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

[Oleksii <oleksii.kurochko@xxxxxxxxx>]

On Thu, 2024-02-29 at 16:25 +0000, Andrew Cooper wrote:
> 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.
Please add me in CC.

~ Oleksii