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Thu, 30 Apr 2026 01:45:37 -0700 (PDT) X-Received: by 2002:a05:620a:4804:b0:8f4:3bb0:ca7 with SMTP id af79cd13be357-8fa88942d82mr307555485a.37.1777538736651; Thu, 30 Apr 2026 01:45:36 -0700 (PDT) Received: from imammedo ([213.175.37.14]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8f93fc68102sm372044485a.34.2026.04.30.01.45.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Apr 2026 01:45:36 -0700 (PDT) Date: Thu, 30 Apr 2026 10:45:34 +0200 From: Igor Mammedov To: Mark Cave-Ayland Cc: mst@redhat.com, anisinha@redhat.com, pbonzini@redhat.com, marcandre.lureau@redhat.com, marcel.apfelbaum@gmail.com, qemu-devel@nongnu.org Subject: Re: [PATCH v2 3/4] hw/char/serial-isa.c: declare IRQ as shared in ACPI IRQ descriptor Message-ID: <20260430104534.0fa36276@imammedo> In-Reply-To: <20260311162605.2976339-4-mark.caveayland@nutanix.com> References: <20260311162605.2976339-1-mark.caveayland@nutanix.com> <20260311162605.2976339-4-mark.caveayland@nutanix.com> X-Mailer: Claws Mail 4.4.0 (GTK 3.24.52; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=imammedo@redhat.com; helo=us-smtp-delivery-124.mimecast.com 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, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-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: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Wed, 11 Mar 2026 16:24:28 +0000 Mark Cave-Ayland wrote: > From Windows 8.1 onwards ISA serial IRQs cannot be shared when ACPI Revision > 5.0 is used in the FACP table. The reason for this is that if a 2-byte IRQ > Descriptor is used then the interrupt is considered to be high true, edge > sensitive, non-shareable. Since legacy serial ports COM1/3 and COM2/4 share > an IRQ then if more than 2 serial ports are added, Windows indicates a > conflict in Device Manager and these combinations cannot be used together. > > Change the 2-byte IRQ Descriptor in the _CRS resource to a 3-byte IRQ > Descriptor indicating that the ISA serial IRQ is low true, edge sensitive and > shareable. This enables all 4 legacy serial ports to be used in Windows without > conflict. > > Note that it was agreed during the list discussion that this change does not > require a compatibility property since it is not part of the default machine > configuration and was already broken. > > Signed-off-by: Mark Cave-Ayland > --- > hw/char/serial-isa.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/hw/char/serial-isa.c b/hw/char/serial-isa.c > index a4be0492c5..686336f34f 100644 > --- a/hw/char/serial-isa.c > +++ b/hw/char/serial-isa.c > @@ -92,7 +92,8 @@ static void serial_isa_build_aml(AcpiDevAmlIf *adev, Aml *scope) > > crs = aml_resource_template(); > aml_append(crs, aml_io(AML_DECODE16, isa->iobase, isa->iobase, 0x00, 0x08)); > - aml_append(crs, aml_irq_no_flags(isa->isairq)); > + aml_append(crs, aml_irq(isa->isairq, AML_EDGE, AML_ACTIVE_LOW, > + AML_SHARED)); this combination looks wrong, ACPI 5.0, 6.4.2.1 IRQ Descriptor Note: This descriptor is meant for describing interrupts that are connected to PIC-compatible interrupt controllers, which can only be programmed for Active-High-Edge-Triggered or Active- Low-Level-Triggered interrupts. Any other combination is invalid. The Extended Interrupt Descriptor can be used to describe other combinations. > > dev = aml_device("COM%d", isa->index + 1); > aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0501")));