linux-kernel - Re: [PATCH v2 04/13] RISC-V: crypto: add Zvkned accelerated AES implementation

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Date:   Wed, 29 Nov 2023 10:39:56 +0800
From:   Jerry Shih <jerry.shih@...ive.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Conor Dooley <conor@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>, palmer@...belt.com,
        aou@...s.berkeley.edu, herbert@...dor.apana.org.au,
        davem@...emloft.net, conor.dooley@...rochip.com, ardb@...nel.org,
        heiko@...ech.de, phoebe.chen@...ive.com, hongrong.hsu@...ive.com,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-crypto@...r.kernel.org
Subject: Re: [PATCH v2 04/13] RISC-V: crypto: add Zvkned accelerated AES
 implementation

On Nov 29, 2023, at 04:12, Eric Biggers <ebiggers@...nel.org> wrote:
> On Tue, Nov 28, 2023 at 05:54:49PM +0000, Conor Dooley wrote:
>>> +static inline bool check_aes_ext(void)
>>> +{
>>> +	return riscv_isa_extension_available(NULL, ZVKNED) &&
>>> +	       riscv_vector_vlen() >= 128;
>>> +}
>> 
>> I'm not keen on this construct, where you are checking vlen greater than
>> 128 and the presence of Zvkned without checking for the presence of V
>> itself. Can you use "has_vector()" in any places where you depend on the
>> presence of vector please?
> 
> Shouldn't both of those things imply vector support already?

The vector crypto extensions imply `V` extension. Should we still need to check
the `V` explicitly?
https://github.com/riscv/riscv-crypto/blob/main/doc/vector/riscv-crypto-spec-vector.adoc#1-extensions-overview

>> Also, there are potentially a lot of places in this drivers where you
>> can replace "riscv_isa_extension_available()" with
>> "riscv_has_extension_likely()". The latter is optimised with
>> alternatives, so in places that are going to be evaluated frequently it
>> may be beneficial for you.
> 
> These extension checks are only executed in module_init functions, so they're
> not performance critical.

All `riscv_isa_extension_available()` calls in crypto drivers are called once
in the module init calls. Should we still need that `riscv_has_extension_likely()`
with a little more code size?

> - Eric