On Thu, 11 Dec 2025 at 10:21, Li Chen <[email protected]> wrote: > > From: Li Chen <[email protected]> > > virt machines always instantiate a PL011/16550 UART at slot 0 and describe > it in ACPI (DSDT and optional SPCR table). When the command line disables > the serial backend (e.g. "-serial none"), the guest still sees the UART as > a preferred console even though it is not usable. > > Teach the virt ACPI code to omit the UART device and SPCR when there is no > serial backend attached. This matches the hardware that the guest can > actually use and avoids confusing firmware or OS code that relies on SPCR. > > The bios-tables-test qtests rely on an ACPI UART node and SPCR entry for > UEFI-based virt machines. To keep those tests working we create a UART > with a "null" chardev backend instead. This preserves the ACPI tables > while discarding the firmware's serial output so it does not corrupt the > TAP stdout stream. > > Suggested-by: Philippe Mathieu-Daudé <[email protected]> > Signed-off-by: Li Chen <[email protected]> > Reviewed-by: Sunil V L <[email protected]>
Sorry, I must have missed this patch previously. I'm not sure that this is a good idea, because it means: * the dtb version of virt and the ACPI handling diverge * we tangle up "what chardev do you want to connect serial output to" and "what UARTs does the guest see" If the user explicitly sends the first serial port output to nowhere with "-serial none -serial stdio" they presumably had a reason for that and won't be happy to find that we've adjusted the ACPI tables to redirect that output to the second serial port they were planning to use for something else. thanks -- PMM
