Re: [Qemu-devel] [PATCH v3 2/7] hpet: Save/restore cached RTC IRQ level

[Jan Kiszka <jan.kiszka@web.de>]

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On 2012-01-31 23:38, Anthony Liguori wrote:
> On 01/31/2012 04:05 PM, Jan Kiszka wrote:
>> On 2012-01-31 22:02, Anthony Liguori wrote:
>>> On 01/31/2012 11:41 AM, Jan Kiszka wrote:
>>>> In legacy mode, the HPET suppresses the RTC interrupt delivery via IRQ
>>>> 8 but keeps track of the RTC output level and applies it when legacy
>>>> mode is turned off again. This value has to be preserved across save/
>>>> restore as it cannot be reconstructed otherwise.
>>>>
>>>> Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
>>>> ---
>>>>    hw/hpet.c |   26 ++++++++++++++++++++++++++
>>>>    1 files changed, 26 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/hw/hpet.c b/hw/hpet.c
>>>> index aba9ea9..39b291f 100644
>>>> --- a/hw/hpet.c
>>>> +++ b/hw/hpet.c
>>>> @@ -240,6 +240,24 @@ static int hpet_post_load(void *opaque, int
>>>> version_id)
>>>>        return 0;
>>>>    }
>>>>
>>>> +static bool hpet_rtc_irq_level_needed(void *opaque)
>>>> +{
>>>> +    HPETState *s = opaque;
>>>> +
>>>> +    return s->rtc_irq_level != 0;
>>>> +}
>>>> +
>>>> +static const VMStateDescription vmstate_hpet_rtc_irq_level = {
>>>> +    .name = "hpet/rtc_irq_level",
>>>> +    .version_id = 1,
>>>> +    .minimum_version_id = 1,
>>>> +    .minimum_version_id_old = 1,
>>>> +    .fields      = (VMStateField[]) {
>>>> +        VMSTATE_UINT8(rtc_irq_level, HPETState),
>>>> +        VMSTATE_END_OF_LIST()
>>>> +    }
>>>> +};
>>>> +
>>>
>>> This won't work.  We don't clear rtc_irq_level on reset so rtc_irq_level
>>> may be high or low after reset.  As such, we can't use a subsection
>>> here.  We need to bump the savevm state.
>>
>> rtc_irq_level is updated during reset by the connected RTC device. It
>> clears its IRQ line.
> 
> Ah, that's subtle and warrants a comment :-)
> 
> Probably worth adding an s->rtc_irq_level = 0 in reset just to be extra
> safe.

Agreed. Will do.

Thanks,
Jan


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