Thanks for taking a look, David.

On Wed, Mar 04, 2020 at 02:04:10PM -0800, David Miller wrote:

From: Vivek Thampi <redacted>
Date: Fri, 28 Feb 2020 05:32:46 +0000

quoted

Add a PTP clock driver called ptp_vmw, for guests running on VMware ESXi
hypervisor. The driver attaches to a VMware virtual device called
"precision clock" that provides a mechanism for querying host system time.
Similar to existing virtual PTP clock drivers (e.g. ptp_kvm), ptp_vmw
utilizes the kernel's PTP hardware clock API to implement a clock device
that can be used as a reference in Chrony for synchronizing guest time with
host.

The driver is only applicable to x86 guests running in VMware virtual
machines with precision clock virtual device present. It uses a VMware
specific hypercall mechanism to read time from the device.

Reviewed-by: Thomas Hellstrom <redacted>
Signed-off-by: Vivek Thampi <redacted>
---
 Based on feedback, resending patch to include a broader audience.

If it's just providing a read of an accurate timesource, I think it's kinda
pointless to provide a full PTP driver for it.

The point of a PTP driver for this timesource is to provide an interface
that can be consumed by Chrony (and possibly other applications) as a
reference clock for time sync. This is admittedly a very basic first
step providing just PTP_SYS_OFFSET functionality (which gets us to <1us
VM-host time sync). Down the line, I also intend to introduce
cross-timestamping for more precise offsets.

Using the PHC infrastructure seems like a good fit for this, but please
let me know if I'm missing something or misinterpreting your comment.

Thanks.