Revert "staging: vc04_services: vchiq_core: Stop kthreads on shutdown"

This reverts commit d9c60badccc183eb971e0941bb86f9475d4b9551.

It has been reported that stopping kthreads corrupts the VC04 firmware
and creates issues at boot time [1].

A fix-up version of this patch
bac670144384 ("staging: vc04_services: Stop kthreads on .remove") [2]
was also attempted but it also doesn't properly fix the TODO
(i.e. clean module unload) and similar errors were observed when
stopping these khthreads on RaspberryPi 3.

Hence, revert the entire patch for now since it is not very clear why
stopping the kthreads breaks the firmware.

[1]: https://lore.kernel.org/linux-staging/[e-mail]/t/#me90b9a9bc91599f18cd65ceb7eedd40e5fee0cdd

[2]: https://lore.kernel.org/linux-staging/[e-mail]/T/#m1d3de7d2fa73b2447274858353bbd4a0c3a8ba14

Signed-off-by: Umang Jain <[e-mail]>
Reviewed-by: Stefan Wahren <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/vc04_services/interface/TODO

···
   to manage these buffers as dmabufs so that we can zero-copy import
   camera images into vc4 for rendering/display.
 
+* Fix kernel module support
+
+Even the VPU firmware doesn't support a VCHI re-connect, the driver
+should properly handle a module unload. This also includes that all
+resources must be freed (kthreads, debugfs entries, ...) and global
+variables avoided.
+
 * Documentation
 
 A short top-down description of this driver's architecture (function of

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c

···
 
 int vchiq_shutdown(struct vchiq_instance *instance)
 {
-	struct vchiq_state *state = instance->state;
-	struct vchiq_arm_state *arm_state;
 	int status = 0;
+	struct vchiq_state *state = instance->state;
 
 	if (mutex_lock_killable(&state->mutex))
 		return -EAGAIN;
···
 	mutex_unlock(&state->mutex);
 
 	dev_dbg(state->dev, "core: (%p): returning %d\n", instance, status);
-
-	arm_state = vchiq_platform_get_arm_state(state);
-	kthread_stop(arm_state->ka_thread);
 
 	free_bulk_waiter(instance);
 	kfree(instance);
···
 		goto shutdown;
 	}
 
-	while (!kthread_should_stop()) {
+	while (1) {
 		long rc = 0, uc = 0;
 
 		if (wait_for_completion_interruptible(&arm_state->ka_evt)) {

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c

···
 
 	DEBUG_INITIALISE(local);
 
-	while (!kthread_should_stop()) {
+	while (1) {
 		DEBUG_COUNT(SLOT_HANDLER_COUNT);
 		DEBUG_TRACE(SLOT_HANDLER_LINE);
 		remote_event_wait(&state->trigger_event, &local->trigger);
···
 	if (!found)
 		return -ENOMEM;
 
-	while (!kthread_should_stop()) {
+	while (1) {
 		remote_event_wait(&state->recycle_event, &local->recycle);
 
 		process_free_queue(state, found, length);
···
 			state->remote->slot_sync);
 	int svc_fourcc;
 
-	while (!kthread_should_stop()) {
+	while (1) {
 		struct vchiq_service *service;
 		int msgid, size;
 		int type;
···
 		(void)vchiq_remove_service(instance, service->handle);
 		vchiq_service_put(service);
 	}
-
-	kthread_stop(state->sync_thread);
-	kthread_stop(state->recycle_thread);
-	kthread_stop(state->slot_handler_thread);
 }
 
 int