Re: [PATCH v2 1/2] bitops: Define generic __bitrev8/16/32 for reuse

From: Yury Norov <ynorov@nvidia.com>
To: Jinjie Ruan <ruanjinjie@huawei.com>
Cc: pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu,
	alex@ghiti.fr, yury.norov@gmail.com, linux@rasmusvillemoes.dk,
	arnd@arndb.de, cp0613@linux.alibaba.com,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-arch@vger.kernel.org
Subject: Re: [PATCH v2 1/2] bitops: Define generic __bitrev8/16/32 for reuse
Date: Wed, 15 Apr 2026 14:30:04 -0400	[thread overview]
Message-ID: <ad_ZLNslqjpYRJvW@yury> (raw)
In-Reply-To: <20260415093827.2776328-2-ruanjinjie@huawei.com>

On Wed, Apr 15, 2026 at 05:38:26PM +0800, Jinjie Ruan wrote:
> Define generic __bitrev8/16/32 using the implementation
> in <linux/bitrev.h>, so they can be reused in <asm/bitrev.h>,
> such as RISCV.
> 
> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>

Reviewed-by: Yury Norov <ynorov@nvidia.com>

I'll take it in -next for testing. That would help to catch some
probable warnings discussed in the #2.

> ---
>  include/asm-generic/bitops/__bitrev.h | 22 ++++++++++++++++++++++
>  include/linux/bitrev.h                | 20 ++++----------------
>  2 files changed, 26 insertions(+), 16 deletions(-)
>  create mode 100644 include/asm-generic/bitops/__bitrev.h
> 
> diff --git a/include/asm-generic/bitops/__bitrev.h b/include/asm-generic/bitops/__bitrev.h
> new file mode 100644
> index 000000000000..1b8c0f464d26
> --- /dev/null
> +++ b/include/asm-generic/bitops/__bitrev.h
> @@ -0,0 +1,22 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_GENERIC_BITOPS___BITREV_H_
> +#define _ASM_GENERIC_BITOPS___BITREV_H_
> +
> +#include <asm/types.h>
> +
> +extern u8 const byte_rev_table[256];
> +static __always_inline __attribute_const__ u8 generic___bitrev8(u8 byte)
> +{
> +	return byte_rev_table[byte];
> +}
> +
> +static __always_inline __attribute_const__ u16 generic___bitrev16(u16 x)
> +{
> +	return (generic___bitrev8(x & 0xff) << 8) | generic___bitrev8(x >> 8);
> +}
> +
> +static __always_inline __attribute_const__ u32 generic___bitrev32(u32 x)
> +{
> +	return (generic___bitrev16(x & 0xffff) << 16) | generic___bitrev16(x >> 16);
> +}
> +#endif /* _ASM_GENERIC_BITOPS___BITREV_H_ */
> diff --git a/include/linux/bitrev.h b/include/linux/bitrev.h
> index d35b8ec1c485..11620a70e776 100644
> --- a/include/linux/bitrev.h
> +++ b/include/linux/bitrev.h
> @@ -12,22 +12,10 @@
>  #define __bitrev8 __arch_bitrev8
>  
>  #else
> -extern u8 const byte_rev_table[256];
> -static inline u8 __bitrev8(u8 byte)
> -{
> -	return byte_rev_table[byte];
> -}
> -
> -static inline u16 __bitrev16(u16 x)
> -{
> -	return (__bitrev8(x & 0xff) << 8) | __bitrev8(x >> 8);
> -}
> -
> -static inline u32 __bitrev32(u32 x)
> -{
> -	return (__bitrev16(x & 0xffff) << 16) | __bitrev16(x >> 16);
> -}
> -
> +#include <asm-generic/bitops/__bitrev.h>
> +#define __bitrev32 generic___bitrev32
> +#define __bitrev16 generic___bitrev16
> +#define __bitrev8 generic___bitrev8
>  #endif /* CONFIG_HAVE_ARCH_BITREVERSE */
>  
>  #define __bitrev8x4(x)	(__bitrev32(swab32(x)))
> -- 
> 2.34.1

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