[PATCH 29/41] drivers: hv: Decouple Hyper-V clock/timer code from VMbus drivers

[Tim Gardner]

From: Michael Kelley <mikelley at microsoft.com>

BugLink: https://bugs.launchpad.net/bugs/1949770

Hyper-V clock/timer code in hyperv_timer.c is mostly independent from
other VMbus drivers, but building for ARM64 without hyperv_timer.c
shows some remaining entanglements.  A default implementation of
hv_read_reference_counter can just read a Hyper-V synthetic register
and be independent of hyperv_timer.c, so move this code out and into
hv_common.c. Then it can be used by the timesync driver even if
hyperv_timer.c isn't built on a particular architecture.  If
hyperv_timer.c *is* built, it can override with a faster implementation.

Also provide stubs for stimer functions called by the VMbus driver when
hyperv_timer.c isn't built.

No functional changes.

Signed-off-by: Michael Kelley <mikelley at microsoft.com>
Link: https://lore.kernel.org/r/1626220906-22629-1-git-send-email-mikelley@microsoft.com
Signed-off-by: Wei Liu <wei.liu at kernel.org>
(backported from commit 31e5e64694cf9879e63b2802007fa934f4131126)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
[rtg - minor context differences]
---
 drivers/clocksource/hyperv_timer.c |  3 ---
 drivers/hv/hv_common.c             | 14 ++++++++++++++
 drivers/hv/hv_util.c               |  5 -----
 include/asm-generic/mshyperv.h     |  1 +
 include/clocksource/hyperv_timer.h | 11 +++++++++--
 5 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index d1510d43211b..169f19ec5f2a 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -361,9 +361,6 @@ EXPORT_SYMBOL_GPL(hv_stimer_global_cleanup);
  * Hyper-V and 32-bit x86.  The TSC reference page version is preferred.
  */
 
-u64 (*hv_read_reference_counter)(void);
-EXPORT_SYMBOL_GPL(hv_read_reference_counter);
-
 static union {
 	struct ms_hyperv_tsc_page page;
 	u8 reserved[PAGE_SIZE];
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index cac9c6bfc653..8caffed7261a 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -204,6 +204,20 @@ bool hv_query_ext_cap(u64 cap_query)
 }
 EXPORT_SYMBOL_GPL(hv_query_ext_cap);
 
+/*
+ * Default function to read the Hyper-V reference counter, independent
+ * of whether Hyper-V enlightened clocks/timers are being used. But on
+ * architectures where it is used, Hyper-V enlightenment code in
+ * hyperv_timer.c may override this function.
+ */
+static u64 __hv_read_ref_counter(void)
+{
+	return hv_get_register(HV_REGISTER_TIME_REF_COUNT);
+}
+
+u64 (*hv_read_reference_counter)(void) = __hv_read_ref_counter;
+EXPORT_SYMBOL_GPL(hv_read_reference_counter);
+
 /* These __weak functions provide default "no-op" behavior and
  * may be overridden by architecture specific versions. Architectures
  * for which the default "no-op" behavior is sufficient can leave
diff --git a/drivers/hv/hv_util.c b/drivers/hv/hv_util.c
index 1b914e418e41..83d6a1d80172 100644
--- a/drivers/hv/hv_util.c
+++ b/drivers/hv/hv_util.c
@@ -17,7 +17,6 @@
 #include <linux/hyperv.h>
 #include <linux/clockchips.h>
 #include <linux/ptp_clock_kernel.h>
-#include <clocksource/hyperv_timer.h>
 #include <asm/mshyperv.h>
 
 #include "hyperv_vmbus.h"
@@ -681,10 +680,6 @@ static struct ptp_clock *hv_ptp_clock;
 
 static int hv_timesync_init(struct hv_util_service *srv)
 {
-	/* TimeSync requires Hyper-V clocksource. */
-	if (!hv_read_reference_counter)
-		return -ENODEV;
-
 	spin_lock_init(&host_ts.lock);
 
 	INIT_WORK(&adj_time_work, hv_set_host_time);
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index f34a7f7be4e9..d59be5fb5315 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -164,6 +164,7 @@ extern u32 *hv_vp_index;
 extern u32 hv_max_vp_index;
 
 extern void  __percpu  **hyperv_pcpu_input_arg;
+extern u64 (*hv_read_reference_counter)(void);
 
 /* Sentinel value for an uninitialized entry in hv_vp_index array */
 #define VP_INVAL	U32_MAX
diff --git a/include/clocksource/hyperv_timer.h b/include/clocksource/hyperv_timer.h
index b6774aa5a4b8..b3f5d73ae1d6 100644
--- a/include/clocksource/hyperv_timer.h
+++ b/include/clocksource/hyperv_timer.h
@@ -20,6 +20,8 @@
 #define HV_MAX_MAX_DELTA_TICKS 0xffffffff
 #define HV_MIN_DELTA_TICKS 1
 
+#ifdef CONFIG_HYPERV_TIMER
+
 /* Routines called by the VMbus driver */
 extern int hv_stimer_alloc(bool have_percpu_irqs);
 extern int hv_stimer_cleanup(unsigned int cpu);
@@ -28,8 +30,6 @@ extern void hv_stimer_legacy_cleanup(unsigned int cpu);
 extern void hv_stimer_global_cleanup(void);
 extern void hv_stimer0_isr(void);
 
-#ifdef CONFIG_HYPERV_TIMER
-extern u64 (*hv_read_reference_counter)(void);
 extern void hv_init_clocksource(void);
 
 extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
@@ -100,6 +100,13 @@ static inline u64 hv_read_tsc_page_tsc(const struct ms_hyperv_tsc_page *tsc_pg,
 {
 	return U64_MAX;
 }
+
+static inline int hv_stimer_cleanup(unsigned int cpu) { return 0; }
+static inline void hv_stimer_legacy_init(unsigned int cpu, int sint) {}
+static inline void hv_stimer_legacy_cleanup(unsigned int cpu) {}
+static inline void hv_stimer_global_cleanup(void) {}
+static inline void hv_stimer0_isr(void) {}
+
 #endif /* CONFIG_HYPERV_TIMER */
 
 #endif
-- 
2.33.1