dm: vhpet: add vHPET support

vHPET is used as a source of system timer by UEFI (e.g. OVMF).

This provides an alternative to using vPIT, which OVMF assumes is always
connected to vPIC.

This is ported from Bhyve, with a few changes:

- move to user space, using acrn_timer
- enable timers only when necessary

Origin: FreeBSD
License: BSD-3-Clause
URL: https://svnweb.freebsd.org/
commit: 326257
Purpose: Adding vHPET support.
Maintained-by: External

Tracked-On: #2319
Signed-off-by: Peter Fang <peter.fang@intel.com>
Acked-by: Anthony Xu <anthony.xu@intel.com>

devicemodel/include/timer.h

@@ -6,6 +6,8 @@
 #ifndef _TIMER_H_
 #define _TIMER_H_
 
+#include <sys/param.h>
+
 struct acrn_timer {
 	int32_t fd;
 	int32_t clockid;
@@ -26,4 +28,28 @@ acrn_timer_settime_abs(struct acrn_timer *timer,
 int32_t
 acrn_timer_gettime(struct acrn_timer *timer, struct itimerspec *cur_value);
 
+#define NS_PER_SEC	(1000000000ULL)
+
+static inline uint64_t
+ts_to_ticks(const uint32_t freq, const struct timespec *const ts)
+{
+	uint64_t tv_sec_ticks, tv_nsec_ticks;
+
+	tv_sec_ticks = ts->tv_sec * freq;
+	tv_nsec_ticks = (ts->tv_nsec * freq) / NS_PER_SEC;
+
+	return tv_sec_ticks + tv_nsec_ticks;
+}
+
+static inline void
+ticks_to_ts(const uint32_t freq, const uint64_t ticks,
+		struct timespec *const ts)
+{
+	uint64_t ns;
+
+	ns = howmany(ticks * NS_PER_SEC, freq);
+
+	ts->tv_sec = ns / NS_PER_SEC;
+	ts->tv_nsec = ns % NS_PER_SEC;
+}
 #endif /* _VTIMER_ */