Re: riscv64 virt board crash upon startup

[Laszlo Ersek <lersek@redhat.com>]

On 9/11/23 15:12, Laszlo Ersek wrote:
> On 9/11/23 10:53, Gerd Hoffmann wrote:
>> On Mon, Sep 11, 2023 at 12:12:43PM +0400, Marc-André Lureau wrote:
>>>> Gerd, here's the question for you: why are "device" and "head" QOM properties in the first place? What are they needed for?
>>>>
>>>
>>> You get QOM tree introspection (ex: (qemu) qom-get
>>> /backend/console[0]/device type). Other than that, I don't think it
>>> brings anything else.
>>
>> You can configure vnc server(s) to show a specific device + head, which
>> allows to run multihead configurations by using multiple vnc servers (one
>> for each head).
>>
>> You can link input devices to device + head, so input events can go to
>> different devices depending on where they are coming from.  Which is
>> most useful for tablet devices in a vnc multihead setup, each head has
>> its own tablet device then.  Requires manual guest-side configuration
>> to establish the same tablet <-> head relationship (tested that years
>> ago with X11, not sure if and how this can be done with wayland).
> 
> OK, so I'm going to drop patch#3.

Hmmm, wait, I originally asked about the "QOM trickery" for a different
reason.

There are two things:

- using (exposing) QOM properties for introspection,

- using those propreties for internal access.

Patch#3 would eliminate property use *internally*, it would not
interfere with the use case explained by Gerd.

I originally asked about QOM because I wanted to know where to *stop
removing* QOM stuff. Like, once I replaced the QOM accessors with normal
C struct / field accesses in qemu_console_is_multihead(), why would I
stop there, and not just remove the "head" and and "device" properties
altogether?

With Gerd's explanation, I understand we need to keep those properties
-- but that doesn't seem to imply we *must* use the properties even in
internal functions such as qemu_console_is_multihead(). There, we can
just go for direct field access; is that right? (IOW I'd still keep
patch#3, if I can!)

Thanks!
Laszlo