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Diffstat (limited to 'include/uapi/drm/i915_drm.h')
-rw-r--r--include/uapi/drm/i915_drm.h16
1 files changed, 15 insertions, 1 deletions
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 452629de7a57..5501fe83ed92 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -855,7 +855,16 @@ struct drm_i915_gem_busy {
* having flushed any pending activity), and a non-zero return that
* the object is still in-flight on the GPU. (The GPU has not yet
* signaled completion for all pending requests that reference the
- * object.)
+ * object.) An object is guaranteed to become idle eventually (so
+ * long as no new GPU commands are executed upon it). Due to the
+ * asynchronous nature of the hardware, an object reported
+ * as busy may become idle before the ioctl is completed.
+ *
+ * Furthermore, if the object is busy, which engine is busy is only
+ * provided as a guide. There are race conditions which prevent the
+ * report of which engines are busy from being always accurate.
+ * However, the converse is not true. If the object is idle, the
+ * result of the ioctl, that all engines are idle, is accurate.
*
* The returned dword is split into two fields to indicate both
* the engines on which the object is being read, and the
@@ -878,6 +887,11 @@ struct drm_i915_gem_busy {
* execution engines, e.g. multiple media engines, which are
* mapped to the same identifier in the EXECBUFFER2 ioctl and
* so are not separately reported for busyness.
+ *
+ * Caveat emptor:
+ * Only the boolean result of this query is reliable; that is whether
+ * the object is idle or busy. The report of which engines are busy
+ * should be only used as a heuristic.
*/
__u32 busy;
};