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Date: Sat, 22 Feb 2014 15:39:59 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] Don't enable a HPET timer if HPET is
	disabled
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To: Alex Bligh <alex@alex.org.uk>
Cc: QEMU Developers <qemu-devel@nongnu.org>, Matt Lupfer <mlupfer@ddn.com>

Il 22/02/2014 13:25, Alex Bligh ha scritto:
> Paolo,
>
> On 22 Feb 2014, at 10:55, Paolo Bonzini wrote:
>
>> Il 22/02/2014 10:03, Alex Bligh ha scritto:
>>> I am unfamiliar with the HPET code but symmetry suggests perhaps the 'else'
>>> condition should be changed too:
>>>
>>>            } else if (deactivating_bit(old_val, new_val, HPET_TN_ENABLE) ||
>>>                       !hpet_enabled(s)) {
>>>                      hpet_del_timer(timer);
>>>            }
>>>
>>> --
>>
>> I thought the same, but there is no need for that.  When the enabled bit goes
>> from set to clear, all timers are disabled:
>>
>>            } else if (deactivating_bit(old_val, new_val, HPET_CFG_ENABLE)) {
>>                /* Halt main counter and disable interrupt generation. */
>>                s->hpet_counter = hpet_get_ticks(s);
>>                for (i = 0; i < s->num_timers; i++) {
>>                    hpet_del_timer(&s->timer[i]);
>>                }
>>            }
>>
>> So hpet_del_timer would be a nop if !hpet_enabled(s).
>
> Thanks. I didn't know whether HPET_CFG_ENABLE and HPET_TN_ENABLE were equivalent.

No, they are not, but HPET_CFG_ENABLE is equivalent to hpet_enabled.

Paolo