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=-8.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SIGNED_OFF_BY, 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 4AB1CC43467 for ; Fri, 16 Oct 2020 07:07:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 057CF20720 for ; Fri, 16 Oct 2020 07:07:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2394508AbgJPHHH (ORCPT ); Fri, 16 Oct 2020 03:07:07 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:15227 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2394401AbgJPHHH (ORCPT ); Fri, 16 Oct 2020 03:07:07 -0400 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 588DA7865FCC9F27216E; Fri, 16 Oct 2020 15:07:04 +0800 (CST) Received: from [127.0.0.1] (10.174.177.134) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.487.0; Fri, 16 Oct 2020 15:06:59 +0800 Subject: Re: [PATCH 1/2] arm64: dts: broadcom: remove an unused property dma-ranges To: Arnd Bergmann CC: devicetree , Florian Fainelli , Scott Branden , Ray Jui , linux-kernel , Rob Herring , Bjorn Andersson , "Andy Gross" , bcm-kernel-feedback-list , linux-arm-msm , linux-arm-kernel References: <20201013060623.1711-1-thunder.leizhen@huawei.com> <20201013060623.1711-2-thunder.leizhen@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <989f3efa-4fd0-8061-266c-56de03ce9029@huawei.com> Date: Fri, 16 Oct 2020 15:06:57 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.134] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On 2020/10/14 22:02, Arnd Bergmann wrote: > On Wed, Oct 14, 2020 at 3:36 PM Leizhen (ThunderTown) > wrote: >> On 2020/10/14 15:38, Arnd Bergmann wrote: >>> On Wed, Oct 14, 2020 at 5:15 AM Florian Fainelli wrote: >>>> On 10/12/2020 11:06 PM, Zhen Lei wrote: >>>>> stingray-usb.dtsi is finally included by three dts files: >>>>> bcm958802a802x.dts, bcm958742k.dts and bcm958742t.dts. I searched all >>>>> these three entire expanded dts files, and each of them contains only one >>>>> dma-ranges. No conversion range is specified, so it cannot work properly. >>>>> I think this property "dma-ranges" is added by mistake, just remove it. >>>>> Otherwise, the following error will be reported when any YAML detection >>>>> is performed on arm64. >>>>> >>>>> arch/arm64/boot/dts/broadcom/stingray/stingray-usb.dtsi:7.3-14: Warning \ >>>>> (dma_ranges_format): /usb:dma-ranges: empty "dma-ranges" property but \ >>>>> its #address-cells (1) differs from / (2) >>>>> arch/arm64/boot/dts/broadcom/stingray/stingray-usb.dtsi:7.3-14: Warning \ >>>>> (dma_ranges_format): /usb:dma-ranges: empty "dma-ranges" property but \ >>>>> its #size-cells (1) differs from / (2) >>>>> >>>>> Signed-off-by: Zhen Lei >>>> >>>> This looks fine to me, Scott, Ray do you want to Ack this patch before I >>>> take it? >>> >>> Does it mean that there are no devices on this bus that can do DMA? >>> >>> Usually there should be a dma-ranges property to identify that DMA >>> is possible and what the limits are, though we have failed to enforce >>> that. >> >> Documentation/devicetree/bindings/iommu/iommu.txt +79 >> When an "iommus" property is specified in a device tree node, the IOMMU will >> be used for address translation. If a "dma-ranges" property exists in the >> device's parent node it will be ignored. An exception to this rule is if the >> referenced IOMMU is disabled, in which case the "dma-ranges" property of the >> parent shall take effect. >> >> The dma-ranges is only required by IOMMU disabled case. And should exist in >> the parent node of IOMMU device. But this deleted dma-ranges is under the usb >> bus node. > > The USB hosts here don't use an IOMMU though, right? Generally, USB devices are accessed through the IOMMU. However, even in this case, dma-ranges is not necessarily required. There are many examples of this in arch/arm64/boot/dts/. For example: arch/arm64/boot/dts/arm/juno.dt.yaml. Not sure, but maybe I found the answer. vi drivers/of/address.c +457 457 Thus we treat the absence of 458 * "ranges" as equivalent to an empty "ranges" property which means 459 * a 1:1 translation at that level. 466 * This quirk also applies for 'dma-ranges' which frequently exist in 467 * child nodes without 'dma-ranges' in the parent nodes. --RobH 475 if (ranges == NULL || rlen == 0) { 476 offset = of_read_number(addr, na); 477 memset(addr, 0, pna * 4); 478 pr_debug("empty ranges; 1:1 translation\n"); 479 goto finish; 480 } By the way: At first, I thought that these errors was detected by YAML. Now, I found that it was generated by "make dtbs". That's why it was reported by any YAML. Thus, the need to fix these errors is even more urgent. > >>> Also note that the #address-cells=<1> means that any device under >>> this bus is assumed to only support 32-bit addressing, and DMA will >>> have to go through a slow swiotlb in the absence of an IOMMU. >> >> The dma_alloc_coherent() will allocate memory with GFP_DMA32 flag and >> try the 0-4G first. The reserved swiotlb buffer memory is used only >> when the allocation failed. > > The swiotlb is primarily about the streaming mappings with dma_map_*(), > which has to copy all data sent to the device. dma_alloc_coherent() > is a rare operation and less impacted by DMA limitations. OK, I got it. > > Arnd > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel > > . >