Documentation/virt/kvm/arm/ptp_kvm.rst
.. SPDX-License-Identifier: GPL-2.0
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_IDRetrieve current time information for the specific counter. There are no endianness restrictions.
+---------------------+-------------------------------------------------------+
| Presence: | Optional |
+---------------------+-------------------------------------------------------+
| Calling convention: | HVC32 |
+---------------------+----------+--------------------------------------------+
| Function ID: | (uint32) | 0x86000001 |
+---------------------+----------+----+---------------------------------------+
| Arguments: | (uint32) | R1 | KVM_PTP_VIRT_COUNTER (0) |
| | | +---------------------------------------+
| | | | KVM_PTP_PHYS_COUNTER (1) |
+---------------------+----------+----+---------------------------------------+
| Return Values: | (int32) | R0 | NOT_SUPPORTED (-1) on error, else |
| | | | upper 32 bits of wall clock time |
| +----------+----+---------------------------------------+
| | (uint32) | R1 | Lower 32 bits of wall clock time |
| +----------+----+---------------------------------------+
| | (uint32) | R2 | Upper 32 bits of counter |
| +----------+----+---------------------------------------+
| | (uint32) | R3 | Lower 32 bits of counter |
+---------------------+----------+----+---------------------------------------+