When running on Hyper-V, make use of its timecounter as delay func in case

we're still using the i8254 for that.  On Hyper-V Gen 2 VMs there is no
i8254 we can trust, so we need some kind of fallback, especially if there
is no TSC either.

Discussed with the hackroom
ok kettenis@

1 files changed, 12 insertions, 0 deletions

diff --git a/sys/dev/pv/hyperv.c b/sys/dev/pv/hyperv.c
index de753ccbfc9..dcebd3ae681 100644
--- a/sys/dev/pv/hyperv.c
+++ b/sys/dev/pv/hyperv.c
@@ -349,6 +349,18 @@ hv_gettime(struct timecounter *tc)
 	return (now);
 }
 
+void
+hv_delay(int usecs)
+{
+	uint64_t interval, start;
+
+	/* 10 MHz fixed frequency */
+	interval = (uint64_t)usecs * 10;
+	start = rdmsr(MSR_HV_TIME_REF_COUNT);
+	while (rdmsr(MSR_HV_TIME_REF_COUNT) - start < interval)
+		CPU_BUSY_CYCLE();
+}
+
 int
 hv_init_hypercall(struct hv_softc *sc)
 {