On 11/14/24 11:02, Charlie Jenkins wrote:
On Thu, Nov 14, 2024 at 10:44:37AM +0800, Yangyu Chen wrote:
On 11/14/24 10:21, Charlie Jenkins wrote:
Add a new hwprobe key "RISCV_HWPROBE_KEY_VENDOR_EXT_THEAD_0" which
allows userspace to probe for the new RISCV_ISA_VENDOR_EXT_XTHEADVECTOR
vendor extension.
Hi Charlie,
How about changing the name of the key from
"RISCV_ISA_VENDOR_EXT_XTHEADVECTOR" to "RISCV_HWPROBE_KEY_VENDOR_EXT_0" and
use marchid to identify what the vendor is, each vendor will have its own
bit definition in this value. So we can avoid adding so many hwprobe keys
for each vendor in the future.
I proposed a commit here: https://github.com/cyyself/linux/commit/36390645d85d1ac75dd71172f167719df4297f59
I actually originally had this in one of my first versions of this
series but was convinced by Conor to change it. The problem with it was
that tying vendor extensions to mvendorid means that it is enforced by
the kernel that vendors cannot share vendor extensions. It is possible
for vendor A to purchase IP that contains a vendor extension from vendor
B. This vendor extension should work on platforms created by vendor A
and vendor B. However, vendor A and vendor B have different mvendorids,
so the kernel can't support this if it is tied to mvendorid. It could
be solved by duplicating every extension that vendors have, but then
userspace software would have to keep in mind the mvendorid they are
running on and check the different extensions for the different vendors
even though the implementation of the extension is the same.
The original conversation where Conor and I agreed that it was better to
have vendor extensions not rely on mvendorid:
https://lore.kernel.org/linux-riscv/20240416-husband-flavored-96c1dad58b6e@wendy/
Thanks for your explanation. I will strongly agree with Conor's opinion
if the feature bitmask does not exist in RISC-V C-ABI.
However, as the feature mask defined in RISC-V C-ABI[1] uses the design
depending on marchid currently, should we reconsider this key for its
use case? The current target_clones and taget_version implemented in
GCC[2] and LLVM[3] also use the bitmask defined in C-ABI. I think if we
use this key depending on marchid, to make a key shared with all vendors
will make this cleaner.
[1]
https://github.com/riscv-non-isa/riscv-c-api-doc/blob/main/src/c-api.adoc#function-multi-version
[2]
https://github.com/gcc-mirror/gcc/blob/8564d0948c72df0a66d7eb47e15c6ab43e9b25ce/gcc/config/riscv/riscv.cc#L13016
[3]
https://github.com/llvm/llvm-project/blob/f407dff50cdcbcfee9dd92397d3792627c3ac708/clang/lib/CodeGen/CGBuiltin.cpp#L14627
This new key will allow userspace code to probe for which thead vendor
extensions are supported. This API is modeled to be consistent with
RISCV_HWPROBE_KEY_IMA_EXT_0. The bitmask returned will have each bit
corresponding to a supported thead vendor extension of the cpumask set.
Just like RISCV_HWPROBE_KEY_IMA_EXT_0, this allows a userspace program
to determine all of the supported thead vendor extensions in one call.
Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
Reviewed-by: Evan Green <evan@xxxxxxxxxxxx>
---
arch/riscv/include/asm/hwprobe.h | 3 +-
.../include/asm/vendor_extensions/thead_hwprobe.h | 19 +++++++++++
.../include/asm/vendor_extensions/vendor_hwprobe.h | 37 ++++++++++++++++++++++
arch/riscv/include/uapi/asm/hwprobe.h | 3 +-
arch/riscv/include/uapi/asm/vendor/thead.h | 3 ++
arch/riscv/kernel/sys_hwprobe.c | 5 +++
arch/riscv/kernel/vendor_extensions/Makefile | 1 +
.../riscv/kernel/vendor_extensions/thead_hwprobe.c | 19 +++++++++++
8 files changed, 88 insertions(+), 2 deletions(-)
