linux-kernel - Re: [PATCH v5 1/4] RISC-V: add Zbc extension detection

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Message-ID: <mhng-5286e1ed-b3ae-40ce-bd33-8871a1a07f3a@palmer-ri-x1c9a>
Date:   Tue, 20 Jun 2023 12:42:11 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Jeff Law <jlaw@...tanamicro.com>
CC:     Conor Dooley <conor@...nel.org>, heiko@...ech.de,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, herbert@...dor.apana.org.au,
        davem@...emloft.net, Conor Dooley <conor.dooley@...rochip.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org, christoph.muellner@...ll.eu,
        heiko.stuebner@...ll.eu
Subject:     Re: [PATCH v5 1/4] RISC-V: add Zbc extension detection

On Tue, 20 Jun 2023 12:37:00 PDT (-0700), Jeff Law wrote:
>
>
> On 6/20/23 13:09, Palmer Dabbelt wrote:
>> On Mon, 12 Jun 2023 14:31:14 PDT (-0700), Conor Dooley wrote:
>>> Hey Heiko,
>>>
>>> On Mon, Jun 12, 2023 at 11:04:39PM +0200, Heiko Stuebner wrote:
>>>> From: Heiko Stuebner <heiko.stuebner@...ll.eu>
>>>>
>>>> Add handling for Zbc extension.
>>>>
>>>> Zbc provides instruction for carry-less multiplication.
>>>>
>>>> Signed-off-by: Heiko Stuebner <heiko.stuebner@...ll.eu>
>>>> ---
>>>>  arch/riscv/Kconfig             | 22 ++++++++++++++++++++++
>>>>  arch/riscv/include/asm/hwcap.h |  1 +
>>>>  arch/riscv/kernel/cpu.c        |  1 +
>>>>  arch/riscv/kernel/cpufeature.c |  1 +
>>>>  4 files changed, 25 insertions(+)
>>>
>>> Plumbing into the hwprobe stuff would be nice, but that's not a
>>> requirement for getting stuff merged :)
>>
>> IIRC we talked about this on IRC, but IMO we shouldn't require something
>> be user visible for it to be merged in the kernel.
> Note that exposing Zbc is potentially useful.  We've got GCC and LLVM
> code that can detect and rewrite a bitwise CRC into clmul.

Ya, there's another thread about adding it.  IMO we should do so, just 
that we shouldn't gate kernel support on also sorting out the uABI as 
sometimes that's complicated.

It's simple for this one, though, so I'm not opposed to taking it for 
the merge window if it shows up in the next day or two...

>
> Jeff