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Thu, 14 May 2026 06:37:16 -0700 (PDT) X-Received: by 2002:a05:6000:22c7:b0:43b:3e40:2223 with SMTP id ffacd0b85a97d-45c58884933mr12058947f8f.19.1778765836223; Thu, 14 May 2026 06:37:16 -0700 (PDT) Received: from imammedo ([213.175.46.86]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45d9adc2209sm6139706f8f.0.2026.05.14.06.37.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 14 May 2026 06:37:15 -0700 (PDT) Date: Thu, 14 May 2026 15:37:14 +0200 From: Igor Mammedov To: Mark Cave-Ayland Cc: mst@redhat.com, anisinha@redhat.com, pbonzini@redhat.com, marcandre.lureau@redhat.com, qemu-devel@nongnu.org Subject: Re: [PATCH v3 3/4] hw/char/serial-isa.c: declare IRQ as shared in ACPI IRQ descriptor Message-ID: <20260514153714.1cd2721b@imammedo> In-Reply-To: <20260508101901.930781-4-mark.caveayland@nutanix.com> References: <20260508101901.930781-1-mark.caveayland@nutanix.com> <20260508101901.930781-4-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=170.10.133.124; envelope-from=imammedo@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, 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_H5=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 Fri, 8 May 2026 11:17:42 +0100 Mark Cave-Ayland wrote: > From Windows 8.1 onwards ISA serial IRQs cannot be shared when ACPI Revision > 3.0 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 high 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 Reviewed-by: Igor Mammedov > --- > 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..59df726871 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_HIGH, > + AML_SHARED)); > > dev = aml_device("COM%d", isa->index + 1); > aml_append(dev, aml_name_decl("_HID", aml_eisaid("PNP0501")));