From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753721AbeBGLz0 (ORCPT ); Wed, 7 Feb 2018 06:55:26 -0500 Received: from foss.arm.com ([217.140.101.70]:49860 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753470AbeBGLzZ (ORCPT ); Wed, 7 Feb 2018 06:55:25 -0500 Date: Wed, 7 Feb 2018 11:55:21 +0000 From: Dave Martin To: Suzuki K Poulose Cc: mark.rutland@arm.com, catalin.marinas@arm.com, will.deacon@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 2/2] arm64: Expose Arm v8.4 features Message-ID: <20180207115521.GO5862@e103592.cambridge.arm.com> References: <20180201103838.14702-1-suzuki.poulose@arm.com> <20180201103838.14702-2-suzuki.poulose@arm.com> <20180207104320.GM5862@e103592.cambridge.arm.com> <336948e9-62c4-1ca0-c832-045095eda229@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <336948e9-62c4-1ca0-c832-045095eda229@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 07, 2018 at 10:51:55AM +0000, Suzuki K Poulose wrote: > On 07/02/18 10:43, Dave Martin wrote: > >On Thu, Feb 01, 2018 at 10:38:38AM +0000, Suzuki K Poulose wrote: > >>Expose the new features introduced by Arm v8.4 extensions to > >>Arm v8-A profile. > >> > >>These include : > >> > >> 1) Data indpendent timing of instructions. (DIT, exposed as HWCAP_DIT) > >> 2) Unaligned atomic instructions and Single-copy atomicity of loads > >> and stores. (AT, expose as HWCAP_USCAT) > >> 3) LDAPR and STLR instructions with immediate offsets (extension to > >> LRCPC, exposed as HWCAP_ILRCPC) > >> 4) Flag manipulation instructions (TS, exposed as HWCAP_FLAGM). > >> > >>While at it get rid of the RES0 entries in the cpu-feature-registers.txt > >>documentation. > > > >Should we write somewhere than fields that are not described here are > >implicitly RES0, or would that be too strong a statement? > > Dave, > > We already have the following description in the file : > > "The following rules are applied to the value returned by the > infrastructure: > > a) The value of an 'IMPLEMENTATION DEFINED' field is set to 0. > b) The value of a reserved field is populated with the reserved > value as defined by the architecture. > c) The value of a 'visible' field holds the system wide safe value > for the particular feature (except for MIDR_EL1, see section 4). > d) All other fields (i.e, invisible fields) are set to indicate > the feature is missing (as defined by the architecture). > " > > So we don't have to bother if the fields are RES0 or they get > some definitions in the future, as long as we don't expose them. Agreed, that does seem sufficient: Reviewed-by: Dave Martin [...] Cheers ---Dave