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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 8F730C43467 for ; Fri, 16 Oct 2020 07:27:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 442122073A for ; Fri, 16 Oct 2020 07:27:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404561AbgJPH1c (ORCPT ); Fri, 16 Oct 2020 03:27:32 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:15303 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2404514AbgJPH1c (ORCPT ); Fri, 16 Oct 2020 03:27:32 -0400 Received: from DGGEMS403-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 1BF5547CB1A9DC141914; Fri, 16 Oct 2020 15:27:29 +0800 (CST) Received: from [10.174.179.182] (10.174.179.182) by DGGEMS403-HUB.china.huawei.com (10.3.19.203) with Microsoft SMTP Server id 14.3.487.0; Fri, 16 Oct 2020 15:27:22 +0800 Subject: Re: [PATCH v3 7/8] arm64: mm: Set ZONE_DMA size based on early IORT scan To: Ard Biesheuvel CC: Catalin Marinas , Nicolas Saenz Julienne , Rob Herring , Christoph Hellwig , Linux Kernel Mailing List , Lorenzo Pieralisi , Sudeep Holla , Robin Murphy , Linux ARM , "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" , Jeremy Linton , Linux IOMMU , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Anshuman Khandual , Will Deacon , "Rafael J. Wysocki" , "Len Brown" , ACPI Devel Maling List , Linuxarm References: <20201014191211.27029-1-nsaenzjulienne@suse.de> <20201014191211.27029-8-nsaenzjulienne@suse.de> <1a3df60a-4568-cb72-db62-36127d0ffb7e@huawei.com> <20201015180340.GB2624@gaia> <35faab1c-5c32-6cd3-0a14-77057dd223f5@huawei.com> From: Hanjun Guo Message-ID: <89ed58a5-b3ca-e361-94d8-b6754ce5eb34@huawei.com> Date: Fri, 16 Oct 2020 15:27:21 +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: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.182] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org Hi Ard, On 2020/10/16 14:54, Ard Biesheuvel wrote: > On Fri, 16 Oct 2020 at 08:51, Hanjun Guo wrote: >> >> 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. >> > > Hello Hanjun, > > The patch only takes the address limit field into account if its value > 0. Sorry I missed the if (*->memory_address_limit) check, thanks for the reminding. > > Also, before commit 7fb89e1d44cb6aec ("ACPI/IORT: take _DMA methods > into account for named components"), the _DMA method was not taken > into account for named components at all, and only the IORT limit was > used, so I do not anticipate any problems with that. Then this patch is fine to me. Thanks Hanjun