Re: [PATCH v2 10/10] clocksource/drivers/hyper-v: Move handling of STIMER0 interrupts

STIMER0 interrupts are most naturally modeled as per-cpu IRQs. But
because x86/x64 doesn't have per-cpu IRQs, the core STIMER0 interrupt
handling machinery is done in code under arch/x86 and Linux IRQs are
not used. Adding support for ARM64 means adding equivalent code
using per-cpu IRQs under arch/arm64.

A better model is to treat per-cpu IRQs as the normal path (which it is
for modern architectures), and the x86/x64 path as the exception. Do this
by incorporating standard Linux per-cpu IRQ allocation into the main
SITMER0 driver code, and bypass it in the x86/x64 exception case. For
x86/x64, special case code is retained under arch/x86, but no STIMER0
interrupt handling code is needed under arch/arm64.

No functional change.

Signed-off-by: Michael Kelley <redacted>
---
 arch/x86/hyperv/hv_init.c          |   2 +-
 arch/x86/include/asm/mshyperv.h    |   4 -
 arch/x86/kernel/cpu/mshyperv.c     |  10 +--
 drivers/clocksource/hyperv_timer.c | 180 ++++++++++++++++++++++++++-----------
 include/asm-generic/mshyperv.h     |   5 --
 include/clocksource/hyperv_timer.h |   3 +-
 6 files changed, 132 insertions(+), 72 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 9af4f8a..9d10025 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c

@@ -327,7 +327,7 @@ static void __init hv_stimer_setup_percpu_clockev(void)
 	 * Ignore any errors in setting up stimer clockevents
 	 * as we can run with the LAPIC timer as a fallback.
 	 */
-	(void)hv_stimer_alloc();
+	(void)hv_stimer_alloc(false);
 
 	/*
 	 * Still register the LAPIC timer, because the direct-mode STIMER is

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 5433312..6d4891b 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h

@@ -31,10 +31,6 @@ static inline u64 hv_get_register(unsigned int reg)
 
 void hyperv_vector_handler(struct pt_regs *regs);
 
-static inline void hv_enable_stimer0_percpu_irq(int irq) {}
-static inline void hv_disable_stimer0_percpu_irq(int irq) {}
-
-
 #if IS_ENABLED(CONFIG_HYPERV)
 extern int hyperv_init_cpuhp;
 

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 41fd84a..cebed53 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c

@@ -90,21 +90,17 @@ void hv_remove_vmbus_handler(void)
 	set_irq_regs(old_regs);
 }
 
-int hv_setup_stimer0_irq(int *irq, int *vector, void (*handler)(void))
+/* For x86/x64, override weak placeholders in hyperv_timer.c */
+void hv_setup_stimer0_handler(void (*handler)(void))
 {
-	*vector = HYPERV_STIMER0_VECTOR;
-	*irq = -1;   /* Unused on x86/x64 */
 	hv_stimer0_handler = handler;
-	return 0;
 }
-EXPORT_SYMBOL_GPL(hv_setup_stimer0_irq);
 
-void hv_remove_stimer0_irq(int irq)
+void hv_remove_stimer0_handler(void)
 {
 	/* We have no way to deallocate the interrupt gate */
 	hv_stimer0_handler = NULL;
 }
-EXPORT_SYMBOL_GPL(hv_remove_stimer0_irq);
 
 void hv_setup_kexec_handler(void (*handler)(void))
 {

diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
index cdb8e0c..b2bf5e5 100644
--- a/drivers/clocksource/hyperv_timer.c
+++ b/drivers/clocksource/hyperv_timer.c

@@ -18,6 +18,9 @@
 #include <linux/sched_clock.h>
 #include <linux/mm.h>
 #include <linux/cpuhotplug.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/acpi.h>
 #include <clocksource/hyperv_timer.h>
 #include <asm/hyperv-tlfs.h>
 #include <asm/mshyperv.h>

@@ -43,14 +46,13 @@
  */
 static bool direct_mode_enabled;
 
-static int stimer0_irq;
-static int stimer0_vector;
+static int stimer0_irq = -1;
+static long __percpu *stimer0_evt;