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

[Matthew Ogilvie]

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 <address@hidden>
---
 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