[PATCH 5.5 147/170] clocksource/drivers/hyper-v: Untangle stimers and timesync from clocksources

[Greg Kroah-Hartman]

From: Yubo Xie <yuboxie@xxxxxxxxxxxxx>

[ Upstream commit 0af3e137c144377fbaf5025ba784ff5ba7ad40c9 ]

hyperv_timer.c exports hyperv_cs, which is used by stimers and the
timesync mechanism.  However, the clocksource dependency is not
needed: these mechanisms only depend on the partition reference
counter (which can be read via a MSR or via the TSC Reference Page).

Introduce the (function) pointer hv_read_reference_counter, as an
embodiment of the partition reference counter read, and export it
in place of the hyperv_cs pointer.  The latter can be removed.

This should clarify that there's no relationship between Hyper-V
stimers & timesync and the Linux clocksource abstractions.  No
functional or semantic change.

Suggested-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Signed-off-by: Andrea Parri <parri.andrea@xxxxxxxxx>
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Signed-off-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20200109160650.16150-2-parri.andrea@xxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/clocksource/hyperv_timer.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -327,7 +327,8 @@ static u64 notrace read_hv_clock_tsc(str
 
 static u64 read_hv_sched_clock_tsc(void)
 {
-	return read_hv_clock_tsc(NULL) - hv_sched_clock_offset;
+	return (read_hv_clock_tsc(NULL) - hv_sched_clock_offset) *
+		(NSEC_PER_SEC / HV_CLOCK_HZ);
 }
 
 static struct clocksource hyperv_cs_tsc = {
@@ -352,7 +353,8 @@ static u64 notrace read_hv_clock_msr(str
 
 static u64 read_hv_sched_clock_msr(void)
 {
-	return read_hv_clock_msr(NULL) - hv_sched_clock_offset;
+	return (read_hv_clock_msr(NULL) - hv_sched_clock_offset) *
+		(NSEC_PER_SEC / HV_CLOCK_HZ);
 }
 
 static struct clocksource hyperv_cs_msr = {