? •SBI is the RISC-V Supervisor Binary Interface – System call style calling convention between Supervisor (S-mode OS) and Supervisor Execution Environment (SEE) •SEE can be: App1 App2 – A M-mode RUNTIME firmware for OS/Hypervisor running in HS-mode ABI ABI – A HS-mode Hypervisor for Guest OS running in VS-mode OS (S-Mode) SBI •SBI calls help: SEE (M-Mode) – Reduce duplicate platform code across OSes (Linux, FreeBSD, etc) – Provide common drivers for an OS which can be shared by multiple platforms – Provide an interface for direct access to hardware resources (M-mode only resources) •Specifications being drafted by the Unix Platform Specification Working group – Maintain and evolve the SBI specifications – Currently, SBI v0.1 in-use and SBI v0.2 in draft stage © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 8 What is OpenSBI ? •OpenSBI is an open-source implementation of the RISC-V Supervisor Binary Interface (SBI) specifications – Licensed under the terms of the BSD-2 clause license – Helps to avoid SBI implementation fragmentation – Maintained by the community •Aimed at providing RUNTIME services in M-mode – Typically used in boot stage following ROM/LOADER •Provides support for reference platforms – Generic simple drivers included for M-mode to operate ▪ PLIC, CLINT, UART 8250 – Other platforms can reuse the common code and add needed drivers © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 9 Key Features •Layered structure to accommodate various use cases – Generic SBI library with platform abstraction • Typically used with external firmware and bootloader OpenSBI Layers – EDK2 (UEFI implementation), Secure boot working group – Platform specific library Platform Specific Reference Firmware • Similar to core library but including platform specific drivers – Platform specific reference firmware Platform Specific • Three different types of RUNTIME firmware Library •Wide range of hardware features supported SBI Library – RV32 and RV64 – Misaligned load/store handling – Missing CSR emulation – Protects firmware using PMP support © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 10 Reference Firmwares •OpenSBI provides several types of reference firmware, all platform-specific – FW_PAYLOAD • Firmware with the next booting stage as a payload • Default firmware being used in Linux capable RISC-V hardware – FW_JUMP • Firmware with static jump address to the next booting stage • Default method for QEMU – FW_DYNAMIC • Firmware with dynamic information on the next booting stage • U-Boot SPL is using FW_DYNAMIC •SOC Vendors may choose: – Use one of OpenSBI reference firmwares as their M-mode RUNTIME firmware – Build M-mode RUNTIME firmware from scratch with OpenSBI as library – Extend existing M-mode firmwares (U-Boot_M_mode/EDK2) with OpenSBI as library © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 11 Platform support •SiFive HiFive Unleashed •Andes AE350 •Ariane FPGA SOC •Kendryte K210 •QEMU virt machines (32-bit/64-bit) © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 12 Upstream status Rapid progress: traditional full boot support expected by year end •OpenSBI •Grub – Actively developed and maintained – RISC-V support available upstream – Version 0.4 released •Linux Kernel – Default in Buildroot, Yocto/OpenEmbedded and – Upstream kernel boots in QEMU the QEMU “BIOS” – 5.3 kernel works with OpenSBI+U-Boot – Fedora/Debian provides images available with OpenSBI binary on HiFive Unleashed •U-Boot – U-Boot-2019.07 release has HiFive Unleashed S-mode support with SMP – Boot via network supported – MMC boot support coming in 2019.10 – EFI support for RISC-V available © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 13 Planned boot flow using U-Boot SPL •OpenSBI firmware with dynamic information about the next booting stage •Coreboot support available on both hardware & QEMU •U-Boot SPL Only available for QEMU for now •HiFive Unleashed U-Boot SPL support not available yet Proprietary Open Loads Source RISC-V Passed via ‘a2’ register Jumps specific ZSBL U-Boot SPL struct OpenSBI U-Boot Linux (M-mode) Coreboot fw_dynamic_info (M-mode) (S-mode) (S-mode) (ROM) (M-mode) (RUNTIME) (BOOTLOADER) (OS) © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 14 Planned boot flow using EDK2 •Work in progress •Open Source EDK2 (UEFI implementation) OpenSBI integration – HPE leading this effort – Available in EDK2 mailing list for U540 on Xilinx VC707 FPGA – OpenSBI built with EDK2 build environment •OpenSBI used as library in Pre-EFI Initialization (PEI) Phase •Driver eXecution Environment (DXE) Phase in S-mode will use OpenSBI function wrappers to make ecalls (Not done yet) © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 15 Future boot support Toward a stable and easy to use boot ecosystem •EFI stub support in Linux kernel for full UEFI support – Enterprise class boot environment •U-Boot SPL support for hardware •Booting from SDCARD in coreboot possible ? •EDK2 project upstreaming •LinuxBoot ? •Other bootloaders ? © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 16 Ongoing work Toward a stable and easy to use boot ecosystem •SBI specifications – SBI v0.2 specification – Power management extension in SBI •OpenSBI – SBI v0.2 support – Sequential cpu boot via CPU hotplug – Support other M-mode boot loader such as Coreboot/U-Boot SPL – Hypervisor support – More platforms support • Need hardware ! © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 17 OSTree •OSTree can be thought of as git for operating system updates •It is used to mange Linux system operating system updates •Unlike git OSTree “checks out” files using hardlinks, so the rootFS is immutable to prevent corruption •OSTree started with Gnome Continuous (high performance continuous delivery/testing system for GNOME) •OSTree is used in meta-updater (an OE layer) and Fedora SilverBlue •Flatpak uses libostree © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 18 Demo 1: U-Boot TFTP boot and OSTree © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 19 Demo 2: U-Boot MMC boot and OSTree © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 20 Thank you!! •Q&A ? © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 21 © 2019 Western Digital Corporation or its affiliates. All rights reserved. 8/30/19 Constraints on using OpenSBI Library •Same GCC target options (i.e. -march, -mabi, and -mcmodel) need to be used for the external firmware and OpenSBI sources •External firmware must create per-HART non-overlapping: 1.