Re: [Qemu-devel] [PATCH v2 4/7] s390x/tcg: SET CLOCK COMPARATOR can clear CKC interrupts

[David Hildenbrand <david@redhat.com>]

On 21.06.2018 15:58, Cornelia Huck wrote:
> On Thu, 21 Jun 2018 14:09:28 +0200
> Thomas Huth <thuth@redhat.com> wrote:
> 
>> On 20.06.2018 12:08, David Hildenbrand wrote:
>>> Let's stop the timer and delete any pending CKC IRQ before doing
>>> anything else.
>>>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>> ---
>>>  target/s390x/misc_helper.c | 6 ++++++
>>>  1 file changed, 6 insertions(+)
>>>
>>> diff --git a/target/s390x/misc_helper.c b/target/s390x/misc_helper.c
>>> index 6ccbe1fe9a..d5f9f5e1d3 100644
>>> --- a/target/s390x/misc_helper.c
>>> +++ b/target/s390x/misc_helper.c
>>> @@ -158,6 +158,12 @@ void HELPER(sckc)(CPUS390XState *env, uint64_t time)
>>>      Error *err = NULL;
>>>      S390TOD tod_base;
>>>  
>>> +    /* stop the timer and remove pending CKC IRQs */
>>> +    timer_del(env->tod_timer);
>>> +    qemu_mutex_lock_iothread();
>>> +    env->pending_int &= ~INTERRUPT_EXT_CLOCK_COMPARATOR;
>>> +    qemu_mutex_unlock_iothread();  
>>
>> Reviewed-by: Thomas Huth <thuth@redhat.com>
>>
>>>      if (time == -1ULL) {  
>>
>> I wonder whether that check is still adequate? Is there really a way to
>> disable the clock comparator like this? At least I haven't seen it in
>> the PoP.
> 
> Me neither. It seems to have been in the code since the beginning...

I agree that this is somewhat buried deep down in the PoP and not
obvious when only looking at SET CLOCK COMPARATOR  documentation.

I'll add a comment like

"we can never exceed -1 and therefore never trigger an IRQ"

-- 

Thanks,

David / dhildenb