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From: Andy Lutomirski <luto@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Paul Mackerras <paulus@samba.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	nathanl@linux.ibm.com, Arnd Bergmann <arnd@arndb.de>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Andrew Lutomirski <luto@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	"open list:MIPS" <linux-mips@vger.kernel.org>,
	X86 ML <x86@kernel.org>
Subject: Re: [RFC PATCH v4 10/11] lib: vdso: Allow arches to override the ns shift operation
Date: Thu, 16 Jan 2020 12:20:59 -0800
Message-ID: <CALCETrX5B0SEJN2WG7rzuzbGhWa_dEwVVpMu6deXof3H+K_LdQ@mail.gmail.com> (raw)
In-Reply-To: <877e1rfa40.fsf@nanos.tec.linutronix.de>

On Thu, Jan 16, 2020 at 11:57 AM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> 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:
>

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
>

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16 17:58 [RFC PATCH v4 00/11] powerpc: switch VDSO to C implementation Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 01/11] powerpc/64: Don't provide time functions in compat VDSO32 Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 02/11] powerpc/vdso: Switch VDSO to generic C implementation Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 03/11] lib: vdso: only read hrtimer_res when needed in __cvdso_clock_getres() Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 04/11] powerpc/vdso: simplify __get_datapage() Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 05/11] lib: vdso: allow arches to provide vdso data pointer Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 06/11] powerpc/vdso: provide inline alternative to __get_datapage() Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 07/11] powerpc/vdso: provide vdso data pointer from the ASM caller Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 08/11] lib: vdso: allow fixed clock mode Christophe Leroy
2020-01-16 20:13   ` Thomas Gleixner
2020-01-16 20:19     ` Andy Lutomirski
2020-01-16 21:07       ` Thomas Gleixner
2020-01-16 17:58 ` [RFC PATCH v4 09/11] powerpc/vdso: override __arch_vdso_capable() Christophe Leroy
2020-01-16 17:58 ` [RFC PATCH v4 10/11] lib: vdso: Allow arches to override the ns shift operation Christophe Leroy
2020-01-16 19:47   ` Andy Lutomirski
2020-01-16 19:57     ` Thomas Gleixner
2020-01-16 20:20       ` Andy Lutomirski [this message]
2020-01-16 17:58 ` [RFC PATCH v4 11/11] powerpc/32: provide vdso_shift_ns() Christophe Leroy
2020-01-17  8:58 ` [RFC PATCH v4 00/11] powerpc: switch VDSO to C implementation Segher Boessenkool
2020-01-17  9:26   ` Christophe Leroy

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