Re: [PATCH v2] mc146818rtc: add a way to generate RTC interrupts via QMP

[Markus Armbruster <armbru@redhat.com>]

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

> On 29/4/24 11:41, Daniil Tatianin wrote:
>> This can be used to force-synchronize the time in guest after a long
>> stop-cont pause, which can be useful for serverless-type workload.
>> Also add a comment to highlight the fact that this (and one other QMP
>> command) only works for the MC146818 RTC controller.
>> Signed-off-by: Daniil Tatianin <d-tatianin@yandex-team.ru>
>> ---
>> Changes since v0:
>> - Rename to rtc-inject-irq to match other similar API
>> - Add a comment to highlight that this only works for the I386 RTC
>> Changes since v1:
>> - Added a description below the QMP command to explain how it can be
>>    used and what it does.

[...]

>> diff --git a/qapi/misc-target.json b/qapi/misc-target.json
>> index 4e0a6492a9..0f2479f8f4 100644
>> --- a/qapi/misc-target.json
>> +++ b/qapi/misc-target.json
>> @@ -19,6 +19,24 @@
>>   { 'command': 'rtc-reset-reinjection',
>>     'if': 'TARGET_I386' }
>> +##
>> +# @rtc-inject-irq:
>> +#
>> +# Inject an RTC interrupt. This command forces the guest to synchornize

synchronize

>> +# the time with RTC. This is useful after a long stop-cont pause, which
>> +# is common for serverless-type workload.

docs/devel/qapi-code-gen.rst:

    For legibility, wrap text paragraphs so every line is at most 70
    characters long.

    Separate sentences with two spaces.

>> +#
>> +# Since: 9.1
>> +#
>> +# Example:
>> +#
>> +#     -> { "execute": "rtc-inject-irq" }
>> +#     <- { "return": {} }
>> +#
>> +##
>> +{ 'command': 'rtc-inject-irq',
>> +  'if': 'TARGET_I386' }
>
> Why is that restricted to x86? Ah, this is specific to the MC146818
> RTC... Other machines use hw accelerators and the MC146818, aren't
> we interested in synchronizing them the same way?
>
> Personally I'd name this command 'mc146818rtc-raise-irq-broadcast',
> KISS.

I might be wrong, but the *interface* looks general to me, only nobody
bothered to implement for the other RTCs.