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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BB605C433F5 for ; Thu, 14 Apr 2022 10:12:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230462AbiDNKPK (ORCPT ); Thu, 14 Apr 2022 06:15:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49786 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230019AbiDNKPJ (ORCPT ); Thu, 14 Apr 2022 06:15:09 -0400 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C66886C927; Thu, 14 Apr 2022 03:12:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=upqcvBN0c/2twwWoHUne//eX4ki0XQTMtmfsi6ArAXU=; b=HjGPsWLJY1Ur/Qd9SaLg0YiKnR 95tjp26+YgI/HwEOdRqvSlAROO2sO63Z/uXu1t6/V5/PtASP1IW3k8kj55+7tgoHxaUyNfpLnuymj G+Nuireb4o2uAs9tgNLn8PCnmIvfeYm/3imhJXibehEvAyy2bcpTUxyuVWUQ0H1lRVoogDYJt+XGn +JXGGLKSFLPO1NgiG/h6Ou0ERgDMxxK3z39Afa9Ihp7G2oki6nDRlwzM4i7qfs+r/iBEJYNjoTAgZ nYexjH0hGr4I1XQ6yy/K0FsGtjU27thDPBNsh2vJZf5a5imdfgQbx4As5XreqUcbwl+Pi+VE00syg bbEnVKOQ==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:58256) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1newSp-0004M9-DZ; Thu, 14 Apr 2022 11:12:35 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1newSh-0004Du-6v; Thu, 14 Apr 2022 11:12:27 +0100 Date: Thu, 14 Apr 2022 11:12:27 +0100 From: "Russell King (Oracle)" To: "Jason A. Donenfeld" Cc: linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, tglx@linutronix.de, arnd@arndb.de, Theodore Ts'o , Dominik Brodowski , Catalin Marinas , Will Deacon , Geert Uytterhoeven , Thomas Bogendoerfer , Paul Walmsley , Palmer Dabbelt , Albert Ou , "David S . Miller" , Richard Weinberger , Anton Ivanov , Johannes Berg , Ingo Molnar , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Chris Zankel , Max Filippov , John Stultz , Stephen Boyd , Dinh Nguyen , linux-arm-kernel@lists.infradead.org, linux-m68k@lists.linux-m68k.org, linux-mips@vger.kernel.org, linux-riscv@lists.infradead.org, sparclinux@vger.kernel.org, linux-um@lists.infradead.org, x86@kernel.org, linux-xtensa@linux-xtensa.org Subject: Re: [PATCH v4 01/11] timekeeping: add raw clock fallback for random_get_entropy() Message-ID: References: <20220413115411.21489-1-Jason@zx2c4.com> <20220413115411.21489-2-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220413115411.21489-2-Jason@zx2c4.com> Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Wed, Apr 13, 2022 at 01:54:01PM +0200, Jason A. Donenfeld wrote: > The addition of random_get_entropy_fallback() provides access to > whichever time source has the highest frequency, which is useful for > gathering entropy on platforms without available cycle counters. It's > not necessarily as good as being able to quickly access a cycle counter > that the CPU has, but it's still something, even when it falls back to > being jiffies-based. > > In the event that a given arch does not define get_cycles(), falling > back to the get_cycles() default implementation that returns 0 is really > not the best we can do. Instead, at least calling > random_get_entropy_fallback() would be preferable, because that always > needs to return _something_, even falling back to jiffies eventually. > It's not as though random_get_entropy_fallback() is super high precision > or guaranteed to be entropic, but basically anything that's not zero all > the time is better than returning zero all the time. > > Cc: Thomas Gleixner > Cc: Arnd Bergmann > Cc: Theodore Ts'o > Signed-off-by: Jason A. Donenfeld > --- > include/linux/timex.h | 8 ++++++++ > kernel/time/timekeeping.c | 10 ++++++++++ > 2 files changed, 18 insertions(+) > > diff --git a/include/linux/timex.h b/include/linux/timex.h > index 5745c90c8800..fbbe34226044 100644 > --- a/include/linux/timex.h > +++ b/include/linux/timex.h > @@ -62,6 +62,8 @@ > #include > #include > > +extern unsigned long random_get_entropy_fallback(void); Hi I'm surprised this didn't trigger checkpatch to warn. From coding-style: 6.1) Function prototypes Do not use the ``extern`` keyword with function declarations as this makes lines longer and isn't strictly necessary. Thanks! -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!