Re: [PATCH] reset edge sense circuit of i8259 on init

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-01-24 14:46, Gleb Natapov wrote:
> On Tue, Jan 24, 2012 at 02:44:15PM +0100, Jan Kiszka wrote:
>> On 2012-01-24 14:06, Gleb Natapov wrote:
>>> The spec says that during initialization "The edge sense circuit is
>>> reset which means that following initialization an interrupt request
>>> (IR) input must make a low-to-high transition to generate an interrupt",
>>> but currently if edge triggered interrupt is in IRR it is delivered
>>> after i8259 initialization.
>>>
>>> Signed-off-by: Gleb Natapov <gleb@redhat.com>
>>> diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
>>> index b6a7353..81cf4fa 100644
>>> --- a/arch/x86/kvm/i8259.c
>>> +++ b/arch/x86/kvm/i8259.c
>>> @@ -307,6 +307,7 @@ static void pic_ioport_write(void *opaque, u32 addr, u32 val)
>>>  		if (val & 0x10) {
>>>  			s->init4 = val & 1;
>>>  			s->last_irr = 0;
>>> +			s->irr &= s->elcr;
>>
>> Does & elcr make a relevant difference? QEMU simply sets irr to 0. If
>> that's an issue, we need to fix both.
>>
> I saw what QEMU does. It's hard to tell looking at the spec what's more
> correct. I think by zeroing irr we may lose level triggered interrupts
> that happened just before init.

Right. If those are supposed to get through despite init, then it is a
QEMU bug. Will read the spec again as well.

Jan

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