[PATCH 2/2] bitops: rotate: Add riscv implementation using Zbb extension

[cp0613 at linux.alibaba.com]

On Fri, 20 Jun 2025 12:20:47 -0400, yury.norov at gmail.com wrote:

> Can you add a comment about what is happening here? Are you sure it's
> optimized out in case of the 'legacy' alternative?

Thank you for your review. Yes, I referred to the existing variable__fls()
implementation, which should be fine.

> Here you wire ror/rol() to the variable_ror/rol() unconditionally, and
> that breaks compile-time rotation if the parameter is known at compile
> time.
> 
> I believe, generic implementation will allow compiler to handle this
> case better. Can you do a similar thing to what fls() does in the same
> file?

I did consider it, but I did not find any toolchain that provides an
implementation similar to __builtin_ror or __builtin_rol. If there is one,
please help point it out.
In addition, I did not consider it carefully before. If the rotate function
is to be genericized, all archneed to include <asm-generic/bitops/rotate.h>.
I missed this step.