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

[Gleb Natapov <gleb@redhat.com>]

On Tue, Jan 24, 2012 at 02:49:24PM +0100, Jan Kiszka wrote:
> 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.
> 
On real HW they should go through if the IR line is still high.

--
			Gleb.