drm/ttm: alter cpu_writers to return -EBUSY in ttm_execbuf_util reservations

This is similar to other platforms that don't allow command submission
to buffers locked on the cpu.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -1053,16 +1053,6 @@ int ttm_bo_mem_space(struct ttm_buffer_object *bo,
 }
 EXPORT_SYMBOL(ttm_bo_mem_space);
 
-int ttm_bo_wait_cpu(struct ttm_buffer_object *bo, bool no_wait)
-{
-	if ((atomic_read(&bo->cpu_writers) > 0) && no_wait)
-		return -EBUSY;
-
-	return wait_event_interruptible(bo->event_queue,
-					atomic_read(&bo->cpu_writers) == 0);
-}
-EXPORT_SYMBOL(ttm_bo_wait_cpu);
-
 int ttm_bo_move_buffer(struct ttm_buffer_object *bo,
 			struct ttm_placement *placement,
 			bool interruptible, bool no_wait_reserve,
@@ -1788,8 +1778,7 @@ EXPORT_SYMBOL(ttm_bo_synccpu_write_grab);
 
 void ttm_bo_synccpu_write_release(struct ttm_buffer_object *bo)
 {
-	if (atomic_dec_and_test(&bo->cpu_writers))
-		wake_up_all(&bo->event_queue);
+	atomic_dec(&bo->cpu_writers);
 }
 EXPORT_SYMBOL(ttm_bo_synccpu_write_release);
 

drivers/gpu/drm/ttm/ttm_execbuf_util.c

@@ -185,10 +185,7 @@ retry_this_bo:
 			ttm_eu_backoff_reservation_locked(list);
 			spin_unlock(&glob->lru_lock);
 			ttm_eu_list_ref_sub(list);
-			ret = ttm_bo_wait_cpu(bo, false);
-			if (ret)
-				return ret;
-			goto retry;
+			return -EBUSY;
 		}
 	}
 

include/drm/ttm/ttm_bo_api.h

@@ -424,8 +424,9 @@ extern void ttm_bo_unlock_delayed_workqueue(struct ttm_bo_device *bdev,
  * @no_wait: Return immediately if buffer is busy.
  *
  * Synchronizes a buffer object for CPU RW access. This means
- * blocking command submission that affects the buffer and
- * waiting for buffer idle. This lock is recursive.
+ * command submission that affects the buffer will return -EBUSY
+ * until ttm_bo_synccpu_write_release is called.
+ *
  * Returns
  * -EBUSY if the buffer is busy and no_wait is true.
  * -ERESTARTSYS if interrupted by a signal.

include/drm/ttm/ttm_bo_driver.h

@@ -726,20 +726,6 @@ extern void ttm_bo_mem_put(struct ttm_buffer_object *bo,
 extern void ttm_bo_mem_put_locked(struct ttm_buffer_object *bo,
 				  struct ttm_mem_reg *mem);
 
-/**
- * ttm_bo_wait_for_cpu
- *
- * @bo: Pointer to a struct ttm_buffer_object.
- * @no_wait: Don't sleep while waiting.
- *
- * Wait until a buffer object is no longer sync'ed for CPU access.
- * Returns:
- * -EBUSY: Buffer object was sync'ed for CPU access. (only if no_wait == 1).
- * -ERESTARTSYS: An interruptible sleep was interrupted by a signal.
- */
-
-extern int ttm_bo_wait_cpu(struct ttm_buffer_object *bo, bool no_wait);
-
 extern void ttm_bo_global_release(struct drm_global_reference *ref);
 extern int ttm_bo_global_init(struct drm_global_reference *ref);