Date:   Tue, 07 Feb 2023 06:32:18 +0000
From:   Conor Dooley <conor@kernel.org>
To:     Greg KH <gregkh@linuxfoundation.org>,
        Evan Green <evan@rivosinc.com>
CC:     Palmer Dabbelt <palmer@rivosinc.com>, vineetg@rivosinc.com,
        heiko@sntech.de, slewis@rivosinc.com,
        Albert Ou <aou@eecs.berkeley.edu>,
        Andrew Bresticker <abrestic@rivosinc.com>,
        Andrew Jones <ajones@ventanamicro.com>,
        Anup Patel <apatel@ventanamicro.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Atish Patra <atishp@rivosinc.com>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        Celeste Liu <coelacanthus@outlook.com>,
        Conor Dooley <conor.dooley@microchip.com>,
        Dao Lu <daolu@rivosinc.com>, Guo Ren <guoren@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
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        Ruizhe Pan <c141028@gmail.com>,
        Sunil V L <sunilvl@ventanamicro.com>,
        Tobias Klauser <tklauser@distanz.ch>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org
Subject: Re: [PATCH v2 2/6] RISC-V: Add a syscall for HW probing
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Hey Evan, Greg,


On 7 February 2023 06:13:39 GMT, Greg KH <gregkh@linuxfoundation=2Eorg> wr=
ote:
>On Mon, Feb 06, 2023 at 12:14:51PM -0800, Evan Green wrote:
>> We don't have enough space for these all in ELF_HWCAP{,2} and there's n=
o
>> system call that quite does this, so let's just provide an arch-specifi=
c
>> one to probe for hardware capabilities=2E  This currently just provides
>> m{arch,imp,vendor}id, but with the key-value pairs we can pass more in
>> the future=2E
>
>Ick, this is exactly what sysfs is designed to export in a sane way=2E
>Why not just use that instead?  The "key" would be the filename, and the
>value the value read from the filename=2E  If the key is not present, the
>file is not present and it's obvious what is happening, no fancy parsing
>and ABI issues at all=2E

https://lore=2Ekernel=2Eorg/linux-riscv/20221201160614=2Expomlqq2fzpzfmcm@=
kamzik/

This is the sysfs interface that I mentioned drew
suggested on the v1=2E
I think it fits ~perfectly with what Greg is suggesting too=2E

>
>Bonus is that you will also properly document all valid key/value pairs
>in Documentation/ABI/ when you do this, so it reinforces what the code
>should be doing correctly=2E
>
>thanks,
>
>greg k-h