[RFC PATCH 08/45] KVM: arm64: pkvm: Add pkvm_udelay()

[Jean-Philippe Brucker]

Add a simple delay loop for drivers.

This could use more work. It should be possible to insert a wfe and save
power, but I haven't studied whether it is safe to do so with the host
in control of the event stream. The SMMU driver will use wfe anyway for
frequent waits (provided the implementation can send command queue
events).

Signed-off-by: Jean-Philippe Brucker <jean-philippe at linaro.org>
---
 arch/arm64/kvm/hyp/include/nvhe/pkvm.h |  3 ++
 arch/arm64/kvm/hyp/nvhe/setup.c        |  4 +++
 arch/arm64/kvm/hyp/nvhe/timer-sr.c     | 43 ++++++++++++++++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
index 6160d1a34fa2..746dc1c05a8e 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/pkvm.h
@@ -109,4 +109,7 @@ bool kvm_handle_pvm_hvc64(struct kvm_vcpu *vcpu, u64 *exit_code);
 
 struct pkvm_hyp_vcpu *pkvm_mpidr_to_hyp_vcpu(struct pkvm_hyp_vm *vm, u64 mpidr);
 
+int pkvm_timer_init(void);
+void pkvm_udelay(unsigned long usecs);
+
 #endif /* __ARM64_KVM_NVHE_PKVM_H__ */
diff --git a/arch/arm64/kvm/hyp/nvhe/setup.c b/arch/arm64/kvm/hyp/nvhe/setup.c
index 8a357637ce81..629e74c46b35 100644
--- a/arch/arm64/kvm/hyp/nvhe/setup.c
+++ b/arch/arm64/kvm/hyp/nvhe/setup.c
@@ -300,6 +300,10 @@ void __noreturn __pkvm_init_finalise(void)
 	};
 	pkvm_pgtable.mm_ops = &pkvm_pgtable_mm_ops;
 
+	ret = pkvm_timer_init();
+	if (ret)
+		goto out;
+
 	ret = fix_host_ownership();
 	if (ret)
 		goto out;
diff --git a/arch/arm64/kvm/hyp/nvhe/timer-sr.c b/arch/arm64/kvm/hyp/nvhe/timer-sr.c
index 9072e71693ba..202df9003a0d 100644
--- a/arch/arm64/kvm/hyp/nvhe/timer-sr.c
+++ b/arch/arm64/kvm/hyp/nvhe/timer-sr.c
@@ -10,6 +10,10 @@
 
 #include <asm/kvm_hyp.h>
 
+#include <nvhe/pkvm.h>
+
+static u32 timer_freq;
+
 void __kvm_timer_set_cntvoff(u64 cntvoff)
 {
 	write_sysreg(cntvoff, cntvoff_el2);
@@ -46,3 +50,42 @@ void __timer_enable_traps(struct kvm_vcpu *vcpu)
 	val |= CNTHCTL_EL1PCTEN;
 	write_sysreg(val, cnthctl_el2);
 }
+
+static u64 pkvm_ticks_get(void)
+{
+	return __arch_counter_get_cntvct();
+}
+
+#define SEC_TO_US 1000000
+
+int pkvm_timer_init(void)
+{
+	timer_freq = read_sysreg(cntfrq_el0);
+	/*
+	 * TODO: The highest privileged level is supposed to initialize this
+	 * register. But on some systems (which?), this information is only
+	 * contained in the device-tree, so we'll need to find it out some other
+	 * way.
+	 */
+	if (!timer_freq || timer_freq < SEC_TO_US)
+		return -ENODEV;
+	return 0;
+}
+
+
+#define pkvm_time_us_to_ticks(us) ((u64)(us) * timer_freq / SEC_TO_US)
+
+void pkvm_udelay(unsigned long usecs)
+{
+	u64 ticks = pkvm_time_us_to_ticks(usecs);
+	u64 start = pkvm_ticks_get();
+
+	while (true) {
+		u64 cur = pkvm_ticks_get();
+
+		if ((cur - start) >= ticks || cur < start)
+			break;
+		/* TODO wfe */
+		cpu_relax();
+	}
+}
-- 
2.39.0