Merge branch 'drm-intel-next' of git://anongit.freedesktop.org/drm-intel into drm-next

drm-intel-next-2016-08-22:
- bugfixes and cleanups for rcu-protected requests (Chris)
- atomic modeset fixes for gpu reset on pre-g4x (Maarten&Ville)
- guc submission improvements (Dave Gordon)
- panel power sequence cleanup (Imre)
- better use of stolen and unmappable ggtt (Chris), plus prep work to make that
  happen
- rework of framebuffer offsets, prep for multi-plane framebuffers (Ville)
- fully partial ggtt vmaps, including fenced ones (Chris)
- move lots more of the gem tracking from the object to the vma (Chris)
- tune the command parser (Chris)
- allow fbc without fences on recent platforms (Chris)
- fbc frontbuffer tracking fixes (Chris)
- fast prefaulting using io-mappping.h pgprot caching (Chris)

* 'drm-intel-next' of git://anongit.freedesktop.org/drm-intel: (141 commits)
  io-mapping: Fixup for different names of writecombine
  io-mapping.h: s/PAGE_KERNEL_IO/PAGE_KERNEL/
  drm/i915: Update DRIVER_DATE to 20160822
  drm/i915: Use remap_io_mapping() to prefault all PTE in a single pass
  drm/i915: Embed the io-mapping struct inside drm_i915_private
  io-mapping: Always create a struct to hold metadata about the io-mapping
  drm/i915/fbc: Allow on unfenced surfaces, for recent gen
  drm/i915/fbc: Don't set an illegal fence if unfenced
  drm/i915: Flush delayed fence releases after reset
  drm/i915: Reattach comment, complete type specification
  drm/i915/cmdparser: Accelerate copies from WC memory
  drm/i915/cmdparser: Use binary search for faster register lookup
  drm/i915/cmdparser: Check for SKIP descriptors first
  drm/i915/cmdparser: Compare against the previous command descriptor
  drm/i915/cmdparser: Improve hash function
  drm/i915/cmdparser: Only cache the dst vmap
  drm/i915/cmdparser: Use cached vmappings
  drm/i915/cmdparser: Add the TIMESTAMP register for the other engines
  drm/i915/cmdparser: Make initialisation failure non-fatal
  drm/i915: Stop discarding GTT cache-domain on unbind vma
  ...

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;
 };