[Xen-devel] [PATCH v2 06/10] hvm/hpet: comparator can only change when master clock is enabled.

[Don Slutz <dslutz@xxxxxxxxxxx>]

This is based on software-developers-hpet-spec-1-0a.pdf saying:

When the main counter value matches the value in the timer's
comparator register, an interrupt can be generated.  The hardware
will then automatically increase the value in the compare register
by the last value written to that register.

And since interrupt can only be generated when the master clock
is enabled.

Signed-off-by: Don Slutz <dslutz@xxxxxxxxxxx>
---
 xen/arch/x86/hvm/hpet.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/hpet.c b/xen/arch/x86/hvm/hpet.c
index bcd2778..c0529e7 100644
--- a/xen/arch/x86/hvm/hpet.c
+++ b/xen/arch/x86/hvm/hpet.c
@@ -90,7 +90,7 @@ static uint64_t hpet_get_comparator(HPETState *h, unsigned 
int tn,
     uint64_t elapsed;
 
     comparator = h->hpet.comparator64[tn];
-    if ( timer_is_periodic(h, tn) )
+    if ( hpet_enabled(h) && timer_is_periodic(h, tn) )
     {
         /* update comparator by number of periods elapsed since last update */
         uint64_t period = h->hpet.period[tn];
-- 
1.8.4


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