>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 <[email protected]> --- 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"))); -- 2.43.0
