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=-9.0 required=3.0 tests=BAYES_00,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 6B4A9C2B9F7 for ; Wed, 26 May 2021 08:32:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3F904613BC for ; Wed, 26 May 2021 08:32:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233011AbhEZIdk (ORCPT ); Wed, 26 May 2021 04:33:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:53302 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232209AbhEZIdf (ORCPT ); Wed, 26 May 2021 04:33:35 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id A8E6D61402; Wed, 26 May 2021 08:32:04 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1lloxO-003gbK-JB; Wed, 26 May 2021 09:32:02 +0100 Date: Wed, 26 May 2021 09:32:01 +0100 Message-ID: <871r9tx5dq.wl-maz@kernel.org> From: Marc Zyngier To: Geert Uytterhoeven Cc: jianyong.wu@arm.com, netdev , Yangbo Lu , John Stultz , Thomas Gleixner , Paolo Bonzini , seanjc@google.com, Richard Cochran , Mark Rutland , Will Deacon , Suzuki K Poulose , Andre Przywara , Steven Price , Lorenzo Pieralisi , Sudeep Holla , Linux Kernel Mailing List , Linux ARM , kvmarm@lists.cs.columbia.edu, KVM list , Steve Capper , justin.he@arm.com, Android Kernel Team Subject: Re: [PATCH v19 7/7] ptp: arm/arm64: Enable ptp_kvm for arm/arm64 In-Reply-To: References: <20210330145430.996981-1-maz@kernel.org> <20210330145430.996981-8-maz@kernel.org> <6c522f8116f54fa6f23a2d217d966c5a@kernel.org> <8735u9x6sb.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: geert@linux-m68k.org, jianyong.wu@arm.com, netdev@vger.kernel.org, yangbo.lu@nxp.com, john.stultz@linaro.org, tglx@linutronix.de, pbonzini@redhat.com, seanjc@google.com, richardcochran@gmail.com, Mark.Rutland@arm.com, will@kernel.org, suzuki.poulose@arm.com, Andre.Przywara@arm.com, steven.price@arm.com, lorenzo.pieralisi@arm.com, sudeep.holla@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, Steve.Capper@arm.com, justin.he@arm.com, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, 26 May 2021 09:18:27 +0100, Geert Uytterhoeven wrote: > > Hi Marc, > > On Wed, May 26, 2021 at 10:01 AM Marc Zyngier wrote: > > On Wed, 26 May 2021 08:52:42 +0100, > > Geert Uytterhoeven wrote: > > > On Tue, May 11, 2021 at 11:13 AM Marc Zyngier wrote: > > > > On 2021-05-11 10:07, Geert Uytterhoeven wrote: > > > > > On Tue, Mar 30, 2021 at 4:56 PM Marc Zyngier wrote: > > > > >> From: Jianyong Wu > > > > > > > > > >> --- a/drivers/ptp/Kconfig > > > > >> +++ b/drivers/ptp/Kconfig > > > > >> @@ -108,7 +108,7 @@ config PTP_1588_CLOCK_PCH > > > > >> config PTP_1588_CLOCK_KVM > > > > >> tristate "KVM virtual PTP clock" > > > > >> depends on PTP_1588_CLOCK > > > > >> - depends on KVM_GUEST && X86 > > > > >> + depends on (KVM_GUEST && X86) || (HAVE_ARM_SMCCC_DISCOVERY && > > > > >> ARM_ARCH_TIMER) > > > > > > > > > > Why does this not depend on KVM_GUEST on ARM? > > > > > I.e. shouldn't the dependency be: > > > > > > > > > > KVM_GUEST && (X86 || (HAVE_ARM_SMCCC_DISCOVERY && ARM_ARCH_TIMER)) > > > > > > > > > > ? > > > > > > > > arm/arm64 do not select KVM_GUEST. Any kernel can be used for a guest, > > > > and KVM/arm64 doesn't know about this configuration symbol. > > > > > > OK. > > > > > > Does PTP_1588_CLOCK_KVM need to default to yes? > > > Perhaps only on X86, to maintain the status quo? > > > > I think I don't really understand the problem you are trying to > > solve. Is it that 'make oldconfig' now asks you about this new driver? > > Why is that an issue? > > My first "problem" was that it asked about this new driver on > arm/arm64, while I assumed there were some missing dependencies > (configuring a kernel should not ask useless questions). That turned > out to be a wrong assumption, so there is no such problem here. > > The second problem is "default y": code that is not critical should > not be enabled by default. Hence my last question. I think consistency between architectures is important. Certainly, distributions depend on that, and we otherwise end-up with distro kernels missing functionalities. The notion of "critical" is also pretty relative. defconfig contains a gazillion of things that are not critical to most people, for example, and yet misses a bunch of things that are needed to boot on some of my systems. That's just to say that I find it difficult to make that choice from the PoV of a kernel hacker. I'm personally more inclined to leave things enabled and let people *disable* things if they want to reduce the footprint of their kernel. Thanks, M. -- Without deviation from the norm, progress is not possible.