[PATCH 00/19] riscv: Support vendor extensions and xtheadvector

Charlie Jenkins
2024-04-12T04:11:53Z

This patch series ended up much larger than expected, please bear with
me! The goal here is to support vendor extensions, starting at probing
the device tree and ending with reporting to userspace.

The main design objective was to allow vendors to operate independently
of each other. This has been achieved by delegating vendor extensions to
a new struct "hart_isa_vendor" which is a counterpart to "hart_isa".

Each vendor will have their own list of extensions they support. Each
vendor will have a "namespace" to themselves which is set at the key
values of 0x8000 - 0x8080. It is up to the vendor's disgression how they
wish to allocate keys in the range for their vendor extensions.

Reporting to userspace follows a similar story, leveraging the hwprobe
syscall. There is a new hwprobe key RISCV_HWPROBE_KEY_VENDOR_EXT_0 that
is used to request supported vendor extensions. The vendor extension
keys are disambiguated by the vendor associated with the cpumask passed
into hwprobe. The entire 64-bit key space is available to each vendor.

On to the xtheadvector specific code. xtheadvector is a custom extension
that is based upon riscv vector version 0.7.1 [1]. All of the vector
routines have been modified to support this alternative vector version
based upon whether xtheadvector was determined to be supported at boot.
I have tested this with an Allwinner Nezha board. I ran into issues
booting the board on 6.9-rc1 so I applied these patches to 6.8. There
are a couple of minor merge conflicts that do arrise when doing that, so
please let me know if you have been able to boot this board with a 6.9
kernel. I used SkiffOS [2] to manage building the image, but upgraded
the U-Boot version to Samuel Holland's more up-to-date version [3] and
changed out the device tree used by U-Boot with the device trees that
are present in upstream linux and this series. Thank you Samuel for all
of the work you did to make this task possible.

To test the integration, I used the riscv vector kselftests. I modified
the test cases to be able to more easily extend them, and then added a
xtheadvector target that works by calling hwprobe and swapping out the
vector asm if needed.

[1] https://github.com/T-head-Semi/thead-extension-spec/blob/95358cb2cca9489361c61d335e03d3134b14133f/xtheadvector.adoc
[2] https://github.com/skiffos/SkiffOS/tree/master/configs/allwinner/nezha
[3] https://github.com/smaeul/u-boot/commit/2e89b706f5c956a70c989cd31665f1429e9a0b48

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
---
Charlie Jenkins (18):
dt-bindings: riscv: Add vendorid and archid
riscv: cpufeature: Fix thead vector hwcap removal
dt-bindings: riscv: Add xtheadvector ISA extension description
riscv: dts: allwinner: Add xtheadvector to the D1/D1s devicetree
riscv: Fix extension subset checking
riscv: Extend cpufeature.c to detect vendor extensions
riscv: Optimize riscv_cpu_isa_extension_(un)likely()
riscv: Introduce vendor variants of extension helpers
riscv: uaccess: Add alternative for xtheadvector uaccess
riscv: csr: Add CSR encodings for VCSR_VXRM/VCSR_VXSAT
riscv: Create xtheadvector file
riscv: vector: Support xtheadvector save/restore
riscv: hwprobe: Disambiguate vector and xtheadvector in hwprobe
riscv: hwcap: Add v to hwcap if xtheadvector enabled
riscv: hwprobe: Add vendor extension probing
riscv: hwprobe: Document vendor extensions and xtheadvector extension
selftests: riscv: Fix vector tests
selftests: riscv: Support xtheadvector in vector tests

Heiko Stuebner (1):
RISC-V: define the elements of the VCSR vector CSR

Documentation/arch/riscv/hwprobe.rst | 12 +
Documentation/devicetree/bindings/riscv/cpus.yaml | 11 +
.../devicetree/bindings/riscv/extensions.yaml | 9 +
arch/riscv/boot/dts/allwinner/sun20i-d1s.dtsi | 4 +-
arch/riscv/include/asm/cpufeature.h | 143 +++++++---
arch/riscv/include/asm/csr.h | 13 +
arch/riscv/include/asm/hwcap.h | 23 ++
arch/riscv/include/asm/hwprobe.h | 4 +-
arch/riscv/include/asm/sbi.h | 2 +
arch/riscv/include/asm/vector.h | 228 ++++++++++++----
arch/riscv/include/asm/xtheadvector.h | 25 ++
arch/riscv/include/uapi/asm/hwprobe.h | 10 +-
arch/riscv/kernel/cpu.c | 20 ++
arch/riscv/kernel/cpufeature.c | 264 +++++++++++++++---
arch/riscv/kernel/kernel_mode_vector.c | 4 +-
arch/riscv/kernel/sys_hwprobe.c | 59 ++++-
arch/riscv/kernel/vector.c | 22 +-
arch/riscv/lib/uaccess.S | 1 +
tools/testing/selftests/riscv/vector/.gitignore | 3 +-
tools/testing/selftests/riscv/vector/Makefile | 17 +-
.../selftests/riscv/vector/v_exec_initval_nolibc.c | 93 +++++++
tools/testing/selftests/riscv/vector/v_helpers.c | 66 +++++
tools/testing/selftests/riscv/vector/v_helpers.h | 7 +
tools/testing/selftests/riscv/vector/v_initval.c | 22 ++
.../selftests/riscv/vector/v_initval_nolibc.c | 68 -----
.../selftests/riscv/vector/vstate_exec_nolibc.c | 20 +-
.../testing/selftests/riscv/vector/vstate_prctl.c | 295 ++++++++++++---------
27 files changed, 1114 insertions(+), 331 deletions(-)
---
base-commit: 4cece764965020c22cff7665b18a012006359095
change-id: 20240411-dev-charlie-support_thead_vector_6_9-1591fc2a431d
--
- Charlie