Re: [PATCH v2 1/5] arch: select HAVE_ARCH_BITREVERSE conditionally on BITREVERSE

From: Yury Norov <ynorov@nvidia.com>
To: Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Yury Norov <yury.norov@gmail.com>,
	Rasmus Villemoes <linux@rasmusvillemoes.dk>,
	Arnd Bergmann <arnd@arndb.de>, Eric Biggers <ebiggers@kernel.org>,
	Andrew Lunn <andrew+netdev@lunn.ch>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	Stanislav Fomichev <sdf@fomichev.me>,
	Jinjie Ruan <ruanjinjie@huawei.com>,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-arch@vger.kernel.org, netdev@vger.kernel.org,
	bpf@vger.kernel.org
Subject: Re: [PATCH v2 1/5] arch: select HAVE_ARCH_BITREVERSE conditionally on BITREVERSE
Date: Tue, 19 May 2026 18:20:34 -0400	[thread overview]
Message-ID: <agziMgYIg96fTVst@yury> (raw)
In-Reply-To: <agKPkFq6kuarikAJ@yury>

Ping again?

On Mon, May 11, 2026 at 10:25:20PM -0400, Yury Norov wrote:
> Ping?
> 
> On Wed, May 06, 2026 at 01:52:02PM -0400, Yury Norov wrote:
> > Architectures may have bit reversal instructions, but if the API not
> > needed, the corresponding option should not be selected because it may
> > lead to generating the unneeded code.
> > 
> > Signed-off-by: Yury Norov <ynorov@nvidia.com>
> > ---
> >  arch/arm/Kconfig       | 2 +-
> >  arch/arm64/Kconfig     | 2 +-
> >  arch/loongarch/Kconfig | 2 +-
> >  arch/mips/Kconfig      | 2 +-
> >  lib/Kconfig            | 1 +
> >  5 files changed, 5 insertions(+), 4 deletions(-)
> > 
> > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> > index 71fc5dd4123f..0e963e54fe06 100644
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -83,7 +83,7 @@ config ARM
> >  	select HARDIRQS_SW_RESEND
> >  	select HAS_IOPORT
> >  	select HAVE_ARCH_AUDITSYSCALL if AEABI && !OABI_COMPAT
> > -	select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6
> > +	select HAVE_ARCH_BITREVERSE if (CPU_32v7M || CPU_32v7) && !CPU_32v6 && BITREVERSE
> >  	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL && !CPU_ENDIAN_BE32 && MMU && (!PREEMPT_RT || !SMP)
> >  	select HAVE_ARCH_KFENCE if MMU && !XIP_KERNEL
> >  	select HAVE_ARCH_KGDB if !CPU_ENDIAN_BE32 && MMU
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index fe60738e5943..f5bb62c2ba9c 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -150,7 +150,7 @@ config ARM64
> >  	select HAVE_ACPI_APEI if (ACPI && EFI)
> >  	select HAVE_ALIGNED_STRUCT_PAGE
> >  	select HAVE_ARCH_AUDITSYSCALL
> > -	select HAVE_ARCH_BITREVERSE
> > +	select HAVE_ARCH_BITREVERSE if BITREVERSE
> >  	select HAVE_ARCH_COMPILER_H
> >  	select HAVE_ARCH_HUGE_VMALLOC
> >  	select HAVE_ARCH_HUGE_VMAP
> > diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> > index 3b042dbb2c41..6c3444e31c0e 100644
> > --- a/arch/loongarch/Kconfig
> > +++ b/arch/loongarch/Kconfig
> > @@ -115,7 +115,7 @@ config LOONGARCH
> >  	select HAS_IOPORT
> >  	select HAVE_ALIGNED_STRUCT_PAGE if 64BIT
> >  	select HAVE_ARCH_AUDITSYSCALL
> > -	select HAVE_ARCH_BITREVERSE if 64BIT
> > +	select HAVE_ARCH_BITREVERSE if 64BIT && BITREVERSE
> >  	select HAVE_ARCH_JUMP_LABEL
> >  	select HAVE_ARCH_JUMP_LABEL_RELATIVE
> >  	select HAVE_ARCH_KASAN if 64BIT
> > diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> > index 4364f3dba688..7e1494e0dbfa 100644
> > --- a/arch/mips/Kconfig
> > +++ b/arch/mips/Kconfig
> > @@ -2026,7 +2026,7 @@ config CPU_MIPSR6
> >  	default y if CPU_MIPS32_R6 || CPU_MIPS64_R6
> >  	select CPU_HAS_RIXI
> >  	select CPU_HAS_DIEI if !CPU_DIEI_BROKEN
> > -	select HAVE_ARCH_BITREVERSE
> > +	select HAVE_ARCH_BITREVERSE if BITREVERSE
> >  	select MIPS_ASID_BITS_VARIABLE
> >  	select MIPS_SPRAM
> >  
> > diff --git a/lib/Kconfig b/lib/Kconfig
> > index 00a9509636c1..d8e7e89ae320 100644
> > --- a/lib/Kconfig
> > +++ b/lib/Kconfig
> > @@ -58,6 +58,7 @@ config BITREVERSE
> >  config HAVE_ARCH_BITREVERSE
> >  	bool
> >  	default n
> > +	depends on BITREVERSE
> >  	help
> >  	  This option enables the use of hardware bit-reversal instructions on
> >  	  architectures which support such operations.
> > -- 
> > 2.51.0