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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 BAEA4C433E2 for ; Tue, 23 Mar 2021 18:10:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 745E7619C2 for ; Tue, 23 Mar 2021 18:10:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231577AbhCWSKI (ORCPT ); Tue, 23 Mar 2021 14:10:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:43370 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231243AbhCWSJk (ORCPT ); Tue, 23 Mar 2021 14:09:40 -0400 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9F0F36192B; Tue, 23 Mar 2021 18:09:39 +0000 (UTC) Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94) (envelope-from ) id 1lOlTF-003MZw-KT; Tue, 23 Mar 2021 18:09:37 +0000 Date: Tue, 23 Mar 2021 18:09:36 +0000 Message-ID: <87im5hkahr.wl-maz@kernel.org> From: Marc Zyngier To: Robin Murphy Cc: Lorenzo Pieralisi , Bjorn Helgaas , Frank Wunderlich , Thierry Reding , Thomas Gleixner , Rob Herring , Will Deacon , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Michael Kelley , Wei Liu , Thierry Reding , Jonathan Hunter , Ryder Lee , Marek Vasut , Yoshihiro Shimoda , Michal Simek , Paul Walmsley , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-hyperv@vger.kernel.org, linux-tegra@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-renesas-soc@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH v2 12/15] PCI/MSI: Let PCI host bridges declare their reliance on MSI domains In-Reply-To: <6a2eaa5d-1d83-159f-69e5-c9e0a00a7b50@arm.com> References: <20210322184614.802565-1-maz@kernel.org> <20210322184614.802565-13-maz@kernel.org> <6a2eaa5d-1d83-159f-69e5-c9e0a00a7b50@arm.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: robin.murphy@arm.com, lorenzo.pieralisi@arm.com, bhelgaas@google.com, frank-w@public-files.de, treding@nvidia.com, tglx@linutronix.de, robh@kernel.org, will@kernel.org, kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, mikelley@microsoft.com, wei.liu@kernel.org, thierry.reding@gmail.com, jonathanh@nvidia.com, ryder.lee@mediatek.com, marek.vasut+renesas@gmail.com, yoshihiro.shimoda.uh@renesas.com, michal.simek@xilinx.com, paul.walmsley@sifive.com, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-hyperv@vger.kernel.org, linux-tegra@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-renesas-soc@vger.kernel.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org Hi Robin, On Tue, 23 Mar 2021 11:45:02 +0000, Robin Murphy wrote: > > On 2021-03-22 18:46, Marc Zyngier wrote: > > The new 'no_msi' attribute solves the problem of advertising the lack > > of MSI capability for host bridges that know for sure that there will > > be no MSI for their end-points. > > > > However, there is a whole class of host bridges that cannot know > > whether MSIs will be provided or not, as they rely on other blocks > > to provide the MSI functionnality, using MSI domains. This is > > the case for example on systems that use the ARM GIC architecture. > > > > Introduce a new attribute ('msi_domain') indicating that implicit > > dependency, and use this property to set the NO_MSI flag when > > no MSI domain is found at probe time. > > > > Acked-by: Bjorn Helgaas > > Signed-off-by: Marc Zyngier > > --- > > drivers/pci/probe.c | 2 +- > > include/linux/pci.h | 1 + > > 2 files changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > > index 146bd85c037e..bac9f69a06a8 100644 > > --- a/drivers/pci/probe.c > > +++ b/drivers/pci/probe.c > > @@ -925,7 +925,7 @@ static int pci_register_host_bridge(struct pci_host_bridge *bridge) > > device_enable_async_suspend(bus->bridge); > > pci_set_bus_of_node(bus); > > pci_set_bus_msi_domain(bus); > > - if (bridge->no_msi) > > + if (bridge->no_msi || (bridge->msi_domain && !bus->dev.msi_domain)) > > bus->bus_flags |= PCI_BUS_FLAGS_NO_MSI; > > if (!parent) > > diff --git a/include/linux/pci.h b/include/linux/pci.h > > index 48605cca82ae..d322d00db432 100644 > > --- a/include/linux/pci.h > > +++ b/include/linux/pci.h > > @@ -551,6 +551,7 @@ struct pci_host_bridge { > > unsigned int preserve_config:1; /* Preserve FW resource setup */ > > unsigned int size_windows:1; /* Enable root bus sizing */ > > unsigned int no_msi:1; /* Bridge has no MSI support */ > > + unsigned int msi_domain:1; /* Bridge wants MSI domain */ > > Aren't these really the same thing? Either way we're saying the bridge > itself doesn't handle MSIs, it's just in one case we're effectively > encoding a platform-specific assumption that an external domain won't > be provided. I can't help wondering whether that distinction is really > necessary... There is a subtle difference: no_msi indicates that there is no way *any* MSI can be dealt with whatsoever (maybe because the RC doesn't forward the corresponding TLPs?). msi_domain says "no MSI unless...". We could implement the former with the latter, but I have the feeling that's not totally bullet proof. Happy to revisit this if you think it really matters. Thanks, M. -- Without deviation from the norm, progress is not possible.