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 0F9FBC433F5 for ; Thu, 28 Apr 2022 09:20:39 +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=lk40gXJ9lz3dLZi23vPbtiQNrAQluMpsuB19VN21Xqg=; b=UEXiKNcYnVN7Rf 9p1etSFyUs9gtH95z+pwotaOfNw0KJ9cT3MfcktLoHnivoGfJ4YPEdameEiVHckPGX8t8v1+6gam8 ZdqlaLvaAFxzcQ5H6E6v+n/tD75PqNWjJ7B3/1oLw5Zp1lL3jHr5mguIWFZwgZmHr1Yqz+vFrOHRH wEam8m3dKoDqNWEkITgftb4vL7CnQb9Lskz7AWGuOfeGzMd+MMGpTWz1CJjG5B8CVDn4TKmzahEjn VswaQawy9GgNeQmpXwn3QzrUVQnAT/kbQxUFDV/knogZWW1B+FnFUr0clCIMg9P2nGJGteCuhRa6E /9yzLxb/Pu6TXlA6VZtQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1nk0JB-005fPW-MS; Thu, 28 Apr 2022 09:19:33 +0000 Received: from dfw.source.kernel.org ([2604:1380:4641:c500::1]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1nk0J8-005fOE-Pb for linux-arm-kernel@lists.infradead.org; Thu, 28 Apr 2022 09:19:32 +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 dfw.source.kernel.org (Postfix) with ESMTPS id 4F58E612C5; Thu, 28 Apr 2022 09:19:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 700BEC385A0; Thu, 28 Apr 2022 09:19:26 +0000 (UTC) Date: Thu, 28 Apr 2022 10:19:22 +0100 From: Catalin Marinas To: Mark Brown Cc: Will Deacon , Marc Zyngier , Shuah Khan , Shuah Khan , Alan Hayward , Luis Machado , Salil Akerkar , Basant Kumar Dwivedi , Szabolcs Nagy , James Morse , Alexandru Elisei , Suzuki K Poulose , Luca Salabrino , linux-arm-kernel@lists.infradead.org, linux-kselftest@vger.kernel.org, kvmarm@lists.cs.columbia.edu Subject: Re: [PATCH v14 04/39] arm64/sme: Provide ABI documentation for SME Message-ID: References: <20220419112247.711548-1-broonie@kernel.org> <20220419112247.711548-5-broonie@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20220419112247.711548-5-broonie@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220428_021930_906377_CC7DC6A7 X-CRM114-Status: GOOD ( 13.04 ) 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 Tue, Apr 19, 2022 at 12:22:12PM +0100, Mark Brown wrote: > +* There are a number of optional SME features, presence of these is reported > + through AT_HWCAP2 through: > + > + HWCAP2_SME_I16I64 > + HWCAP2_SME_F64F64 > + HWCAP2_SME_I8I32 > + HWCAP2_SME_F16F32 > + HWCAP2_SME_B16F32 > + HWCAP2_SME_F32F32 > + HWCAP2_SME_FA64 Marc pointed out that in combination with FEAT_WFxT, we used all the HWCAP2 bits (32). While we are ok for now, we'll soon need to look into what to do when the next features turn up. Some options: 1. Only provide HWCAP2_SME and let the ID_AA64SMFR0_EL1 features be probed via MRS emulation. It doesn't solve the problem but it buys us a bit of time. 2. Don't bother with any new HWCAPs, just rely on MRS emulation (we have HWCAP_CPUID advertising this). 3. Start using the upper 32-bit of HWCAP and HWCAP2 (we initially didn't go into these as there was a slight chance of merging ILP32). Does the libc rely on the upper bits for anything? Or does it just assume a 32-bit HWCAPs layout? 4. Introduce HWCAP3. Szabolcs, any thoughts? Thanks. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel