.. 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``
----------------------------------------
Retrieve 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 |
+---------------------+----------+----+---------------------------------------+
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