clocksource: hyper-v: Remove support for stimer interrupts in message mode

In Hyper-V versions prior to WS2016/Win10, Hyper-V synthetic timers
interrupt the guest by delivering a message that is initially handled
by the Linux VMBus driver. Starting with WS2016/Win10, Hyper-V can
deliver stimer interrupts directly to an assigned interrupt vector
without involving the VMBus driver. This is called "Direct Mode".

With the overall removal of Linux support for running on Hyper-V
hosts earlier than WS2016 and Windows 10, it's no longer necessary
to support the legacy message-based delivery. Remove that delivery
mechanism and always use Direct Mode. If for some reason, the
Hyper-V host does not enumerate Direct Mode, output an error
message but continue to run using the LAPIC timer instead of an
stimer.

With these changes, the VMBus driver no longer calls the stimer
interrupt service routine. This removal has a broader benefit in
unblocking the disentangling of VMBus code and stimer code, as
they should be independent of each other. The final disentangling
will come as a follow-on patch set.

Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>

0 files changed, 0 insertions, 0 deletions