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Date:   Fri, 4 Oct 2019 16:00:57 +0200
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     linux-crypto@vger.kernel.org,
        Herbert Xu <herbert@gondor.apana.org.au>,
        David Miller <davem@davemloft.net>,
        Greg KH <gregkh@linuxfoundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Samuel Neves <sneves@dei.uc.pt>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Eric Biggers <ebiggers@google.com>,
        Andy Lutomirski <luto@kernel.org>,
        Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Martin Willi <martin@strongswan.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH v2 18/20] crypto: arm/Curve25519 - wire up NEON
 implementation
Message-ID: <20191004140057.GB114360@zx2c4.com>
References: <20191002141713.31189-1-ard.biesheuvel@linaro.org>
 <20191002141713.31189-19-ard.biesheuvel@linaro.org>
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On Wed, Oct 02, 2019 at 04:17:11PM +0200, Ard Biesheuvel wrote:
> +bool curve25519_arch(u8 out[CURVE25519_KEY_SIZE],
> +		     const u8 scalar[CURVE25519_KEY_SIZE],
> +		     const u8 point[CURVE25519_KEY_SIZE])
> +{
> +	if (!have_neon || !crypto_simd_usable())
> +		return false;
> +	kernel_neon_begin();
> +	curve25519_neon(out, scalar, point);
> +	kernel_neon_end();
> +	return true;
> +}
> +EXPORT_SYMBOL(curve25519_arch);

This now looks more like the Zinc way of doing things, with the _arch
function returning true or false based on whether or not the
implementation was available, allowing the generic implementation to
run.

I thought, from looking at the chacha commits earlier, you had done away
with that style of things in favor of weak symbols, whereby the arch
implementation would fall back to the generic one, instead of the other
way around?