arm_arch_timer: Expose event stream status

The arch timer configuration for a CPU might get reset after suspending
said CPU.

In order to reliably use the event stream in the kernel (e.g. for delays),
we keep track of the state where we can safely consider the event stream as
properly configured. After writing to cntkctl, we issue an ISB to ensure
that subsequent delay loops can rely on the event stream being enabled.

Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Danny Lin <danny@kdrag0n.dev>

arch/arm/include/asm/arch_timer.h

@@ -106,6 +106,7 @@ static inline u32 arch_timer_get_cntkctl(void)
 static inline void arch_timer_set_cntkctl(u32 cntkctl)
 {
 	asm volatile("mcr p15, 0, %0, c14, c1, 0" : : "r" (cntkctl));
+	isb();
 }
 
 #endif

arch/arm64/include/asm/arch_timer.h

@@ -103,6 +103,7 @@ static inline u32 arch_timer_get_cntkctl(void)
 static inline void arch_timer_set_cntkctl(u32 cntkctl)
 {
 	asm volatile("msr	cntkctl_el1, %0" : : "r" (cntkctl));
+	isb();
 }
 
 static inline u64 arch_counter_get_cntpct(void)

drivers/clocksource/arm_arch_timer.c

@@ -72,6 +72,8 @@ static bool arch_timer_use_virtual = true;
 static bool arch_timer_c3stop;
 static bool arch_timer_mem_use_virtual;
 
+static cpumask_t evtstrm_available = CPU_MASK_NONE;
+
 /*
  * Architected system timer support.
  */
@@ -307,6 +309,7 @@ static void arch_timer_evtstrm_enable(int divider)
 #ifdef CONFIG_COMPAT
 	compat_elf_hwcap |= COMPAT_HWCAP_EVTSTRM;
 #endif
+	cpumask_set_cpu(smp_processor_id(), &evtstrm_available);
 }
 
 static void arch_timer_configure_evtstream(void)
@@ -408,6 +411,16 @@ u32 arch_timer_get_rate(void)
 	return arch_timer_rate;
 }
 
+bool arch_timer_evtstrm_available(void)
+{
+	/*
+	 * We might get called from a preemptible context. This is fine
+	 * because availability of the event stream should be always the same
+	 * for a preemptible context and context where we might resume a task.
+	 */
+	return cpumask_test_cpu(raw_smp_processor_id(), &evtstrm_available);
+}
+
 static u64 arch_counter_get_cntvct_mem(void)
 {
 	u32 vct_lo, vct_hi, tmp_hi;
@@ -522,6 +535,8 @@ static int arch_timer_cpu_notify(struct notifier_block *self,
 		break;
 	}
 
+	cpumask_clear_cpu(smp_processor_id(), &evtstrm_available);
+
 	return NOTIFY_OK;
 }
 
@@ -534,10 +549,16 @@ static DEFINE_PER_CPU(unsigned long, saved_cntkctl);
 static int arch_timer_cpu_pm_notify(struct notifier_block *self,
 				    unsigned long action, void *hcpu)
 {
-	if (action == CPU_PM_ENTER)
+	if (action == CPU_PM_ENTER) {
 		__this_cpu_write(saved_cntkctl, arch_timer_get_cntkctl());
-	else if (action == CPU_PM_ENTER_FAILED || action == CPU_PM_EXIT)
+
+		cpumask_clear_cpu(smp_processor_id(), &evtstrm_available);
+	} else if (action == CPU_PM_ENTER_FAILED || action == CPU_PM_EXIT) {
 		arch_timer_set_cntkctl(__this_cpu_read(saved_cntkctl));
+
+		if (elf_hwcap & HWCAP_EVTSTRM)
+			cpumask_set_cpu(smp_processor_id(), &evtstrm_available);
+	}
 	return NOTIFY_OK;
 }
 

include/clocksource/arm_arch_timer.h

@@ -57,6 +57,7 @@ extern u32 arch_timer_get_rate(void);
 extern u64 (*arch_timer_read_counter)(void);
 extern struct timecounter *arch_timer_get_timecounter(void);
 
+extern bool arch_timer_evtstrm_available(void);
 #else
 
 static inline u32 arch_timer_get_rate(void)
@@ -74,6 +75,11 @@ static inline struct timecounter *arch_timer_get_timecounter(void)
 	return NULL;
 }
 
+static inline bool arch_timer_evtstrm_available(void)
+{
+	return false;
+}
+
 #endif
 
 #endif