summaryrefslogtreecommitdiffstats
path: root/Documentation/virt/kvm/arm/ptp_kvm.rst
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/virt/kvm/arm/ptp_kvm.rst')
-rw-r--r--Documentation/virt/kvm/arm/ptp_kvm.rst25
1 files changed, 25 insertions, 0 deletions
diff --git a/Documentation/virt/kvm/arm/ptp_kvm.rst b/Documentation/virt/kvm/arm/ptp_kvm.rst
new file mode 100644
index 000000000..aecdc80dd
--- /dev/null
+++ b/Documentation/virt/kvm/arm/ptp_kvm.rst
@@ -0,0 +1,25 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+PTP_KVM support for arm/arm64
+=============================
+
+PTP_KVM is used for high precision time sync between host and guests.
+It relies on transferring the wall clock and counter value from the
+host to the guest using a KVM-specific hypercall.
+
+* ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID: 0x86000001
+
+This hypercall uses the SMC32/HVC32 calling convention:
+
+ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID
+ ============== ======== =====================================
+ Function ID: (uint32) 0x86000001
+ Arguments: (uint32) KVM_PTP_VIRT_COUNTER(0)
+ KVM_PTP_PHYS_COUNTER(1)
+ Return Values: (int32) NOT_SUPPORTED(-1) on error, or
+ (uint32) Upper 32 bits of wall clock time (r0)
+ (uint32) Lower 32 bits of wall clock time (r1)
+ (uint32) Upper 32 bits of counter (r2)
+ (uint32) Lower 32 bits of counter (r3)
+ Endianness: No Restrictions.
+ ============== ======== =====================================