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From:   Austin Kim <austindh.kim@gmail.com>
Date:   Fri, 28 May 2021 22:51:33 +0900
Message-ID: <CADLLry6AfRT6mGXnd66OV57YP4=m2PpOT5tom4QxVrOqGchw4w@mail.gmail.com>
Subject: Re: [PATCH] crypto: arm64/gcm - remove Wunused-const-variable ghash_cpu_feature
To:     Eric Biggers <ebiggers@kernel.org>
Cc:     herbert@gondor.apana.org.au, davem@davemloft.net,
        catalin.marinas@arm.com, will@kernel.org,
        John Johansen <john.johansen@canonical.com>, jmorris@namei.org,
        serge@hallyn.com, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-security-module@vger.kernel.org,
        linux-crypto@vger.kernel.org,
        =?UTF-8?B?6rmA64+Z7ZiE?= <austin.kim@lge.com>
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2021=EB=85=84 5=EC=9B=94 28=EC=9D=BC (=EA=B8=88) =EC=98=A4=EC=A0=84 2:46, E=
ric Biggers <ebiggers@kernel.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> On Thu, May 27, 2021 at 07:28:09AM +0100, Austin Kim wrote:
> >
> > The variable with MODULE_DEVICE_TABLE() is registered as platform_drive=
r.
>
> What does this mean?  There is no platform_driver involved here at all.
>

What I would like to say is "in many cases, MODULE_DEVICE_TABLE is
registered as struct of platform_driver"
ex) [drivers/char/hw_random/meson-rng.c]
MODULE_DEVICE_TABLE(of, meson_rng_of_match);

static struct platform_driver meson_rng_driver =3D {
.probe =3D meson_rng_probe,
.driver =3D {
.name =3D "meson-rng",
.of_match_table =3D meson_rng_of_match,
},
};

> > But ghash_cpu_feature is not used, so remove ghash_cpu_feature.
>
> It is used when the file is built as a module.
>

Thanks for the information. But it looks like this file is compiled
as built-in with 'CONFIG_CRYPTO_GHASH_ARM64_CE=3Dy' by default.

> > diff --git a/arch/arm64/crypto/ghash-ce-glue.c b/arch/arm64/crypto/ghas=
h-ce-glue.c
> > index 720cd3a58da3..c3f27d0d5329 100644
>>[...]
>
> Probably adding __maybe_unused to ghash_cpu_feature[] is the right thing =
to do.
> That's what module_cpu_feature_match() does.
>
> (Note that module_cpu_feature_match() can't be used here, as it seems the=
 intent
> is for this module to be autoloaded when PMULL is detected, but still be
> loadable without it.  So, that's apparently the reason for using
> MODULE_DEVICE_TABLE() directly.)

Thanks for the valuable idea and feedback.

>
> - Eric