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=-10.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 ABC12C4363A for ; Fri, 16 Oct 2020 06:52:55 +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 1747A207C4 for ; Fri, 16 Oct 2020 06:52:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Ve+D7ga1" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1747A207C4 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.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=l2QXR9RfMcgtlfuhygnSVWd8K1vB4P29KIQoQ4C0tgs=; b=Ve+D7ga1i7oIdfuqs7dTBEaPJ VXfDuQZp9GfPlm4yMib4hv+vDr/CEcyTL7xdIDEYsRqMwS//5joQvYUhunoTnQMnPWsD4lnKmNBC4 9v74LH/nMUouCRJzSedhQon8D9SrrJqyD5dIY+b0cyyXYSymxSXgJA1H3nH6DjPcq2VQhWm7UM2dr LZ/avhE9CDIFQ/wziuY+KBiKrUucBFXI7FeoYK7xoGkXuTOHPWtDRACewNvNYZrdlQt3WbtLkE5/I HZZTUhNVx58Q8Lpn9OKpOFxu0Gi03XkRtsSVX3zSD5IUIX1CS2jsxBbSPielV4ghT197+9BKTXMGC 4CT2i2p/w==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kTJaL-0001Ng-Tc; Fri, 16 Oct 2020 06:51:29 +0000 Received: from szxga04-in.huawei.com ([45.249.212.190] helo=huawei.com) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kTJaH-0001Ml-BF; Fri, 16 Oct 2020 06:51:27 +0000 Received: from DGGEMS413-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 419B7DF0B12213270867; Fri, 16 Oct 2020 14:51:17 +0800 (CST) Received: from [10.174.179.182] (10.174.179.182) by DGGEMS413-HUB.china.huawei.com (10.3.19.213) with Microsoft SMTP Server id 14.3.487.0; Fri, 16 Oct 2020 14:51:09 +0800 Subject: Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan To: Catalin Marinas References: <20201014191211.27029-1-nsaenzjulienne@suse.de> <20201014191211.27029-8-nsaenzjulienne@suse.de> <1a3df60a-4568-cb72-db62-36127d0ffb7e@huawei.com> <20201015180340.GB2624@gaia> From: Hanjun Guo Message-ID: <35faab1c-5c32-6cd3-0a14-77057dd223f5@huawei.com> Date: Fri, 16 Oct 2020 14:51:09 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20201015180340.GB2624@gaia> Content-Language: en-GB X-Originating-IP: [10.174.179.182] X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201016_025126_196356_E9461BC1 X-CRM114-Status: GOOD ( 17.56 ) 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: devicetree@vger.kernel.org, Lorenzo Pieralisi , Anshuman Khandual , Will Deacon , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, jeremy.linton@arm.com, ardb@kernel.org, linux-acpi@vger.kernel.org, iommu@lists.linux-foundation.org, robh+dt@kernel.org, Linuxarm , linux-arm-kernel@lists.infradead.org, Sudeep Holla , Len Brown , robin.murphy@arm.com, hch@lst.de, Nicolas Saenz Julienne , linux-rpi-kernel@lists.infradead.org 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 2020/10/16 2:03, Catalin Marinas wrote: > On Thu, Oct 15, 2020 at 10:26:18PM +0800, Hanjun Guo wrote: >> On 2020/10/15 3:12, Nicolas Saenz Julienne wrote: >>> From: Ard Biesheuvel >>> >>> We recently introduced a 1 GB sized ZONE_DMA to cater for platforms >>> incorporating masters that can address less than 32 bits of DMA, in >>> particular the Raspberry Pi 4, which has 4 or 8 GB of DRAM, but has >>> peripherals that can only address up to 1 GB (and its PCIe host >>> bridge can only access the bottom 3 GB) >>> >>> Instructing the DMA layer about these limitations is straight-forward, >>> even though we had to fix some issues regarding memory limits set in >>> the IORT for named components, and regarding the handling of ACPI _DMA >>> methods. However, the DMA layer also needs to be able to allocate >>> memory that is guaranteed to meet those DMA constraints, for bounce >>> buffering as well as allocating the backing for consistent mappings. >>> >>> This is why the 1 GB ZONE_DMA was introduced recently. Unfortunately, >>> it turns out the having a 1 GB ZONE_DMA as well as a ZONE_DMA32 causes >>> problems with kdump, and potentially in other places where allocations >>> cannot cross zone boundaries. Therefore, we should avoid having two >>> separate DMA zones when possible. >>> >>> So let's do an early scan of the IORT, and only create the ZONE_DMA >>> if we encounter any devices that need it. This puts the burden on >>> the firmware to describe such limitations in the IORT, which may be >>> redundant (and less precise) if _DMA methods are also being provided. >>> However, it should be noted that this situation is highly unusual for >>> arm64 ACPI machines. Also, the DMA subsystem still gives precedence to >>> the _DMA method if implemented, and so we will not lose the ability to >>> perform streaming DMA outside the ZONE_DMA if the _DMA method permits >>> it. >> >> Sorry, I'm still a little bit confused. With this patch, if we have >> a device which set the right _DMA method (DMA size >= 32), but with the >> wrong DMA size in IORT, we still have the ZONE_DMA created which >> is actually not needed? > > With the current kernel, we get a ZONE_DMA already with an arbitrary > size of 1GB that matches what RPi4 needs. We are trying to eliminate > such unnecessary ZONE_DMA based on some heuristics (well, something that > looks "better" than a OEM ID based quirk). Now, if we learn that IORT > for platforms in the field is that broken as to describe few bits-wide > DMA masks, we may have to go back to the OEM ID quirk. Some platforms using 0 as the memory size limit, for example D05 [0] and D06 [1], I think we need to go back to the OEM ID quirk. For D05/D06, there are multi interrupt controllers named as mbigen, mbigen is using the named component to describe the mappings with the ITS controller, and mbigen is using 0 as the memory size limit. Also since the memory size limit for PCI RC was introduced by later IORT revision, so firmware people may think it's fine to set that as 0 because the system works without it. Thanks Hanjun [0]: https://github.com/tianocore/edk2-platforms/blob/master/Silicon/Hisilicon/Hi1616/D05AcpiTables/D05Iort.asl [1]: https://github.com/tianocore/edk2-platforms/blob/master/Silicon/Hisilicon/Hi1620/Hi1620AcpiTables/Hi1620Iort.asl _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel