x86/HPET: don't arbitrarily cap delta in reprogram_hpet_evt_channel()

There's no reason to set an arbitrary upper bound of 10 seconds. We can
simply set the comparator such that it'll take a whole cycle through all
32-bit values until the next interrupt would be raised. (For an extremely
fast-running HPET [400 MHz and up] 10 seconds would also be too long.)

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

xen/arch/x86/hpet.c

@@ -23,7 +23,6 @@
 #include <asm/irq-vectors.h>
 #include <asm/msi.h>
 
-#define MAX_DELTA_NS MILLISECS(10*1000)
 #define MIN_DELTA_NS MICROSECS(20)
 
 #define HPET_EVT_USED_BIT    0
@@ -164,10 +163,15 @@ static int reprogram_hpet_evt_channel(
 
     ASSERT(expire != STIME_MAX);
 
-    delta = min_t(int64_t, delta, MAX_DELTA_NS);
     delta = max_t(int64_t, delta, MIN_DELTA_NS);
     delta = ns2ticks(delta, ch->shift, ch->mult);
 
+    if ( delta > UINT32_MAX )
+    {
+        hpet_write32(hpet_read32(HPET_COUNTER), HPET_Tn_CMP(ch->idx));
+        return 0;
+    }
+
     do {
         ret = hpet_next_event(delta, ch->idx);
         delta += delta;