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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 13EF5C433EF for ; Mon, 21 Feb 2022 19:05:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=CGE1ZSH0VJp8RqiYTa+0WNgb0bRHFzF1+g7Nl6aC2X4=; b=cJ2BqWxhziZPOx LtXXEG3drXEuD+3sST74QbycuNi92MBEEhszjiYhXPact4hN2GMB2a9IqyLBSL+2xbMV+FtY+MoG0 8neCGzAabcdOZAuiAQkVnZTRtmmelsF6dMDJKW+YXQHijqagSM4I+rpTtewmL2aOB7sVbpZcimFbd f3vYNEZORgMK1JGs6R+7hNCWPXmPhSmkQ1NsKaqWRhuyfNdJ5NrDF4nvjJXcOdO5h2jAR++6n/+O3 MUrvwVDK/uTVbzQmm+6qxleoCtBzFcdyiW/G4t07kcO4a42xYSalzwFnsmzig9kIH7jIQyoKDLiKP iBLQsgE+2KgY195HteIA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nMDzH-0072Y9-IX; Mon, 21 Feb 2022 19:04:43 +0000 Received: from ams.source.kernel.org ([2604:1380:4601:e00::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nMDzE-0072XH-6n for linux-arm-kernel@lists.infradead.org; Mon, 21 Feb 2022 19:04:41 +0000 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id D9609B8110A; Mon, 21 Feb 2022 19:04:38 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C3CF7C340E9; Mon, 21 Feb 2022 19:04:34 +0000 (UTC) Date: Mon, 21 Feb 2022 19:04:31 +0000 From: Catalin Marinas To: Szabolcs Nagy Cc: Mark Brown , Will Deacon , Marc Zyngier , Shuah Khan , Shuah Khan , Alan Hayward , Luis Machado , Salil Akerkar , Basant Kumar Dwivedi , James Morse , Alexandru Elisei , Suzuki K Poulose , linux-arm-kernel@lists.infradead.org, linux-kselftest@vger.kernel.org, kvmarm@lists.cs.columbia.edu Subject: Re: [PATCH v11 10/40] arm64/sme: Basic enumeration support Message-ID: References: <20220207152109.197566-1-broonie@kernel.org> <20220207152109.197566-11-broonie@kernel.org> <20220221160706.GK2692478@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220221160706.GK2692478@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220221_110440_551743_4B5F5936 X-CRM114-Status: GOOD ( 22.64 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Feb 21, 2022 at 04:07:06PM +0000, Szabolcs Nagy wrote: > The 02/21/2022 14:32, Catalin Marinas wrote: > > On Mon, Feb 07, 2022 at 03:20:39PM +0000, Mark Brown wrote: > > > diff --git a/Documentation/arm64/elf_hwcaps.rst b/Documentation/arm64/elf_hwcaps.rst > > > index b72ff17d600a..5626cf208000 100644 > > > --- a/Documentation/arm64/elf_hwcaps.rst > > > +++ b/Documentation/arm64/elf_hwcaps.rst > > > @@ -259,6 +259,39 @@ HWCAP2_RPRES > > > > > > Functionality implied by ID_AA64ISAR2_EL1.RPRES == 0b0001. > > > > > > +HWCAP2_SME > > > + > > > + Functionality implied by ID_AA64PFR1_EL1.SME == 0b0001, as described > > > + by Documentation/arm64/sme.rst. > > > + > > > +HWCAP2_SME_I16I64 > > > + > > > + Functionality implied by ID_AA64SMFR0_EL1.I16I64 == 0b1111. > > > + > > > +HWCAP2_SME_F64F64 > > > + > > > + Functionality implied by ID_AA64SMFR0_EL1.F64F64 == 0b1. > > > + > > > +HWCAP2_SME_I8I32 > > > + > > > + Functionality implied by ID_AA64SMFR0_EL1.I8I32 == 0b1111. > > > + > > > +HWCAP2_SME_F16F32 > > > + > > > + Functionality implied by ID_AA64SMFR0_EL1.F16F32 == 0b1. > > > + > > > +HWCAP2_SME_B16F32 > > > + > > > + Functionality implied by ID_AA64SMFR0_EL1.B16F32 == 0b1. > > > + > > > +HWCAP2_SME_F32F32 > > > + > > > + Functionality implied by ID_AA64SMFR0_EL1.F32F32 == 0b1. > > > + > > > +HWCAP2_SME_FA64 > > > + > > > + Functionality implied by ID_AA64SMFR0_EL1.FA64 == 0b1. > > > > More of a question for the libc people: should we drop the fine-grained > > HWCAP corresponding to the new ID_AA64SMFR0_EL1 register (only keep > > HWCAP2_SME) and get the user space to use the MRS emulation? Would any > > ifunc resolver be affected? > > good question. > > within glibc HWCAP2_SME is enough (to decide if we need to > deal with additional register state and the lazy ZA save > scheme) but i guess user code that actually uses sme would > need the details (including in ifunc resolvers in principle). > > since we have mrs, there is no strict need for hwcaps. > if ifunc resolvers using this info are not widespread then > the mrs emulation overhead is acceptable, but i suspect > hwcaps are nicer to use. I presume the ifunc resolvers only run once, so the overhead won't be noticed. Anyway, happy to keep the new HWCAP2 if they are useful. > do we have a plan after hwcap2 bits run out? :) HWCAP3 or we free up the top 32-bit in both HWCAP and HWCAP2 ranges. We did not extend into those upper bits because of the ILP32 discussions at the time. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel