Re: [PATCH v5 04/23] xen/asm-generic: introduce generic fls() and flsl() functions

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/02/2024 5:38 pm, Oleksii Kurochko wrote:
> These functions can be useful for architectures that don't
> have corresponding arch-specific instructions.
>
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> ---
>  Changes in V5:
>    - new patch
> ---
>  xen/include/asm-generic/bitops/fls.h  | 18 ++++++++++++++++++
>  xen/include/asm-generic/bitops/flsl.h | 10 ++++++++++
>  2 files changed, 28 insertions(+)
>  create mode 100644 xen/include/asm-generic/bitops/fls.h
>  create mode 100644 xen/include/asm-generic/bitops/flsl.h
>
> diff --git a/xen/include/asm-generic/bitops/fls.h 
> b/xen/include/asm-generic/bitops/fls.h
> new file mode 100644
> index 0000000000..369a4c790c
> --- /dev/null
> +++ b/xen/include/asm-generic/bitops/fls.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_GENERIC_BITOPS_FLS_H_
> +#define _ASM_GENERIC_BITOPS_FLS_H_
> +
> +/**
> + * fls - find last (most-significant) bit set
> + * @x: the word to search
> + *
> + * This is defined the same way as ffs.
> + * Note fls(0) = 0, fls(1) = 1, fls(0x80000000) = 32.
> + */
> +
> +static inline int fls(unsigned int x)
> +{
> +    return generic_fls(x);
> +}
> +
> +#endif /* _ASM_GENERIC_BITOPS_FLS_H_ */
> diff --git a/xen/include/asm-generic/bitops/flsl.h 
> b/xen/include/asm-generic/bitops/flsl.h
> new file mode 100644
> index 0000000000..d0a2e9c729
> --- /dev/null
> +++ b/xen/include/asm-generic/bitops/flsl.h
> @@ -0,0 +1,10 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _ASM_GENERIC_BITOPS_FLSL_H_
> +#define _ASM_GENERIC_BITOPS_FLSL_H_
> +
> +static inline int flsl(unsigned long x)
> +{
> +    return generic_flsl(x);
> +}
> +
> +#endif /* _ASM_GENERIC_BITOPS_FLSL_H_ */

Please don't do this.  It's compounding existing problems we have with
bitops, and there's a way to simplify things instead.

If you can wait a couple of days, I'll see about finishing and posting
my prototype demonstrating a simplification across all architectures,
and a reduction of code overall.

~Andrew