Index: head/sys/dev/hyperv/vmbus/hv_et.c
===================================================================
--- head/sys/dev/hyperv/vmbus/hv_et.c	(revision 300993)
+++ head/sys/dev/hyperv/vmbus/hv_et.c	(revision 300994)
@@ -1,193 +1,196 @@
 /*-
  * Copyright (c) 2015,2016 Microsoft Corp.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *      notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *      notice, this list of conditions and the following disclaimer in the
  *      documentation and/or other materials provided with the distribution.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  * SUCH DAMAGE.
  */
 
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/bus.h>
 #include <sys/kernel.h>
 #include <sys/module.h>
 #include <sys/proc.h>
 #include <sys/systm.h>
 #include <sys/smp.h>
 #include <sys/time.h>
 #include <sys/timeet.h>
 
 #include <dev/hyperv/vmbus/hyperv_reg.h>
 #include <dev/hyperv/vmbus/hyperv_var.h>
 #include <dev/hyperv/vmbus/vmbus_var.h>
 
 #define VMBUS_ET_NAME			"hvet"
 
 #define MSR_HV_STIMER0_CFG_SINT		\
 	((((uint64_t)VMBUS_SINT_TIMER) << MSR_HV_STIMER_CFG_SINT_SHIFT) & \
 	 MSR_HV_STIMER_CFG_SINT_MASK)
 
 /*
  * Two additionally required features:
  * - SynIC is needed for interrupt generation.
  * - Time reference counter is needed to set ABS reference count to
  *   STIMER0_COUNT.
  */
 #define CPUID_HV_ET_MASK		(CPUID_HV_MSR_TIME_REFCNT |	\
 					 CPUID_HV_MSR_SYNIC |		\
 					 CPUID_HV_MSR_SYNTIMER)
 
 static struct eventtimer	vmbus_et;
 
 static __inline uint64_t
 hyperv_sbintime2count(sbintime_t time)
 {
 	struct timespec val;
 
 	val = sbttots(time);
 	return (val.tv_sec * HYPERV_TIMER_FREQ) +
 	    (val.tv_nsec / HYPERV_TIMER_NS_FACTOR);
 }
 
 static int
 vmbus_et_start(struct eventtimer *et __unused, sbintime_t first,
     sbintime_t period __unused)
 {
 	uint64_t current;
 
 	current = rdmsr(MSR_HV_TIME_REF_COUNT);
 	current += hyperv_sbintime2count(first);
 	wrmsr(MSR_HV_STIMER0_COUNT, current);
 
 	return (0);
 }
 
 void
 vmbus_et_intr(struct trapframe *frame)
 {
 	struct trapframe *oldframe;
 	struct thread *td;
 
 	if (vmbus_et.et_active) {
 		td = curthread;
 		td->td_intr_nesting_level++;
 		oldframe = td->td_intr_frame;
 		td->td_intr_frame = frame;
 		vmbus_et.et_event_cb(&vmbus_et, vmbus_et.et_arg);
 		td->td_intr_frame = oldframe;
 		td->td_intr_nesting_level--;
 	}
 }
 
 static void
 vmbus_et_identify(driver_t *driver, device_t parent)
 {
 	if (device_get_unit(parent) != 0 ||
 	    device_find_child(parent, VMBUS_ET_NAME, -1) != NULL ||
 	    (hyperv_features & CPUID_HV_ET_MASK) != CPUID_HV_ET_MASK)
 		return;
 
 	device_add_child(parent, VMBUS_ET_NAME, -1);
 }
 
 static int
 vmbus_et_probe(device_t dev)
 {
+	if (resource_disabled(VMBUS_ET_NAME, 0))
+		return (ENXIO);
+
 	device_set_desc(dev, "Hyper-V event timer");
 
 	return (BUS_PROBE_NOWILDCARD);
 }
 
 static void
 vmbus_et_config(void *arg __unused)
 {
 	/*
 	 * Make sure that STIMER0 is really disabled before writing
 	 * to STIMER0_CONFIG.
 	 *
 	 * "Writing to the configuration register of a timer that
 	 *  is already enabled may result in undefined behaviour."
 	 */
 	for (;;) {
 		uint64_t val;
 
 		/* Stop counting, and this also implies disabling STIMER0 */
 		wrmsr(MSR_HV_STIMER0_COUNT, 0);
 
 		val = rdmsr(MSR_HV_STIMER0_CONFIG);
 		if ((val & MSR_HV_STIMER_CFG_ENABLE) == 0)
 			break;
 		cpu_spinwait();
 	}
 	wrmsr(MSR_HV_STIMER0_CONFIG,
 	    MSR_HV_STIMER_CFG_AUTOEN | MSR_HV_STIMER0_CFG_SINT);
 }
 
 static int
 vmbus_et_attach(device_t dev)
 {
 	/* TODO: use independent IDT vector */
 
 	vmbus_et.et_name = "Hyper-V";
 	vmbus_et.et_flags = ET_FLAGS_ONESHOT | ET_FLAGS_PERCPU;
 	vmbus_et.et_quality = 1000;
 	vmbus_et.et_frequency = HYPERV_TIMER_FREQ;
 	vmbus_et.et_min_period = (0x00000001ULL << 32) / HYPERV_TIMER_FREQ;
 	vmbus_et.et_max_period = (0xfffffffeULL << 32) / HYPERV_TIMER_FREQ;
 	vmbus_et.et_start = vmbus_et_start;
 
 	/*
 	 * Delay a bit to make sure that MSR_HV_TIME_REF_COUNT will
 	 * not return 0, since writing 0 to STIMER0_COUNT will disable
 	 * STIMER0.
 	 */
 	DELAY(100);
 	smp_rendezvous(NULL, vmbus_et_config, NULL, NULL);
 
 	return (et_register(&vmbus_et));
 }
 
 static int
 vmbus_et_detach(device_t dev)
 {
 	return (et_deregister(&vmbus_et));
 }
 
 static device_method_t vmbus_et_methods[] = {
 	DEVMETHOD(device_identify,	vmbus_et_identify),
 	DEVMETHOD(device_probe,		vmbus_et_probe),
 	DEVMETHOD(device_attach,	vmbus_et_attach),
 	DEVMETHOD(device_detach,	vmbus_et_detach),
 
 	DEVMETHOD_END
 };
 
 static driver_t vmbus_et_driver = {
 	VMBUS_ET_NAME,
 	vmbus_et_methods,
 	0
 };
 
 static devclass_t vmbus_et_devclass;
 DRIVER_MODULE(hv_et, vmbus, vmbus_et_driver, vmbus_et_devclass, NULL, NULL);
 MODULE_VERSION(hv_et, 1);