[RFC PATCH 4/4] ARM: arch_timers: dynamic switch to physical timer and virtual timer offloading

[Marc Zyngier]

In an environment supporting virtualization (KVM), the virtual timer
is reserved to the guests, while we rely on the physical timer for
the host.

For this, we need to:
- switch the host CPUs from the virtual timer to the physical one
- provide an interrupt handler that is called by the virtual
  timer's interrupt handler.

The new function arch_timer_switch_to_phys() performs this task.

Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
---
 arch/arm/include/asm/arch_timer.h |    6 +++++
 arch/arm/kernel/arch_timer.c      |   49 +++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/arch/arm/include/asm/arch_timer.h b/arch/arm/include/asm/arch_timer.h
index 72c6822..7cd1e27 100644
--- a/arch/arm/include/asm/arch_timer.h
+++ b/arch/arm/include/asm/arch_timer.h
@@ -2,11 +2,13 @@
 #define __ASMARM_ARCH_TIMER_H
 
 #include <linux/clocksource.h>
+#include <linux/interrupt.h>
 
 #ifdef CONFIG_ARM_ARCH_TIMER
 int arch_timer_of_register(void);
 int arch_timer_sched_clock_init(void);
 struct timecounter *arch_timer_get_timecounter(void);
+void arch_timer_switch_to_phys(irq_handler_t);
 #else
 static inline int arch_timer_of_register(void)
 {
@@ -22,6 +24,10 @@ static inline struct timecounter *arch_timer_get_timecounter(void)
 {
 	return NULL;
 }
+
+static inline void arch_timer_switch_to_phys(irq_handler_t handler)
+{
+}
 #endif
 
 #endif
diff --git a/arch/arm/kernel/arch_timer.c b/arch/arm/kernel/arch_timer.c
index 4473f66..1bb632a 100644
--- a/arch/arm/kernel/arch_timer.c
+++ b/arch/arm/kernel/arch_timer.c
@@ -50,6 +50,8 @@ struct arch_timer_reg_ops {
 
 static struct arch_timer_reg_ops __percpu **arch_timer_reg_ops;
 
+static irq_handler_t arch_timer_virt_external_handler;
+
 /*
  * Architected system timer support.
  */
@@ -204,6 +206,19 @@ static irqreturn_t arch_timer_handler(int irq, void *dev_id)
 
 static irqreturn_t arch_timer_virt_handler(int irq, void *dev_id)
 {
+	if (arch_timer_virt_external_handler) {
+		unsigned long ctrl;
+
+		ctrl = arch_timer_virt_reg_read(ARCH_TIMER_REG_CTRL);
+		if (ctrl & ARCH_TIMER_CTRL_IT_STAT) {
+			ctrl |= ARCH_TIMER_CTRL_IT_MASK;
+			arch_timer_virt_reg_write(ARCH_TIMER_REG_CTRL, ctrl);
+			return arch_timer_virt_external_handler(irq, NULL);
+		}
+
+		return IRQ_NONE;
+	}
+
 	return arch_timer_handler(irq, dev_id);
 }
 
@@ -509,3 +524,37 @@ int __init arch_timer_sched_clock_init(void)
 	setup_sched_clock(arch_counter_get_cnt32, 32, arch_timer_rate);
 	return 0;
 }
+
+static void arch_timer_switch_cpu_to_phys(void *dummy)
+{
+	u32 cvall, cvalh, val;
+
+	pr_info("Switching CPU%d to physical timer\n", smp_processor_id());
+
+	asm volatile("mrrc p15, 3, %0, %1, c14	\n" /* Read CNTV_CVAL */
+		     "mcrr p15, 2, %0, %1, c14	\n" /* Write CNTP_CVAL */
+		     : "=r" (cvall), "=r" (cvalh));
+
+	isb();
+	
+	val = arch_timer_virt_reg_read(ARCH_TIMER_REG_CTRL);
+	arch_timer_virt_reg_write(ARCH_TIMER_REG_CTRL,
+				  val & ~ARCH_TIMER_CTRL_ENABLE);
+	arch_timer_phys_reg_write(ARCH_TIMER_REG_CTRL, val);
+	*__this_cpu_ptr(arch_timer_reg_ops) = &arch_timer_phys_ops;
+}
+
+void arch_timer_switch_to_phys(irq_handler_t handler)
+{
+	int cpu;
+
+	if (!arch_timer_use_virtual)
+		return;
+
+	for_each_online_cpu(cpu)
+		smp_call_function_single(cpu, arch_timer_switch_cpu_to_phys,
+					 NULL, 1);
+
+	arch_timer_use_virtual = false;
+	arch_timer_virt_external_handler = handler;
+}
-- 
1.7.10.3