From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756877AbbJHL4c (ORCPT ); Thu, 8 Oct 2015 07:56:32 -0400 Received: from eu-smtp-delivery-143.mimecast.com ([207.82.80.143]:48033 "EHLO eu-smtp-delivery-143.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755291AbbJHL4b convert rfc822-to-8bit (ORCPT ); Thu, 8 Oct 2015 07:56:31 -0400 Subject: Re: [PATCH v2 16/22] arm64/debug: Make use of the system wide safe value To: Catalin Marinas References: <1444064531-25607-1-git-send-email-suzuki.poulose@arm.com> <1444064531-25607-17-git-send-email-suzuki.poulose@arm.com> <20151008111128.GH17192@e104818-lin.cambridge.arm.com> Cc: linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, Vladimir.Murzin@arm.com, steve.capper@linaro.org, ard.biesheuvel@linaro.org, marc.zyngier@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, edward.nevill@linaro.org, aph@redhat.com, james.morse@arm.com, andre.przywara@arm.com, dave.martin@arm.com From: "Suzuki K. Poulose" Message-ID: <561659EC.7030508@arm.com> Date: Thu, 8 Oct 2015 12:56:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20151008111128.GH17192@e104818-lin.cambridge.arm.com> X-OriginalArrivalTime: 08 Oct 2015 11:56:28.0509 (UTC) FILETIME=[5D8968D0:01D101C0] X-MC-Unique: va8Gqmo2QsG66w47e5DxPQ-1 Content-Type: text/plain; charset=WINDOWS-1252; format=flowed Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/10/15 12:11, Catalin Marinas wrote: > On Mon, Oct 05, 2015 at 06:02:05PM +0100, Suzuki K. Poulose wrote: >> @@ -137,13 +138,17 @@ extern struct pmu perf_ops_bp; >> /* Determine number of BRP registers available. */ >> static inline int get_num_brps(void) >> { >> - return ((read_cpuid(ID_AA64DFR0_EL1) >> 12) & 0xf) + 1; >> + return 1 + >> + cpuid_feature_extract_field(read_system_reg(SYS_ID_AA64DFR0_EL1), >> + ID_AA64DFR0_BRPS_SHIFT); >> } > > cpuid_feature_extract_field() is fine but we should we bother with > read_system_reg vs just read_cpuid? > Similar question for patch 17/22. Well, we would have already TAINTed the kernel, if these fields are different. It is just the matter of, whether we want to provide the safer value on a tainted kernel or not. I am open to suggestions. Thanks Suzuki