Re: [PATCH v2 0/4] isa-serial: acpi: declare shared IRQs for COM1/3 and COM2/4

[Igor Mammedov <imammedo@redhat.com>]

On Wed, 11 Mar 2026 16:24:25 +0000
Mark Cave-Ayland <mark.caveayland@nutanix.com> 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

nitpicking but pc/q35 ship rev 3.0 facp, it is worth mentioning CLI used to reproduce/test
 
> 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.
> 
> Add a new 3-byte IRQ Descriptor to the _CRS resource 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.
> 
> Tested on Windows 8.1 and Windows 11 with 4 instances of -serial on the command
> line and copying data simultaneously across serial ports COM1/3 and COM2/4.
> Note that with this series applied, if extra ISA serial ports are added to an
> existing VM then it is necessary to go to Device Manager, select "Add legacy
> hardware" from the "Action" menu, and then reboot the VM for the serial ports
> to be detected correctly without Device Manager indicating a conflict.




> 
> Signed-off-by: Mark Cave-Ayland <mark.caveayland@nutanix.com>
> 
> v2
> - Remove _PRS changes (including AML build changes that are no longer required)
>   and compatibility property as suggested by Igor
> 
> 
> Mark Cave-Ayland (4):
>   hw/acpi/aml-build.c: add aml_irq() representing the 3-byte IRQ
>     descriptor
>   tests/acpi: allow DSDT acpi table changes
>   hw/char/serial-isa.c: declare IRQ as shared in ACPI IRQ descriptor
>   tests: data: update x86 ACPI tables
> 
>  include/hw/acpi/aml-build.h                   |   2 ++
>  hw/acpi/aml-build-stub.c                      |   6 +++++
>  hw/acpi/aml-build.c                           |  25 ++++++++++++++++++
>  hw/char/serial-isa.c                          |   3 ++-
>  tests/data/acpi/x86/microvm/DSDT              | Bin 365 -> 366 bytes
>  tests/data/acpi/x86/microvm/DSDT.ioapic2      | Bin 365 -> 366 bytes
>  tests/data/acpi/x86/microvm/DSDT.pcie         | Bin 2985 -> 2986 bytes
>  tests/data/acpi/x86/microvm/DSDT.rtc          | Bin 404 -> 405 bytes
>  tests/data/acpi/x86/microvm/DSDT.usb          | Bin 414 -> 415 bytes
>  tests/data/acpi/x86/pc/DSDT                   | Bin 8598 -> 8599 bytes
>  tests/data/acpi/x86/pc/DSDT.acpierst          | Bin 8509 -> 8510 bytes
>  tests/data/acpi/x86/pc/DSDT.acpihmat          | Bin 9923 -> 9924 bytes
>  tests/data/acpi/x86/pc/DSDT.bridge            | Bin 15469 -> 15470 bytes
>  tests/data/acpi/x86/pc/DSDT.cphp              | Bin 9062 -> 9063 bytes
>  tests/data/acpi/x86/pc/DSDT.dimmpxm           | Bin 10252 -> 10253 bytes
>  tests/data/acpi/x86/pc/DSDT.hpbridge          | Bin 8549 -> 8550 bytes
>  tests/data/acpi/x86/pc/DSDT.hpbrroot          | Bin 5087 -> 5088 bytes
>  tests/data/acpi/x86/pc/DSDT.ipmikcs           | Bin 8670 -> 8671 bytes
>  tests/data/acpi/x86/pc/DSDT.memhp             | Bin 9957 -> 9958 bytes
>  tests/data/acpi/x86/pc/DSDT.nohpet            | Bin 8456 -> 8457 bytes
>  tests/data/acpi/x86/pc/DSDT.numamem           | Bin 8604 -> 8605 bytes
>  tests/data/acpi/x86/pc/DSDT.roothp            | Bin 12391 -> 12392 bytes
>  tests/data/acpi/x86/q35/DSDT                  | Bin 8427 -> 8428 bytes
>  tests/data/acpi/x86/q35/DSDT.acpierst         | Bin 8444 -> 8445 bytes
>  tests/data/acpi/x86/q35/DSDT.acpihmat         | Bin 9752 -> 9753 bytes
>  .../data/acpi/x86/q35/DSDT.acpihmat-generic-x | Bin 12637 -> 12638 bytes
>  .../acpi/x86/q35/DSDT.acpihmat-noinitiator    | Bin 8706 -> 8707 bytes
>  tests/data/acpi/x86/q35/DSDT.applesmc         | Bin 8473 -> 8474 bytes
>  tests/data/acpi/x86/q35/DSDT.bridge           | Bin 12040 -> 12041 bytes
>  tests/data/acpi/x86/q35/DSDT.core-count       | Bin 12985 -> 12986 bytes
>  tests/data/acpi/x86/q35/DSDT.core-count2      | Bin 33842 -> 33843 bytes
>  tests/data/acpi/x86/q35/DSDT.cphp             | Bin 8891 -> 8892 bytes
>  tests/data/acpi/x86/q35/DSDT.cxl              | Bin 13218 -> 13219 bytes
>  tests/data/acpi/x86/q35/DSDT.dimmpxm          | Bin 10081 -> 10082 bytes
>  tests/data/acpi/x86/q35/DSDT.ipmibt           | Bin 8502 -> 8503 bytes
>  tests/data/acpi/x86/q35/DSDT.ipmismbus        | Bin 8515 -> 8516 bytes
>  tests/data/acpi/x86/q35/DSDT.ivrs             | Bin 8444 -> 8445 bytes
>  tests/data/acpi/x86/q35/DSDT.memhp            | Bin 9786 -> 9787 bytes
>  tests/data/acpi/x86/q35/DSDT.mmio64           | Bin 9557 -> 9558 bytes
>  tests/data/acpi/x86/q35/DSDT.multi-bridge     | Bin 13280 -> 13281 bytes
>  tests/data/acpi/x86/q35/DSDT.noacpihp         | Bin 8289 -> 8290 bytes
>  tests/data/acpi/x86/q35/DSDT.nohpet           | Bin 8285 -> 8286 bytes
>  tests/data/acpi/x86/q35/DSDT.numamem          | Bin 8433 -> 8434 bytes
>  tests/data/acpi/x86/q35/DSDT.pvpanic-isa      | Bin 8528 -> 8529 bytes
>  tests/data/acpi/x86/q35/DSDT.thread-count     | Bin 12985 -> 12986 bytes
>  tests/data/acpi/x86/q35/DSDT.thread-count2    | Bin 33842 -> 33843 bytes
>  tests/data/acpi/x86/q35/DSDT.tis.tpm12        | Bin 9033 -> 9034 bytes
>  tests/data/acpi/x86/q35/DSDT.tis.tpm2         | Bin 9059 -> 9060 bytes
>  tests/data/acpi/x86/q35/DSDT.type4-count      | Bin 18661 -> 18662 bytes
>  tests/data/acpi/x86/q35/DSDT.viot             | Bin 14684 -> 14685 bytes
>  tests/data/acpi/x86/q35/DSDT.xapic            | Bin 35790 -> 35791 bytes
>  51 files changed, 35 insertions(+), 1 deletion(-)
>