Re: [RFC PATCH v4 10/11] lib: vdso: Allow arches to override the ns shift operation

[Andy Lutomirski]

On Thu, Jan 16, 2020 at 11:57 AM Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
>
> Andy Lutomirski <luto@xxxxxxxxxx> writes:
> > On Thu, Jan 16, 2020 at 9:58 AM Christophe Leroy
> >
> > Would mul_u64_u64_shr() be a good alternative?  Could we adjust it to
> > assume the shift is less than 32?  That function exists to benefit
> > 32-bit arches.
>
> We'd want mul_u64_u32_shr() for this. The rules for mult and shift are:
>

That's what I meant to type...

>      1 <= mult <= U32_MAX
>
>      1 <= shift <= 32
>
> If we want to enforce a shift < 32 we need to limit that conditionally
> in the calculation/registration function.
>
> Thanks,
>
>         tglx
>