[Qemu-devel] [PATCH KVM v2 2/4] KVM: additional i8254 output fixes

[Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>]

Make git_get_out() consistent with spec.  Currently pit_get_out()
doesn't affect IRQ0, but it can be read by the guest in other ways.
This makes it consistent with proposed changes in qemu's i8254 model
as well.

See http://bochs.sourceforge.net/techspec/intel-82c54-timer.pdf.gz
or search the net for 23124406.pdf.

Signed-off-by: Matthew Ogilvie <mmogilvi_qemu@miniinfo.net>
---
 arch/x86/kvm/i8254.c | 44 ++++++++++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index cd4ec60..fd38938 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -144,6 +144,10 @@ static int pit_get_count(struct kvm *kvm, int channel)
 
 	WARN_ON(!mutex_is_locked(&kvm->arch.vpit->pit_state.lock));
 
+	/* FIXME: Add some way to represent a paused timer and return
+	 *   the paused-at counter value, to better model gate pausing,
+	 *   "wait until next CLK pulse to load counter" logic, etc.
+	 */
 	t = kpit_elapsed(kvm, c, channel);
 	d = muldiv64(t, KVM_PIT_FREQ, NSEC_PER_SEC);
 
@@ -155,8 +159,7 @@ static int pit_get_count(struct kvm *kvm, int channel)
 		counter = (c->count - d) & 0xffff;
 		break;
 	case 3:
-		/* XXX: may be incorrect for odd counts */
-		counter = c->count - (mod_64((2 * d), c->count));
+		counter = (c->count - (mod_64((2 * d), c->count))) & 0xfffe;
 		break;
 	default:
 		counter = c->count - mod_64(d, c->count);
@@ -180,20 +183,18 @@ static int pit_get_out(struct kvm *kvm, int channel)
 	switch (c->mode) {
 	default:
 	case 0:
-		out = (d >= c->count);
-		break;
 	case 1:
-		out = (d < c->count);
+		out = (d >= c->count);
 		break;
 	case 2:
-		out = ((mod_64(d, c->count) == 0) && (d != 0));
+		out = (mod_64(d, c->count) != (c->count - 1) || c->gate == 0);
 		break;
 	case 3:
-		out = (mod_64(d, c->count) < ((c->count + 1) >> 1));
+		out = (mod_64(d, c->count) < ((c->count + 1) >> 1) || c->gate == 0);
 		break;
 	case 4:
 	case 5:
-		out = (d == c->count);
+		out = (d != c->count);
 		break;
 	}
 
@@ -367,7 +368,7 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
 
 	/*
 	 * The largest possible initial count is 0; this is equivalent
-	 * to 216 for binary counting and 104 for BCD counting.
+	 * to pow(2,16) for binary counting and pow(10,4) for BCD counting.
 	 */
 	if (val == 0)
 		val = 0x10000;
@@ -376,6 +377,26 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
 
 	if (channel != 0) {
 		ps->channels[channel].count_load_time = ktime_get();
+
+		/* In gate-triggered one-shot modes,
+		 * indirectly model some pit_get_out()
+		 * cases by setting the load time way
+		 * back until gate-triggered.
+		 * (Generally only affects reading status
+		 * from channel 2 speaker,
+		 * due to hard-wired gates on other
+		 * channels.)
+		 *
+		 * FIXME: This might be redesigned if a paused
+		 * timer state is added for pit_get_count().
+		 */
+		if (ps->channels[channel].mode == 1 ||
+		    ps->channels[channel].mode == 5) {
+	            u64 delta = muldiv64(val+2, NSEC_PER_SEC, KVM_PIT_FREQ);
+		    ps->channels[channel].count_load_time =
+                            ktime_sub(ps->channels[channel].count_load_time,
+                                      ns_to_ktime(delta));
+		}
 		return;
 	}
 
@@ -383,7 +404,6 @@ 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 0:
-	case 1:
         /* FIXME: enhance mode 4 precision */
 	case 4:
 		create_pit_timer(kvm, val, 0);
@@ -393,6 +413,10 @@ static void pit_load_count(struct kvm *kvm, int channel, u32 val)
 		create_pit_timer(kvm, val, 1);
 		break;
 	default:
+		/* Modes 1 and 5 are triggered by gate leading edge,
+		 * but channel 0's gate is hard-wired high and has
+		 * no edges (on normal real hardware).
+		 */
 		destroy_pit_timer(kvm->arch.vpit);
 	}
 }
-- 
1.7.10.2.484.gcd07cc5