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>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 4c943eabacc3..3324d90038e4 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -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: