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Date:   Wed, 15 Feb 2023 10:56:51 +0100
From:   "Arnd Bergmann" <arnd@arndb.de>
To:     "Evan Green" <evan@rivosinc.com>,
        "Palmer Dabbelt" <palmer@rivosinc.com>
Cc:     "Conor Dooley" <conor@kernel.org>,
        "Vineet Gupta" <vineetg@rivosinc.com>,
        =?UTF-8?Q?Heiko_St=C3=BCbner?= <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>,
        "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>, guoren <guoren@kernel.org>,
        "Jonathan Corbet" <corbet@lwn.net>,
        "Palmer Dabbelt" <palmer@dabbelt.com>,
        "Paul Walmsley" <paul.walmsley@sifive.com>,
        "Randy Dunlap" <rdunlap@infradead.org>,
        "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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On Mon, Feb 6, 2023, at 21:14, 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.
>
> Co-developed-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> Signed-off-by: Evan Green <evan@rivosinc.com>

I'm not sure I understand the problem with
AT_HWCAP. While the bits in AT_HWCAP and AT_HWCAP2
are limited, I don't see us running out of new
AT_* words to use for additional bits. Presumably
the kernel would already have to know about the
name of each supported HW feature and could assign
a unique bit number to them.

      Arnd