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

[Bernhard Beschow]

Am 2. Januar 2023 16:09:08 UTC schrieb 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?

Maybe you could base your patch on 
https://lists.gnu.org/archive/html/qemu-devel/2022-12/msg03795.html ? This 
patch looks like it should get you covered and is part of my PIIX consolidation 
series [1] which seems to be ready to be queued into Phil's mips-next tree. My 
series is currently just blocked by a MIPS-related  regression.

Best regards,
Bernhard

[1] https://lists.gnu.org/archive/html/qemu-devel/2022-12/msg03788.html

>
> Thomas
>