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From: Thomas Gleixner <tglx@linutronix.de>
To: Andy Lutomirski <luto@kernel.org>,
 Christophe Leroy <christophe.leroy@c-s.fr>
Subject: Re: [RFC PATCH v4 10/11] lib: vdso: Allow arches to override the ns
 shift operation
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Date: Thu, 16 Jan 2020 20:57:03 +0100
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Andy Lutomirski <luto@kernel.org> 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:

     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