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=-8.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 E7B2AC433E7 for ; Tue, 13 Oct 2020 15:42:47 +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 9C421251F1 for ; Tue, 13 Oct 2020 15:42:47 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="xMeT4UsP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9C421251F1 Authentication-Results: mail.kernel.org; dmarc=fail (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-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject: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=kFLXCRh9gIJZbAGfzEraaL4HWBwKL2TAE7JZZYe8sXE=; b=xMeT4UsPYQFT+gyRz1MchkN1m f8QkCmKjcCu8bpmZVZ13/gnc9WBPPdoxbNqFs1WJx27OUDcTsSNSXNicmnOwCsJeYnIZzB/0JAp0g Vc7NujdgBp5TC3DhFyd0WZkbZ6JqWp7QiZxvdMkxkaQZiLtXFaPvwz+vrJonW0aFyQdonNCh4Ik8g 8sw2joLGtvNX1t9HKcMqouK7dcI0tMR1xDt4LuF+IiJv4w7AMYq9zCvzLyviFeu0Y7mvMzNZDcrlO IHHT3gwW9wJSS7CQ5Jcg8dKFQGhhapsPDzRf6LrhQtCU3eWt0HwIy2xWsGv5VlAyYkTgpi0ISvct4 PJppILdxQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kSMQI-0004rq-SQ; Tue, 13 Oct 2020 15:41:10 +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 1kSMQG-0004rR-9y for linux-arm-kernel@lists.infradead.org; Tue, 13 Oct 2020 15:41:09 +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 221D130E; Tue, 13 Oct 2020 08:41:07 -0700 (PDT) Received: from e121166-lin.cambridge.arm.com (e121166-lin.cambridge.arm.com [10.1.196.255]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 73F803F66B; Tue, 13 Oct 2020 08:41:05 -0700 (PDT) Date: Tue, 13 Oct 2020 16:41:00 +0100 From: Lorenzo Pieralisi To: Ard Biesheuvel Subject: Re: [PATCH] arm64: mm: set ZONE_DMA size based on early IORT scan Message-ID: <20201013154100.GA22293@e121166-lin.cambridge.arm.com> References: <20201010093153.30177-1-ardb@kernel.org> <20201013110929.GB20319@e121166-lin.cambridge.arm.com> <20201013131346.GA20925@e121166-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201013_114108_431832_431DE27C X-CRM114-Status: GOOD ( 42.27 ) 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: Anshuman Khandual , Catalin Marinas , Sudeep Holla , Robin Murphy , Jeremy Linton , ACPI Devel Maling List , Rob Herring , Linux ARM , Hanjun Guo , Will Deacon , Christoph Hellwig , Nicolas Saenz Julienne 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, Oct 13, 2020 at 03:42:07PM +0200, Ard Biesheuvel wrote: > On Tue, 13 Oct 2020 at 15:13, Lorenzo Pieralisi > wrote: > > > > On Tue, Oct 13, 2020 at 01:22:32PM +0200, Ard Biesheuvel wrote: > > > > [...] > > > > > > > diff --git a/Documentation/arm64/arm-acpi.rst b/Documentation/arm64/arm-acpi.rst > > > > > index 47ecb9930dde..947f5b5c45ef 100644 > > > > > --- a/Documentation/arm64/arm-acpi.rst > > > > > +++ b/Documentation/arm64/arm-acpi.rst > > > > > @@ -205,6 +205,13 @@ devices available. This list of tables is not meant to be all inclusive; > > > > > in some environments other tables may be needed (e.g., any of the APEI > > > > > tables from section 18) to support specific functionality. > > > > > > > > > > +It is assumed that all DMA capable devices in the system are able to > > > > > +access the lowest 4 GB of system memory. If this is not the case, an > > > > > +IORT describing those limitations is mandatory, even if an IORT is not > > > > > +otherwise necessary to describe the I/O topology, and regardless of > > > > > +whether _DMA methods are used to describe the DMA limitations more > > > > > +precisely. Once the system has booted, _DMA methods will take precedence > > > > > +over DMA addressing limits described in the IORT. > > > > > > > > If this is a boot requirement it must be in ARM's official documentation, > > > > first, not the kernel one. > > > > > > > > I understand this is an urgent (well - no comments on why bootstrapping > > > > ACPI on Raspberry PI4 is causing all this fuss, honestly) fix but that's > > > > not a reason to rush through these guidelines. > > > > > > > > I would not add this paragraph to arm-acpi.rst, yet. > > > > > > > > > > Which documentation? ACPI compliance by itself is not sufficient for a > > > system to be able to boot Linux/arm64, which is why we documented the > > > requirements for ACPI boot on Linux/arm64 in this file. I don't think > > > we need endorsement from ARM to decide that odd platforms like this > > > need to abide by some additional rules if they want to boot in ACPI > > > mode. > > > > I think we do - if we don't we should not add this documentation either. > > > > ACPI on ARM64 software stack is based on standardized HW requirements. > > The sheer fact that we need to work around a HW deficiency shows that > > either this platform should have never been booted with ACPI or the _HW_ > > design guidelines (BSA) are not tight enough. > > > > Please note that as you may have understood I asked if we can implement > > a workaround in IORT because that's information that must be there > > regardless (and an OEM ID match in arch code - though pragmatic - > > defeats the whole purpose), I don't think we should tell Linux kernel > > developers how firmware must be written to work around blatantly > > non-compliant systems. > > > > This is not about systems being compliant or not, unless there is a > requirement somewhere that I missed that all masters in the system > must be able to access at least 32 bits of DMA. I think there is in the SBSA (4.1.3 Memory Map) but regardless, this is clearly a design bug, that's not a feature. > The problem here is that Linux/arm64 cannot deal with fully compliant > systems that communicate their [permitted] DMA limitations via a _DMA > method if this limitation happens to be that the address limit < 32 > bits. The DMA subsystem can deal with this fine, only the default DMA > zone sizing policy creates an internal issue where the DMA subsystem > is not able to allocate memory that matches the DMA constraints. > > So the 'correct' fix here would be to rework the memory allocator so > it can deal with arbitrary DMA limits at allocation time, so that any > limit returned by a _DMA method can be adhered to on the fly. > > However, we all agree that the Raspberry Pi4 is not worth that effort, > and that in the general case, SoCs with such limitations, even if they > are compliant per the spec, are not worth the trouble of complicating > this even more. So as a compromise, I think it is perfectly reasonable > to require that systems that have such limitations communicate them > via the IORT, which we can parse early, regardless of whether _DMA > methods exist as well, and whether they return the same information. > > So this is not a requirement on arm64 ACPI systems in general. It is a > requirement that expresses that we, as arm64 > contributors/[co-]maintainers, are willing to cater for such systems > if they implement their firmware in a particular way. I don't think they should implement their firmware in any particular way, that's my point, I don't want them to in the first place. To start with there is no spec I am aware of that defines when/how to use _DMA vs IORT address limits, maybe we should spell that out better somewhere and that's useful regardless. My point is: either this workaround works with firmware written with guidelines valid for all arm64 systems (not as a special case: add an IORT table because we can't parse _DMA to workaround DMA address range shenanigans) or I am not willing to merge it - I prefer to add an OEM ID quirk and show what we are forced to do to make this work. Thanks, Lorenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel