Re: [PATCH v1] mc146818rtc: add a way to generate RTC interrupts via QMP

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 29/4/24 11:34, Daniil Tatianin wrote:
> On 4/29/24 11:51 AM, Markus Armbruster wrote:
> 
>> Daniil Tatianin <d-tatianin@yandex-team.ru> writes:
>>
>>> 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
>>>
>>> ---
>>>   hw/rtc/mc146818rtc.c         | 20 ++++++++++++++++++++
>>>   include/hw/rtc/mc146818rtc.h |  1 +
>>>   qapi/misc-target.json        | 16 ++++++++++++++++
>>>   3 files changed, 37 insertions(+)
>>>
>>> diff --git a/hw/rtc/mc146818rtc.c b/hw/rtc/mc146818rtc.c
>>> index f4c1869232..8501b55cbd 100644
>>> --- a/hw/rtc/mc146818rtc.c
>>> +++ b/hw/rtc/mc146818rtc.c
>>> @@ -107,6 +107,11 @@ static void 
>>> rtc_coalesced_timer_update(MC146818RtcState *s)
>>>   static QLIST_HEAD(, MC146818RtcState) rtc_devices =
>>>       QLIST_HEAD_INITIALIZER(rtc_devices);
>>> +/*
>>> + * NOTE:
>>> + * The two QMP functions below are _only_ implemented for the MC146818.
>>> + * All other RTC devices ignore this.
>>> + */
>>>   void qmp_rtc_reset_reinjection(Error **errp)
>>>   {
>>>       MC146818RtcState *s;
>>> @@ -116,6 +121,21 @@ void qmp_rtc_reset_reinjection(Error **errp)
>>>       }
>>>   }
>>> +void qmp_rtc_inject_irq(Error **errp)
>>> +{
>>> +    MC146818RtcState *s;
>>> +
>>> +    /*
>>> +     * See:
>>> +     * 
>>> https://www.kernel.org/doc/Documentation/virtual/kvm/timekeeping.txt
>>> +     */
>>> +    QLIST_FOREACH(s, &rtc_devices, link) {
>>> +        s->cmos_data[RTC_REG_B] |= REG_B_UIE;
>>> +        s->cmos_data[RTC_REG_C] |= REG_C_IRQF | REG_C_UF;
>>> +        qemu_irq_raise(s->irq);
>>> +    }
>>> +}
>>> +
>>>   static bool rtc_policy_slew_deliver_irq(MC146818RtcState *s)
>>>   {
>>>       kvm_reset_irq_delivered();
>>> diff --git a/include/hw/rtc/mc146818rtc.h b/include/hw/rtc/mc146818rtc.h
>>> index 97cec0b3e8..6cd9761d80 100644
>>> --- a/include/hw/rtc/mc146818rtc.h
>>> +++ b/include/hw/rtc/mc146818rtc.h
>>> @@ -56,5 +56,6 @@ MC146818RtcState *mc146818_rtc_init(ISABus *bus, 
>>> int base_year,
>>>   void mc146818rtc_set_cmos_data(MC146818RtcState *s, int addr, int 
>>> val);
>>>   int mc146818rtc_get_cmos_data(MC146818RtcState *s, int addr);
>>>   void qmp_rtc_reset_reinjection(Error **errp);
>>> +void qmp_rtc_inject_irq(Error **errp);
>>>   #endif /* HW_RTC_MC146818RTC_H */
>>> diff --git a/qapi/misc-target.json b/qapi/misc-target.json
>>> index 4e0a6492a9..d84a5d07a2 100644
>>> --- a/qapi/misc-target.json
>>> +++ b/qapi/misc-target.json
>>> @@ -19,6 +19,22 @@
>>>   { 'command': 'rtc-reset-reinjection',
>>>     'if': 'TARGET_I386' }
>>> +##
>>> +# @rtc-inject-irq:
>>> +#
>>> +# Inject an RTC interrupt.
>> Your cover letter explains what this could be good for.  Would it make
>> sense to explain it here, too?
> 
> Sure, sounds useful. I'll add a description in the next version.

Please also see my comments on the previous patch:
https://lore.kernel.org/qemu-devel/11c78645-e87b-4a43-8191-a73540c364a9@linaro.org/