drm: Make locked tasklet handling more robust.

Initialize the spinlock unconditionally when struct drm_device is filled in,
and return early in drm_locked_tasklet() if the driver doesn't support IRQs.
Signed-off-by: Dave Airlie <airlied@linux.ie>

drivers/char/drm/drm_irq.c

@@ -119,7 +119,6 @@ static int drm_irq_install(drm_device_t * dev)
 		init_waitqueue_head(&dev->vbl_queue);
 
 		spin_lock_init(&dev->vbl_lock);
-		spin_lock_init(&dev->tasklet_lock);
 
 		INIT_LIST_HEAD(&dev->vbl_sigs.head);
 		INIT_LIST_HEAD(&dev->vbl_sigs2.head);
@@ -456,7 +455,8 @@ void drm_locked_tasklet(drm_device_t *dev, void (*func)(drm_device_t*))
 	unsigned long irqflags;
 	static DECLARE_TASKLET(drm_tasklet, drm_locked_tasklet_func, 0);
 
-	if (test_bit(TASKLET_STATE_SCHED, &drm_tasklet.state))
+	if (!drm_core_check_feature(dev, DRIVER_HAVE_IRQ) ||
+	    test_bit(TASKLET_STATE_SCHED, &drm_tasklet.state))
 		return;
 
 	spin_lock_irqsave(&dev->tasklet_lock, irqflags);

drivers/char/drm/drm_stub.c

@@ -61,6 +61,7 @@ static int drm_fill_in_dev(drm_device_t * dev, struct pci_dev *pdev,
 
 	spin_lock_init(&dev->count_lock);
 	spin_lock_init(&dev->drw_lock);
+	spin_lock_init(&dev->tasklet_lock);
 	init_timer(&dev->timer);
 	mutex_init(&dev->struct_mutex);
 	mutex_init(&dev->ctxlist_mutex);