linux-kernel - [PATCH 1/1] drivers: hv: Decouple Hyper-V clock/timer code from VMbus drivers

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Message-Id: <1626220906-22629-1-git-send-email-mikelley@microsoft.com>
Date:   Tue, 13 Jul 2021 17:01:46 -0700
From:   Michael Kelley <mikelley@...rosoft.com>
To:     sthemmin@...rosoft.com, kys@...rosoft.com, wei.liu@...nel.org,
        decui@...rosoft.com, daniel.lezcano@...aro.org, tglx@...utronix.de,
        arnd@...db.de, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org
Cc:     mikelley@...rosoft.com, linux-arch@...r.kernel.org
Subject: [PATCH 1/1] drivers: hv: Decouple Hyper-V clock/timer code from VMbus drivers

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@...rosoft.com>
---
 drivers/clocksource/hyperv_timer.c |  3 ---
 drivers/hv/hv_common.c             | 14 ++++++++++++++
 drivers/hv/hv_util.c               |  5 -----
 include/asm-generic/mshyperv.h     |  2 ++
 include/clocksource/hyperv_timer.h | 11 +++++++++--
 5 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index d6ece7b..ff188ab 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c
@@ -361,9 +361,6 @@ void hv_stimer_global_cleanup(void)
  * 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 3ff8446..e213433 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -215,6 +215,20 @@ bool hv_is_hibernation_supported(void)
 }
 EXPORT_SYMBOL_GPL(hv_is_hibernation_supported);
 
+/*
+ * 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 136576c..835e603 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"
@@ -735,10 +734,6 @@ static int hv_ptp_gettime(struct ptp_clock_info *info, struct timespec64 *ts)
 
 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 2a187fe..f6245fe 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -166,6 +166,8 @@ static inline void vmbus_signal_eom(struct hv_message *msg, u32 old_msg_type)
 extern u32 *hv_vp_index;
 extern u32 hv_max_vp_index;
 
+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 b6774aa..1c566c7 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_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
-- 
1.8.3.1