From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2CAD6C33CB6 for ; Thu, 16 Jan 2020 19:57:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 04BFA2072B for ; Thu, 16 Jan 2020 19:57:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733179AbgAPT5Y (ORCPT ); Thu, 16 Jan 2020 14:57:24 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:53194 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726925AbgAPT5X (ORCPT ); Thu, 16 Jan 2020 14:57:23 -0500 Received: from p5b06da22.dip0.t-ipconnect.de ([91.6.218.34] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1isBGJ-0000KB-UP; Thu, 16 Jan 2020 20:57:04 +0100 Received: by nanos.tec.linutronix.de (Postfix, from userid 1000) id 6000B101226; Thu, 16 Jan 2020 20:57:03 +0100 (CET) From: Thomas Gleixner To: Andy Lutomirski , Christophe Leroy Cc: Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , nathanl@linux.ibm.com, Arnd Bergmann , Vincenzo Frascino , Andrew Lutomirski , LKML , linuxppc-dev , linux-arm-kernel , "open list\:MIPS" , X86 ML Subject: Re: [RFC PATCH v4 10/11] lib: vdso: Allow arches to override the ns shift operation In-Reply-To: References: Date: Thu, 16 Jan 2020 20:57:03 +0100 Message-ID: <877e1rfa40.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andy Lutomirski 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