Re: [PATCH] mc146818rtc: add a way to generate RTC interrupts via QMP

[Markus Armbruster]

Philippe Mathieu-Daudé <philmd@linaro.org> writes:

> (+Peter who has more experience on such design).
>
> On 29/4/24 13:32, Markus Armbruster wrote:
>> Philippe Mathieu-Daudé <philmd@linaro.org> writes:

[...]

>>> IMO to avoid any future ambiguity (in heterogeneous machines), this
>>> command must take a QOM device path (or a list of) and only notify
>>> those.
>> 
>> Let's compare:
>> 
>> • With QOM path:
>> 
>>    · You need to know the machine's RTC device(s).
>> 
>>      Unfortunately, this is bothersome, as the QOM path is not stable.
>
> But we'll need more of that with dynamic machines...

I view /machine/unattached a technical debt (see "hate" right below).

It saved us the trouble of coming up with sensible names for onboard
devices.

And now the interest is about to be due.

>>      For Q35, it's generally "/machine/unattached/device[N]/rtc", but N
>>      varies with configuration (TCG N=2, KVM N=3 for me), and it might
>>      vary with machine type version.  That's because the machine code
>>      creates ICH9-LPC without a proper name.  We do that a lot.  I hate
>>      it.
>> 
>>      Likewise for i440FX with PIIX3 instead of ICH9-LPC.
>> 
>>      For isapc, it's /machine/unattached/device[3].  I suspect the 3
>>      isn't reliable there, either.
>> 
>>      microvm doesn't seem to have an RTC by default.

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