linux-kernel - Re: [PATCH v2 2/6] RISC-V: Add a syscall for HW probing

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Date:   Tue, 07 Feb 2023 06:32:18 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Evan Green <evan@...osinc.com>
CC:     Palmer Dabbelt <palmer@...osinc.com>, vineetg@...osinc.com,
        heiko@...ech.de, slewis@...osinc.com,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Bresticker <abrestic@...osinc.com>,
        Andrew Jones <ajones@...tanamicro.com>,
        Anup Patel <apatel@...tanamicro.com>,
        Arnd Bergmann <arnd@...db.de>,
        Atish Patra <atishp@...osinc.com>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Celeste Liu <coelacanthus@...look.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        Dao Lu <daolu@...osinc.com>, Guo Ren <guoren@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ruizhe Pan <c141028@...il.com>,
        Sunil V L <sunilvl@...tanamicro.com>,
        Tobias Klauser <tklauser@...tanz.ch>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 2/6] RISC-V: Add a syscall for HW probing

Hey Evan, Greg,


On 7 February 2023 06:13:39 GMT, Greg KH <gregkh@...uxfoundation.org> wrote:
>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 no
>> system call that quite does this, so let's just provide an arch-specific
>> one to probe for hardware capabilities.  This currently just provides
>> m{arch,imp,vendor}id, but with the key-value pairs we can pass more in
>> the future.
>
>Ick, this is exactly what sysfs is designed to export in a sane way.
>Why not just use that instead?  The "key" would be the filename, and the
>value the value read from the filename.  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.

https://lore.kernel.org/linux-riscv/20221201160614.xpomlqq2fzpzfmcm@kamzik/

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

>
>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.
>
>thanks,
>
>greg k-h