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Re: [PATCH v4 2/3] hw/acpi: add indication for i8042 in IA-PC boot flags


From: Liav Albani
Subject: Re: [PATCH v4 2/3] hw/acpi: add indication for i8042 in IA-PC boot flags of the FADT table
Date: Wed, 2 Mar 2022 17:43:47 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1


On 3/2/22 14:42, Michael S. Tsirkin wrote:
On Wed, Mar 02, 2022 at 10:44:03AM +0530, Ani Sinha wrote:
On Wed, Mar 2, 2022 at 12:50 AM Liav Albani <liavalb@gmail.com> wrote:

On 3/1/22 11:52, Ani Sinha wrote:
On Tue, 1 Mar 2022, Igor Mammedov wrote:

On Mon, 28 Feb 2022 22:17:32 +0200
Liav Albani <liavalb@gmail.com> wrote:

This can allow the guest OS to determine more easily if i8042 controller
is present in the system or not, so it doesn't need to do probing of the
controller, but just initialize it immediately, before enumerating the
ACPI AML namespace.

This change only applies to the x86/q35 machine type, as it uses FACP
ACPI table with revision higher than 1, which should implement at least
ACPI 2.0 features within the table, hence it can also set the IA-PC boot
flags register according to the ACPI 2.0 specification.

Signed-off-by: Liav Albani <liavalb@gmail.com>
---
   hw/acpi/aml-build.c         | 11 ++++++++++-
   hw/i386/acpi-build.c        |  9 +++++++++
   hw/i386/acpi-microvm.c      |  9 +++++++++
commit message says it's q35 specific, so wy it touched microvm anc piix4?
Igor is correct. Although I see that currently there are no 8042 devices
for microvms, maybe we should be conservative and add the code to detect
the device anyway. In that case, the change could affect microvms too when
such devices get added in the future.


echo -e "info qtree\r\nquit\r\n" | ./qemu-system-x86_64 -machine microvm
-monitor stdio 2>/dev/null | grep 8042

<empty>
What about this?

echo -e "info qtree\r\nquit\r\n" | qemu-system-x86_64 -machine microvm
-device i8042 -monitor stdio 2>/dev/null | grep 8042

Or this?

echo -e "info mtree\r\nquit\r\n" | qemu-system-x86_64 -machine microvm
-device i8042 -monitor stdio 2>/dev/null | grep 8042
On both occasions you are explicitly adding the device.
Yes of course. It seems a bit cleaner to have -device i8042 -monitor
stdio give us the correct ACPI table even if there's no pressing need
for this ATM, simply because it's not much more code, and because if we
don't we risk guests trying to work around incorrect ACPI tables.
Let us however do this in a patch by its own with proper
documentation and motivation.

So if I understand how to do this now - I should drop the code for the MicroVM ACPI for now, letting only to change the Q35 FACP table, right? So if that's the case I should send it in a separate patch?

If that's the case, as suggested by you and Ani, I'll not add a separate function to reduce code duplication as there's no such thing in such case...




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