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From: Thomas Huth <thuth@redhat.com>
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Date: Thu, 21 Jun 2018 16:01:10 +0200
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Subject: Re: [Qemu-devel] [qemu-s390x] [PATCH v2 4/7] s390x/tcg: SET CLOCK
 COMPARATOR can clear CKC interrupts
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To: David Hildenbrand <david@redhat.com>, qemu-s390x@nongnu.org
Cc: Alexander Graf <agraf@suse.de>, Cornelia Huck <cohuck@redhat.com>, qemu-devel@nongnu.org, Christian Borntraeger <borntraeger@de.ibm.com>, Richard Henderson <rth@twiddle.net>

On 21.06.2018 15:54, David Hildenbrand wrote:
> On 21.06.2018 14:09, Thomas Huth wrote:
>> On 20.06.2018 12:08, David Hildenbrand wrote:
[...]
>>>      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.
> 
> e.g. 4-61 (Control)
> 
> 4. When the clock-comparator sign control is zero,
> (a) the program can set the clock comparator to
> all zeros to ensure that an interruption condition
> is immediately present, and (b) the program can
> set the clock comparator to a value of all binary
> ones to ensure that a clock-comparator interrup-
> tion is never recognized. [...]
> 
> Rational from 4-59 (Control):
> 
> The clock comparator provides a means of causing
> an interruption when the TOD-clock value exceeds a
> value specified by the program.
> 
> We can never exceed all binary 1s. So it is really exceeding, not "hitting"

Thanks! ... maybe you could add a comment to the code with a pointer to
that section in the PoP while you're at it? (just if you agree that it
is useful)

 Thomas