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[83.42.66.234]) by smtp.gmail.com with ESMTPSA id m14sm6566491wro.43.2020.11.07.06.18.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 07 Nov 2020 06:18:25 -0800 (PST) Subject: Re: [PULL v4 44/48] piix4: don't reserve hw resources when hotplug is off globally To: Ani Sinha References: <20200929071948.281157-1-mst@redhat.com> <20200929071948.281157-45-mst@redhat.com> <5b79133f-374e-8a8f-6aeb-bd5313dc8eb1@redhat.com> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: <56a067f8-945f-cab4-d80e-6706ae446705@redhat.com> Date: Sat, 7 Nov 2020 15:18:24 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=philmd@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/11/07 03:12:58 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Eduardo Habkost , "Michael S. Tsirkin" , QEMU Developers , Aleksandar Markovic , Igor Mammedov , Paolo Bonzini , Aurelien Jarno , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 11/7/20 1:22 PM, Ani Sinha wrote: > On Sat, Nov 7, 2020 at 3:40 PM Philippe Mathieu-Daudé wrote: >> >> Hi, >> >> On 9/29/20 9:22 AM, Michael S. Tsirkin wrote: >>> From: Ani Sinha >>> >>> When acpi hotplug is turned off for both root pci bus as well as for pci >>> bridges, we should not generate the related ACPI code for DSDT table or >>> initialize related hw ports or reserve hw resources. This change makes >>> sure all those operations are turned off in the case ACPI pci hotplug is >>> off globally. >>> >>> In this change, we also make sure ACPI code for the PCNT method are only >>> added when bsel is enabled for the corresponding pci bus or bridge hotplug >>> is turned on. >> >> I'm trying to understand the following build failure using gcc 9.3.0 >> on Ubuntu: >> >> [2567/3684] Compiling C object >> libqemu-x86_64-softmmu.fa.p/hw_i386_acpi-build.c.o >> FAILED: libqemu-x86_64-softmmu.fa.p/hw_i386_acpi-build.c.o >> ../hw/i386/acpi-build.c: In function 'build_append_pci_bus_devices': >> ../hw/i386/acpi-build.c:496:9: error: 'method' may be used uninitialized >> in this function [-Werror=maybe-uninitialized] >> 496 | aml_append(parent_scope, method); >> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >> cc1: all warnings being treated as errors >> ... >>> static void acpi_get_misc_info(AcpiMiscInfo *info) >>> @@ -456,10 +460,12 @@ static void build_append_pci_bus_devices(Aml *parent_scope, PCIBus *bus, >>> } >>> >>> /* Append PCNT method to notify about events on local and child buses. >>> - * Add unconditionally for root since DSDT expects it. >>> + * Add this method for root bus only when hotplug is enabled since DSDT >>> + * expects it. >>> */ >>> - method = aml_method("PCNT", 0, AML_NOTSERIALIZED); >>> - >>> + if (bsel || pcihp_bridge_en) { >>> + method = aml_method("PCNT", 0, AML_NOTSERIALIZED); >>> + } >> >> build_append_pci_bus_devices() is not easy to follow and could certainly >> benefit from a refactor. > > Hmm, ok will do that in my spare time. > >> >> So here, before 'method' was always reinitialized. Now not always, >> so it can be any value set in the big for() loop before... > > In line 467 above, method is initialized when bsel is available or > pcihp is enabled. In line 496, it is appended to the parent scope only > under those conditions as well. Basically, in hunks > > + if (bsel || pcihp_bridge_en) { > + method = aml_method("PCNT", 0, AML_NOTSERIALIZED); > + } > > and > + > + if (bsel || pcihp_bridge_en) { > + aml_append(parent_scope, method); > + } > > the conditions are exactly the same. The problem is in the (!bsel && !pcihp_bridge_en) case, what 'method' is used there?