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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,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 7E02FC19F35 for ; Mon, 9 Aug 2021 19:48:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 632FB60C51 for ; Mon, 9 Aug 2021 19:48:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236193AbhHITsz (ORCPT ); Mon, 9 Aug 2021 15:48:55 -0400 Received: from foss.arm.com ([217.140.110.172]:39836 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236164AbhHITsk (ORCPT ); Mon, 9 Aug 2021 15:48:40 -0400 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 AB65CD6E; Mon, 9 Aug 2021 12:48:18 -0700 (PDT) Received: from [192.168.122.166] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 29FC53F40C; Mon, 9 Aug 2021 12:48:18 -0700 (PDT) Subject: Re: [PATCH 2/3] PCI: brcmstb: Add ACPI config space quirk To: Bjorn Helgaas Cc: linux-pci@vger.kernel.org, lorenzo.pieralisi@arm.com, nsaenz@kernel.org, bhelgaas@google.com, rjw@rjwysocki.net, lenb@kernel.org, robh@kernel.org, kw@linux.com, f.fainelli@gmail.com, bcm-kernel-feedback-list@broadcom.com, linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rpi-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <20210809174244.GA2167737@bjorn-Precision-5520> From: Jeremy Linton Message-ID: <4d4732b9-e8df-3803-2db7-c6eef1196269@arm.com> Date: Mon, 9 Aug 2021 14:48:17 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <20210809174244.GA2167737@bjorn-Precision-5520> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 8/9/21 12:42 PM, Bjorn Helgaas wrote: > On Fri, Aug 06, 2021 at 09:55:27PM -0500, Jeremy Linton wrote: >> Hi, >> >> On 8/6/21 5:21 PM, Bjorn Helgaas wrote: >>> On Thu, Aug 05, 2021 at 04:11:59PM -0500, Jeremy Linton wrote: >>>> The PFTF CM4 is an ACPI platform that is following the PCIe SMCCC >>>> standard because its PCIe config space isn't ECAM compliant and is >>>> split into two parts. One part for the root port registers and a >>>> moveable window which points at a given device's 4K config space. >>>> Thus it doesn't have a MCFG (and really any MCFG provided would be >>>> nonsense anyway). As Linux doesn't support the PCIe SMCCC standard >>>> we key off a Linux specific host bridge _DSD to add custom ECAM >>>> ops and cfgres. The cfg op selects between those two regions, as >>>> well as disallowing problematic accesses, particularly if the link >>>> is down because there isn't an attached device. >>> >>> I'm not sure SMCCC is *really* relevant here. If it is, an expansion >>> of the acronym and a link to a spec would be helpful. >>> >>> But AFAICT the only important thing here is that it doesn't have >>> standard ECAM, and we're going to work around that. >> >> I will reword it a bit. >> >>> I don't see anything about _DSD in this series. >> >> That is the "linux,pci-quirk" in the next patch. > > The next patch doesn't mention _DSD either. Is it obfuscated by > being inside fwnode_property_read_string()? If so, it's well and > truly hidden; I gave up trying to connect that with ACPI. Right, the fwnode stuff works as a DT/ACPI abstraction for reading values from firmware tables. In this case the ACPI definition looks something like: Device(PCI0) { ... Name (_DSD, Package () { ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"), Package () { Package () { "linux-pcie-quirk", "bcm2711" }, } }) ... } Which explains a bit of why the underlying code is a bit uh... complicated.