linux-kernel - Re: [PATCH] RISC-V: cpu.c: remove nonexistent ext from cpuinfo

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Message-ID: <mhng-7b349805-02ff-47b3-b9b5-31dcbd2bb256@palmer-ri-x1c9>
Date:   Wed, 01 Jun 2022 20:52:42 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...osinc.com>
To:     i@...ithal.me, i@...ithal.me, Kito Cheng <kito.cheng@...il.com>,
        Nelson Chu <nelson.chu@...ive.com>
CC:     Atish Patra <atishp@...osinc.com>, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject:     Re: [PATCH] RISC-V: cpu.c: remove nonexistent ext from cpuinfo

On Wed, 18 May 2022 01:40:18 PDT (-0700), i@...ithal.me wrote:
> On Tue, Apr 26, 2022 at 06:08:01AM +0800, Hongren (Zenithal) Zheng wrote:
>> There are no single-letter B/K/J extentions,
>> as they are never ratified. For P, it is still in
>> progress and not ratified.
>>
>> The ordering constraint of these placerholders is now removed
>> from the spec. By commit ("Delete more nonexistent
>> extensions from the naming constraints") of riscv/riscv-isa-manual
>
> Hi, is there any further update on this patch?

IIRC there was some debate as to whether that change constituted an 
incompatible change to the spec, but I guess it's stuck around for long 
enough that maybe we should count on it being canon now?  I added Kito 
and Nelson, there's a GNU toolchain call tomorrow morning so hopefully 
we can remember to talk about it...

>
>>
>> Signed-off-by: Hongren (Zenithal) Zheng <i@...ithal.me>
>> ---
>>  arch/riscv/kernel/cpu.c | 4 +---
>>  1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
>> index ccb617791e56..53a061ab0743 100644
>> --- a/arch/riscv/kernel/cpu.c
>> +++ b/arch/riscv/kernel/cpu.c
>> @@ -113,10 +113,8 @@ static void print_isa_ext(struct seq_file *f)
>>  /*
>>   * These are the only valid base (single letter) ISA extensions as per the spec.
>>   * It also specifies the canonical order in which it appears in the spec.
>> - * Some of the extension may just be a place holder for now (B, K, P, J).
>> - * This should be updated once corresponding extensions are ratified.
>>   */
>> -static const char base_riscv_exts[13] = "imafdqcbkjpvh";
>> +static const char base_riscv_exts[9] = "imafdqcvh";
>
> The base_riscv_exts "imafdqcvh" is exactly the spec now, as
> https://github.com/riscv/riscv-isa-manual/commit/db7a4a0dad0e99d1ec1fc67b582624fc0aeae98e
> (Add single-letter "H" extension to the table)
> has shown

Oddly enough I stumbled upon that one this morning, it's another one of 
these like the HPM stuff: we used to say "there's no letter describing 
the hypervisor behavior, so it's part of the base" (see the commentary 
on the binutils patch), but now that there's a letter I'm assuming we 
should split that out?

Not clear if the RISC-V folks want H to be ignored by software like 
those other recent changes, and if so it's also not clear that's a good 
idea.

Anyway, sorry this is taking a while but I think it's going to be too 
late for this merge window -- kind of silly for such a small patch, but 
it's got interface implications and it's all a bit of a hot topic right 
now.

>
>>
>>  static void print_isa(struct seq_file *f, const char *isa)
>>  {
>> --
>> 2.35.1
>>