Embedded / Arch

http://tinyurl.com/yd5l4mak https://hackmd.io/CwdgnAxghgrAzAEwLQAYBMKBsTgEYFhJhgCmESUCAHGAEa0wBmtcIjQA#

RISC-V Update Slides

• GENERIC kernel added August 2017
• Updates for new Privileged Architecture (v1.10)
  • VM changes required to access userspace from supervisor (kernel)
  • Execute only pages not acceasable from kernel. Unclear if this matters (Brooks: execute-only isn't practical with normal compilers and modern languages)
• Testing with Compressed Extension (smaller instructions)
  • Compression ratio 1.19 vs 1.25 for micromips
• Finally migrated to FDT

• Work in progress on GENERIC kernel
• Discussion is ongoing to add armv7 as a TARGET_ARCH (andrew@ thinks likely)
  • LLD currently supports only armv7 for 32-bit arm

• andrew@ working NUMA support for dual package ThunderX
• Single package ThunderX and SoftIron work
• Raspberry-pi 3 works
• 64-bit pi2 not yet working due to firmware
• Most systems work with a GENERIC kernel
• ThunderX in the cluster to build packages
• ThunderX2 on the way, but completely different hardware so may need considerable work
• Ed started working on bringing up ODROID C2
• Would be useful to have a status chart listing what works on what platforms

• external toolchain with clang and lld mostly working
• hardfloat target arches added by br@, probalby need more testing and package builds
• Tests largely work, but some racey issues
• br@ tried micromips builds. Compilation works, but some work required on exception handlers.

• No users present

• No modern processors supported
• No modern clang support. Will need to test external GCC or remove.
• Unclear if a decent emulator exists. What is qemu status for sun4u? (MarkLinimon adds later: running qemu-sparc64 on amd64 merely hangs.)

• Switching to builtin clang or external GCC for all architectures
• Tier 1 likely to require in-tree premissively licensed toolchain
  • Still lacking a KLLDB
• Need to pick a toolchain file for targets with out of tree toolchains

• Need to do more if we're going to handle (e.g) MIPS 24k APs and netflix 100+Gbps per host systems
  • Don't want a zillion knobs
  • Perhaps big vs small
    • Maybe in per arch std.FOO files?
    • Consider default file of nooptions, nodevice for tiny systems
    • Warner's minimal kernel project may also help

• For RPi we would benefit from device tree overlays.
  • What is the status?
  • Need loader support?
• It would be nice if we had compatible python interfaces to our SPI, I2C, GPIO interfaces
  • Really does need to just work with existing examples
  • Ed reports that basic stuff does work
• Ed's coop student looking into adding FreeBSD to noobs (https://www.raspberrypi.org/downloads/noobs/)
  • Current RPi boot process makes it hard to integrate FreeBSD
  • Requires uboot changes to work well. In particular, need a way to tell uboot where it was loaded from.

• Work in progress on bhyve for arm and arm64, Andy is currently reviewing patches
• Power9 has extensions, but no easy way to access
• Most recent MIPS versions support, but no access to hardware currently

• Tier 1 and probably 2 should have QEMU