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=-8.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 D9240C433E7 for ; Tue, 13 Oct 2020 15:12:56 +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 6E6C0248FB for ; Tue, 13 Oct 2020 15:12:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="oU+rzgiL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6E6C0248FB 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-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=Dy0tBLH1MrpeYr4F835kwB7irMdlGMGdIjl3n0gu4rc=; b=oU+rzgiLmRjRirCpQxQef+6+v FKXPoIemdrneMHWR8NXvU+Rqy5VpNXTPn+yBnogrwbm4z4/o00LhjjomUGky+1qoXEsh4gwoAv6XW qIJCWDKhLJbZJuDcOr4HG7PBNwhjRD+BmGZtgLOUQbNfV6/rixVtYsYh25Jyf+xWfIlFVT02YiKnf SYpFSWkdScaIdaok98zL1LiQfa6/gSSb8uq53uhTNotuwx8PIc2DfnzeBAspebUQ0GIZqw5ePDWWv a1jzYPt8AEeYSoJpbSf6LIwqpBItFwuyotaPkmRpxQDZLQ4h6W0+bz/dPylDGGg7uhMirAnBOuEBa bJf8/jndQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kSLxY-0001KK-4L; Tue, 13 Oct 2020 15:11:28 +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 1kSLxU-0001JX-8Q for linux-arm-kernel@lists.infradead.org; Tue, 13 Oct 2020 15:11:25 +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 B5859106F; Tue, 13 Oct 2020 08:11:21 -0700 (PDT) Received: from [10.57.48.76] (unknown [10.57.48.76]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AD2373F66B; Tue, 13 Oct 2020 08:11:19 -0700 (PDT) Subject: Re: [PATCH] arm64: mm: set ZONE_DMA size based on early IORT scan To: Ard Biesheuvel , Lorenzo Pieralisi References: <20201010093153.30177-1-ardb@kernel.org> <20201013110929.GB20319@e121166-lin.cambridge.arm.com> <20201013131346.GA20925@e121166-lin.cambridge.arm.com> From: Robin Murphy Message-ID: <4d1a4577-0394-005a-d5bc-cfadb39f776d@arm.com> Date: Tue, 13 Oct 2020 16:11:18 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.3.2 MIME-Version: 1.0 In-Reply-To: Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201013_111124_450440_B4E07315 X-CRM114-Status: GOOD ( 33.46 ) 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 , Jeremy Linton , ACPI Devel Maling List , Rob Herring , Linux ARM , Hanjun Guo , Will Deacon , Christoph Hellwig , Nicolas Saenz Julienne 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 2020-10-13 14:42, 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. > > 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. Yup, it's a shame that [1] apparently never got anywhere. I believe that killing off the DMA zones is still something we'd like to work towards (or at least I hope it is...) but I doubt we're going to get there very soon. Robin. [1] https://lore.kernel.org/lkml/200803071007.493903088@firstfloor.org/ > 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. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel