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KVM: PIT: support mode 4 

The in-kernel PIT emulation ignores pending timers if operating under
mode 4, which for example DragonFlyBSD uses (and Plan9 too, apparently).

Mode 4 seems to be similar to one-shot mode, other than the fact that it
starts counting after the next CLK pulse once programmed, while mode 1
starts counting immediately, so add a FIXME to enhance precision.

Fixes sourceforge bug 1952988.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Acked-by: Sheng Yang <sheng.yang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Marcelo Tosatti 2008-04-30 13:23:54 -03:00 committed by Avi Kivity
parent dc7457ea52
commit ece15babfa
1 changed files with 2 additions and 0 deletions
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arch/x86/kvm/i8254.c
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@ -288,6 +288,8 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
* mode 1 is one shot, mode 2 is period, otherwise del timer */
switch (ps->channels[0].mode) {
case 1:
/* FIXME: enhance mode 4 precision */
case 4:
create_pit_timer(&ps->pit_timer, val, 0);
break;
case 2: