linux-kernel - Re: [PATCH RFC 0/2] RISC-V: T-Head vector handling

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Message-ID: <mhng-ca852a2c-a1c7-4b14-a9a2-f2bd4541d6b7@palmer-ri-x1c9>
Date:   Mon, 12 Jun 2023 08:29:49 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     heiko@...ech.de, guoren@...nel.org
CC:     linux-riscv@...ts.infradead.org, samuel@...lland.org,
        christoph.muellner@...ll.eu, heiko@...ech.de,
        Conor Dooley <conor.dooley@...rochip.com>,
        linux-kernel@...r.kernel.org, heiko.stuebner@...ll.eu
Subject:     Re: [PATCH RFC 0/2] RISC-V: T-Head vector handling

On Tue, 14 Mar 2023 22:29:41 PDT (-0700), Palmer Dabbelt wrote:
> On Tue, 28 Feb 2023 13:54:33 PST (-0800), heiko@...ech.de wrote:
>> From: Heiko Stuebner <heiko.stuebner@...ll.eu>
>>
>> As is widely known the T-Head C9xx cores used for example in the
>> Allwinner D1 implement an older non-ratified variant of the vector spec.
>>
>> While userspace will probably have a lot more problems implementing
>> support for both, on the kernel side the needed changes are actually
>> somewhat small'ish and can be handled via alternatives somewhat nicely.
>>
>> With this patchset I could run the same userspace program (picked from
>> some riscv-vector-test repository) that does some vector additions on
>> both qemu and a d1-nezha board. On both platforms it ran sucessfully and
>> even produced the same results.
>>
>>
>> As can be seen in the todo list, there are 2 places where the changed
>> SR_VS location still needs to be handled in the next revision
>> (assembly + ALTERNATIVES + constants + probably stringify resulted in
>>  some grey hair so far already)
>>
>>
>> ToDo:
>> - follow along with the base vector patchset
>> - handle SR_VS access in _save_context and _secondary_start_sbi
>>
>>
>> Heiko Stuebner (2):
>>   RISC-V: define the elements of the VCSR vector CSR
>>   RISC-V: add T-Head vector errata handling
>>
>>  arch/riscv/Kconfig.erratas           |  13 +++
>>  arch/riscv/errata/thead/errata.c     |  32 ++++++
>>  arch/riscv/include/asm/csr.h         |  31 +++++-
>>  arch/riscv/include/asm/errata_list.h |  62 +++++++++++-
>>  arch/riscv/include/asm/vector.h      | 139 +++++++++++++++++++++++++--
>>  5 files changed, 261 insertions(+), 16 deletions(-)
>
> I have no opposition to calling the T-Head vector stuff an errata
> against V, the RISC-V folks have already made it quite apparent that
> anything goes here.  I would like to get the standard V uABI sorted out
> first, though, as there's still a lot of moving pieces there.  It's kind
> of hard here as T-Head got thrown under the bus, but I'm not sure what
> else to do about it.

The V-1.0 support has been merged, so I think we're good to go.  Does 
someone mind re-spinning this against for-next so it lines up with all 
the new user interfaces?