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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 D0775C433E0 for ; Wed, 1 Jul 2020 19:04:40 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8FEE22082F for ; Wed, 1 Jul 2020 19:04:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="n3YPxAYj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8FEE22082F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=a1cle1M3eicJnsVTO0Oh+OPK7MBcfJYPQSCB08j4PyE=; b=n3YPxAYjHprQMnl1kwoAxbYO7 Ke1ClbHayTQV4yUmZTtKUQ08GTYwKNY0ZPuRifIiK5Tj6zOMl44NE3H/K6C0nzHNDhTfNYS6nVOs8 4p3wixRUih1V8EOnFhqZelrvxj+4i7GgBVCfbXDa37/+O7TDoqwUepzxDWEGMEGC7xuAF0jzsahET eFO/QcnbnD3/WJdSn807uyfw3ky/3vjTquzz9e6J9sEokbc8VNshcQS4wICTG1A7IKDVxRUH7hp6+ 3PGdhg90p06SoxJLTx6Jkl9doSE1mhUq6ZJgTXO6FToqHkh/VNhIcm3nchJqeC6bazEJF2EBfz4nM ZouGKtDng==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqi0t-0003a8-K9; Wed, 01 Jul 2020 19:03:19 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jqi0q-0003ZQ-7k for linux-arm-kernel@lists.infradead.org; Wed, 01 Jul 2020 19:03:17 +0000 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 BA3441FB; Wed, 1 Jul 2020 12:03:14 -0700 (PDT) Received: from [10.57.21.32] (unknown [10.57.21.32]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id E0A843F68F; Wed, 1 Jul 2020 12:03:11 -0700 (PDT) Subject: Re: [PATCH v8 2/3] dt-bindings: arm-smmu: Add binding for Tegra194 SMMU To: Jon Hunter , Krishna Reddy References: <20200630001051.12350-1-vdumpa@nvidia.com> <20200630001051.12350-3-vdumpa@nvidia.com> <3e655881-bac4-f083-44ed-cfa0a61298d0@arm.com> <0d4f46d6-6a4e-bca0-bcf3-0e22a950e57b@nvidia.com> From: Robin Murphy Message-ID: Date: Wed, 1 Jul 2020 20:03:10 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <0d4f46d6-6a4e-bca0-bcf3-0e22a950e57b@nvidia.com> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200701_150316_357645_9FF10AA5 X-CRM114-Status: GOOD ( 18.73 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Sachin Nikam , "nicoleotsuka@gmail.com" , Mikko Perttunen , Bryan Huntsman , "joro@8bytes.org" , "linux-kernel@vger.kernel.org" , Pritesh Raithatha , Timo Alho , "iommu@lists.linux-foundation.org" , Nicolin Chen , "linux-tegra@vger.kernel.org" , Yu-Huan Hsu , Thierry Reding , "will@kernel.org" , "linux-arm-kernel@lists.infradead.org" , Bitan Biswas Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-07-01 19:47, Jon Hunter wrote: > > On 01/07/2020 19:28, Krishna Reddy wrote: >>>> + - description: NVIDIA SoCs that use more than one "arm,mmu-500" >>> Hmm, there must be a better way to word that to express that it only applies to the sets of SMMUs that must be programmed identically, and not any other independent MMU-500s that might also happen to be in the same SoC. >> >> Let me reword it to "NVIDIA SoCs that must program multiple MMU-500s identically". >> >>>> + items: >>>> + - enum: >>>> + - nvdia,tegra194-smmu >>>> + - const: arm,mmu-500 >> >>> Is the fallback compatible appropriate here? If software treats this as a standard MMU-500 it will only program the first instance (because the second isn't presented as a separate MMU-500) - is there any way that isn't going to blow up? >> >> When compatible is set to both nvidia,tegra194-smmu and arm,mmu-500, implementation override ensure that both instances are programmed. Isn't it? I am not sure I follow your comment fully. > > The problem is, if for some reason someone had a Tegra194, but only set > the compatible string to 'arm,mmu-500' it would assume that it was a > normal arm,mmu-500 and only one instance would be programmed. We always > want at least 2 of the 3 instances programmed and so we should only > match 'nvidia,tegra194-smmu'. In fact, I think that we also need to > update the arm_smmu_of_match table to add 'nvidia,tegra194-smmu' with > the data set to &arm_mmu500. Right, the main concern is if the shiny new DT gets passed to an older kernel (or other OS entirely) which doesn't know the "nvdia,tegra194-smmu" compatible but would match on "arm,mmu-500" and bind a standard driver thinking it's going to work OK. The user would probably prefer that no driver matched and both instances were left turned off, than face the fallout of only one of them being set up. Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel