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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 60CF2ECE58C for ; Fri, 11 Oct 2019 11:36:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3E3452190F for ; Fri, 11 Oct 2019 11:36:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727832AbfJKLgZ (ORCPT ); Fri, 11 Oct 2019 07:36:25 -0400 Received: from foss.arm.com ([217.140.110.172]:57514 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727226AbfJKLgY (ORCPT ); Fri, 11 Oct 2019 07:36:24 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0237528; Fri, 11 Oct 2019 04:36:24 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 050593F703; Fri, 11 Oct 2019 04:36:22 -0700 (PDT) Date: Fri, 11 Oct 2019 12:36:20 +0100 From: Dave Martin To: Suzuki K Poulose Cc: linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, will@kernel.org Subject: Re: [PATCH 1/3] arm64: cpufeature: Fix the type of no FP/SIMD capability Message-ID: <20191011113620.GG27757@arm.com> References: <20191010171517.28782-1-suzuki.poulose@arm.com> <20191010171517.28782-2-suzuki.poulose@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191010171517.28782-2-suzuki.poulose@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 10, 2019 at 06:15:15PM +0100, Suzuki K Poulose wrote: > The NO_FPSIMD capability is defined with scope SYSTEM, which implies > that the "absence" of FP/SIMD on at least one CPU is detected only > after all the SMP CPUs are brought up. However, we use the status > of this capability for every context switch. So, let us change > the scop to LOCAL_CPU to allow the detection of this capability > as and when the first CPU without FP is brought up. > > Also, the current type allows hotplugged CPU to be brought up without > FP/SIMD when all the current CPUs have FP/SIMD and we have the userspace > up. Fix both of these issues by changing the capability to > BOOT_RESTRICTED_LOCAL_CPU_FEATURE. > > Fixes: 82e0191a1aa11abf ("arm64: Support systems without FP/ASIMD") > Cc: Will Deacon > Cc: Mark Rutland > Cc: Catalin Marinas > Signed-off-by: Suzuki K Poulose > --- > arch/arm64/kernel/cpufeature.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c > index 9323bcc40a58..0f9eace6c64b 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1361,7 +1361,7 @@ static const struct arm64_cpu_capabilities arm64_features[] = { > { > /* FP/SIMD is not implemented */ > .capability = ARM64_HAS_NO_FPSIMD, > - .type = ARM64_CPUCAP_SYSTEM_FEATURE, > + .type = ARM64_CPUCAP_BOOT_RESTRICTED_CPU_LOCAL_FEATURE, ARM64_HAS_NO_FPSIMD is really a disability, not a capability. Although we have other things that smell like this (CPU errata for example), I wonder whether inverting the meaning in the case would make the situation easier to understand. So, we'd have ARM64_HAS_FPSIMD, with a minimum (signed) feature field value of 0. Then this just looks like an ARM64_CPUCAP_SYSTEM_FEATURE IIUC. We'd just need to invert the sense of the check in system_supports_fpsimd(). > .min_field_value = 0, (Does .min_field_value == 0 make sense, or is it even used? I thought only the default has_cpuid_feature() match logic uses that.) > .matches = has_no_fpsimd, > }, Cheers ---Dave