Drivers: hv: vmbus: Don't wait for the ACPI device upon initialization

Waiting to 5 seconds in case of missing VMBus ACPI device is redundant as the
device is either present already or won't be available at all.

This patch enforces synchronous probing to make sure the bus traversal,
happening upon driver registering will either find the device (if present) or
not spend any additional time if device is absent.

Signed-off-by: Stanislav Kinsburskiy <stanislav.kinsburskiy@gmail.com>
CC: "K. Y. Srinivasan" <kys@microsoft.com>
CC: Haiyang Zhang <haiyangz@microsoft.com>
CC: Stephen Hemminger <sthemmin@microsoft.com>
CC: Wei Liu <wei.liu@kernel.org>
CC: Dexuan Cui <decui@microsoft.com>
CC: linux-hyperv@vger.kernel.org
CC: linux-kernel@vger.kernel.org
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Dexuan Cui <decui@microsoft.com>
Link: https://lore.kernel.org/r/166378554568.581670.1124852716698789244.stgit@skinsburskii-cloud-desktop.internal.cloudapp.net
Signed-off-by: Wei Liu <wei.liu@kernel.org>

Author: skinsbursky

drivers/hv/vmbus_drv.c

@@ -46,8 +46,6 @@ struct vmbus_dynid {
 
 static struct acpi_device  *hv_acpi_dev;
 
-static struct completion probe_event;
-
 static int hyperv_cpuhp_online;
 
 static void *hv_panic_page;
@@ -2467,7 +2465,6 @@ static int vmbus_acpi_add(struct acpi_device *device)
 	ret_val = 0;
 
 acpi_walk_err:
-	complete(&probe_event);
 	if (ret_val)
 		vmbus_acpi_remove(device);
 	return ret_val;
@@ -2646,6 +2643,7 @@ static struct acpi_driver vmbus_acpi_driver = {
 		.remove = vmbus_acpi_remove,
 	},
 	.drv.pm = &vmbus_bus_pm,
+	.drv.probe_type = PROBE_FORCE_SYNCHRONOUS,
 };
 
 static void hv_kexec_handler(void)
@@ -2718,16 +2716,14 @@ static struct syscore_ops hv_synic_syscore_ops = {
 
 static int __init hv_acpi_init(void)
 {
-	int ret, t;
+	int ret;
 
 	if (!hv_is_hyperv_initialized())
 		return -ENODEV;
 
 	if (hv_root_partition)
 		return 0;
 
-	init_completion(&probe_event);
-
 	/*
 	 * Get ACPI resources first.
 	 */
@@ -2736,9 +2732,8 @@ static int __init hv_acpi_init(void)
 	if (ret)
 		return ret;
 
-	t = wait_for_completion_timeout(&probe_event, 5*HZ);
-	if (t == 0) {
-		ret = -ETIMEDOUT;
+	if (!hv_acpi_dev) {
+		ret = -ENODEV;
 		goto cleanup;
 	}