On Thu, 26 Oct 2023 at 16:46, Julien Grall <jul...@xen.org> wrote: > > Hi, > > On 26/10/2023 15:21, Peter Maydell wrote: > > On Tue, 10 Oct 2023 at 16:33, Laszlo Ersek <ler...@redhat.com> wrote: > >> On 10/10/23 09:43, Ard Biesheuvel wrote: > >>> Thanks for looking into this - a cleanup was overdue here. > >>> > >>> I will take a look in more detail later, but one thing that occurred > >>> to me when reading this overview is that having a separate DEBUG > >>> serial port would permit us to > >>> > >>> a) remove it from the DT > >> > >> ... as in, hide it from Linux, I assume? > >> > >>> b) add a runtime mapping for it > >>> c) keep using it after ExitBootServices > >>> > >>> This could be useful for debugging issues with the variable store etc. > >>> > >>> Not saying this is something to address in this series, but I'd like > >>> to hear your take on this. > >>> > >> > >> Sounds like a useful feature. > >> > >> I see four challenges: > >> > >> > >> (1) We'd have to coordinate it with Peter. If we hide any one of the > >> serial ports from Linux, that may not be what QEMU intends for Linux to > >> happen. Linux currently ties getties to all serial ports -- via the > >> serial* aliases, IIUC. Thus, some "positive identification" in the DT > >> could be necessary (i.e., that edk2 was welcome to hide that port from > >> Linux). > > > > The potential awkwardness here is that what the guest thinks about > > the serial ports depends on the ACPI table fragments which QEMU > > provides. EDK2 would need to edit the table fragment to remove any > > mention of the second UART if it wanted to hide it from the kernel. > > I don't know how hard that would be in EDK2. > > I am not sure if it would help EDK2 in this case. But we had a similar > problem when adding support for ACPI in Xen. It was not trivial to > remove the UART from the ACPI tables provided by the host. So we ended > up to introduce the STAO table [1]. This is used to describe which > device will be hidden to the OS. >
I'd much rather have an implementation of the _STA method on those devices where the underlying AML queries the fwcfg MMIO device -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#110108): https://edk2.groups.io/g/devel/message/110108 Mute This Topic: https://groups.io/mt/101834880/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
