Re: [PATCH v4] hw/rtc/mc146818rtc: Make this rtc device target independent

[Thomas Huth <thuth@redhat.com>]

On 02/01/2023 14.36, Thomas Huth wrote:
> On 31/12/2022 00.45, Bernhard Beschow wrote:
>>
>> Am 29. Dezember 2022 10:58:48 UTC schrieb Thomas Huth <thuth@redhat.com>:
[...]
>>> static uint32_t rtc_periodic_clock_ticks(RTCState *s)
>>> {
>>> @@ -922,14 +911,15 @@ static void rtc_realizefn(DeviceState *dev, Error 
>>> **errp)
>>>      rtc_set_date_from_host(isadev);
>>>
>>>      switch (s->lost_tick_policy) {
>>> -#ifdef TARGET_I386
>>> -    case LOST_TICK_POLICY_SLEW:
>>> -        s->coalesced_timer =
>>> -            timer_new_ns(rtc_clock, rtc_coalesced_timer, s);
>>> -        break;
>>> -#endif
>>>      case LOST_TICK_POLICY_DISCARD:
>>>          break;
>>> +    case LOST_TICK_POLICY_SLEW:
>>> +        /* Slew tick policy is only available on x86 */
>>> +        if (arch_type == QEMU_ARCH_I386) {
>>
>> This reflects the intention much better than before, which is nice.
>>
>> How does `arch_type` play together with qemu-system-all? IIUC it should be 
>> possible to load all arch backends simultaneously while `arch_type` is an 
>> external symbol defined by each arch backend differently. So this seems to 
>> conflict.
> 
> I assume that there still will be a main arch_type for the current selected 
> machine? ... not sure how this will exactly work, though ...
> 
>> Can we just add a property such as "slew-tick-policy-available" instead? 
>> It should default to false and all x86 machines would need to opt in 
>> explicitly.
> 
> Sounds like a good idea, it's certainly better than checking arch_type here 
> ... I'll give it a try, thanks!

I've now had a look at this, and it's also getting ugly: Since the property 
has to be set before realize() is done, the setting of the property has to 
be added to the mc146818_rtc_init() function. Thus this function would need 
a new parameter - and it then needs to be changed all over the place, i.e. 
also for all the non-x86 machines, defeating the idea of a default value...

Maybe it makes more sense to check for a TYPE_X86_MACHINE machine type instead?

  Thomas